The innate immune system comprises the cells and mechanisms that defend the host from infection by other organisms, in a non-specific manner. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Immune system|Passive immunity|Innate immune system The adaptive immune system is composed of highly specialized systemic cells and processes that eliminate or prevent Pathogenic This means that the cells of the innate system recognize, and respond to, pathogens in a generic way, but unlike the adaptive immune system, it does not confer long-lasting or protective immunity to the host. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Immune system|Passive immunity|Innate immune system The adaptive immune system is composed of highly specialized systemic cells and processes that eliminate or prevent Pathogenic  Innate immune systems provide immediate defense against infection, and are found in all classes of plant and animal life. Plants are living Organisms belonging to the kingdom Plantae.
The innate system is thought to constitute an evolutionarily older defense strategy, and is the dominant immune system found in plants, fungi, insects, and in primitive multicellular organisms (see Other forms of innate immunity). Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Multicellular organisms are Organisms consisting of more than one cell, and having Differentiated cells that perform specialized functions 
The major functions of the vertebrate innate immune system include:
Inflammation is one of the first responses of the immune system to infection or irritation. Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens Inflammation is stimulated by chemical factors released by injured cells and serves to establish a physical barrier against the spread of infection, and to promote healing of any damaged tissue following the clearance of pathogens. 
Chemical factors produced during inflammation (histamine, bradykinin, serotonin, leukotrienes also prostaglandilins) sensitize pain receptors, cause vasodilation of the blood vessels at the scene, and attract phagocytes, especially neutrophils. Histamine is a Biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a Neurotransmitter Bradykinin is a Peptide that causes blood vessels to enlarge (dilate and therefore causes blood pressure to lower Serotonin (ˌsɛrəˈtoʊnən ( 5-hydroxytryptamine, or 5-HT) is a Monoamine Neurotransmitter synthesized in serotonergic Neurons Leukotrienes are naturally produced Eicosanoid lipid mediators, which may be responsible for the effects of an inflammatory response A nociceptor is a Sensory receptor that sends signals that cause the perception of Pain in response to a potentially damaging stimulus The blood vessels are part of the Circulatory system and function to transport Blood throughout the body  Neutrophils then trigger other parts of the immune system by releasing factors that summon other leukocytes and lymphocytes.
The inflammatory response is characterized by the following symptom quintet: Redness (rubor) Heat (calor) Swelling (tumor) Pain (dolor) and possible dysfunction of the organs or tissues involved (functio laesa).
The complement system is a biochemical cascade of the immune system that helps, or “complements”, the ability of antibodies to clear pathogens or mark them for destruction by other cells. The complement system is a Biochemical cascade that helps clear Pathogens from an organism The complement system is a Biochemical cascade that helps clear Pathogens from an organism A biochemical cascade is a series of Chemical reactions in which the products of one reaction are consumed in the next reaction The cascade is composed of many plasma proteins, synthesized in the liver, primarily by hepatocytes. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Hepatocytes make up 70-80% of the Cytoplasmic mass of the Liver. The proteins work together to:
Elements of the complement cascade can be found in many species evolutionarily older than mammals including plants, birds, fish and some species of invertebrates. Plants are living Organisms belonging to the kingdom Plantae. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate 
All white blood cells (WBC) are known as leukocytes. Leukocytes are different from other cells of the body in that they are not tightly associated with a particular organ or tissue; thus, they function similar to independent, single-celled organisms. Leukocytes are able to move freely and interact and capture cellular debris, foreign particles, or invading microorganisms. Unlike many other cells in the body, most innate immune leukocytes cannot divide or reproduce on their own, but are the products of pluripotent hematopoietic stem cells present in the bone marrow. Hematopoietic stem cells (HSCs are Stem cells that give rise to all the blood cell types including Myeloid ( Monocytes and Macrophages, Neutrophils 
The innate leukocytes include: Natural killer cells, mast cells, eosinophils, basophils; and the phagocytic cells including macrophages, neutrophils and dendritic cells, and function within the immune system by identifying and eliminating pathogens that might cause infection. 
Mast cells are a type of innate immune cell that resides in the connective tissue and in the mucous membranes, and are intimately associated with defense against pathogens, wound healing, but are also often associated with allergy and anaphylaxis. A mast cell (or mastocyte) is a resident cell of several types of tissues and contains many granules rich in Histamine and Heparin Allergy is a disorder of the Immune system often also referred to as Atopy. Anaphylaxis is an acute systemic (multi-system and severe Type I Hypersensitivity allergic reaction in humans and other Mammals  When activated, mast cells rapidly release characteristic granules, rich in histamine and heparin, along with various hormonal mediators, and chemokines, or chemotactic cytokines into the environment. Histamine is a Biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a Neurotransmitter Heparin, a highly-sulfated Glycosaminoglycan, is widely used as an injectable Anticoagulant and has the highest negative Charge density of any known Chemokines are a family of small Cytokines, or Proteins secreted by cells Proteins are classified as chemokines according to shared structural characteristics Cytokines are a category of signalling Proteins and Glycoproteins that like Hormones and Neurotransmitters, are used extensively in cellular Histamine dilates blood vessels, causing the characteristic signs of inflammation, and recruits neutrophils and macrophages. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body 
The word 'phagocyte' literally means 'eating cell'. Phagocytosis is the cellular process of engulfing solid particles by the Cell membrane to form an internal Phagosome, or "food vacuole These are immune cells that engulf, i. e. phagocytose, pathogens or particles. To engulf a particle or pathogen, a phagocyte extends portions of its plasma membrane, wrapping the membrane around the particle until it is enveloped (i. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer e. the particle is now inside the cell). Once inside the cell, the invading pathogen is contained inside an endosome which merges with a lysosome. In Biology, an endosome is a membrane-bound compartment inside cells roughly 300-400 nm in diameter when fully mature Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases.  The lysosome contains enzymes and acids that kill and digest the particle or organism. Phagocytes generally patrol the body searching for pathogens, but are also able to react to a group of highly specialized molecular signals produced by other cells, called cytokines. Cytokines are a category of signalling Proteins and Glycoproteins that like Hormones and Neurotransmitters, are used extensively in cellular The phagocytic cells of the immune system include macrophages, neutrophils, and dendritic cells.
Phagocytosis of the hosts’ own cells is common as part of regular tissue development and maintenance. When host cells die, either internally induced by processes involving programmed cell death (also called apoptosis), or caused by cell injury due to a bacterial or viral infection, phagocytic cells are responsible for their removal from the affected site. Programmed cell-death ( PCD) is death of a cell in any form mediated by an intracellular program  By helping to remove dead cells preceding growth and development of new healthy cells, phagocytosis is an important part of the healing process following tissue injury. Phagocytosis is the cellular process of engulfing solid particles by the Cell membrane to form an internal Phagosome, or "food vacuole
Macrophages, from the Greek, meaning "large eating cell", are large phagocytic leukocytes, which are able to move outside of the vascular system by moving across the cell membrane of capillary vessels and entering the areas between cells in pursuit of invading pathogens. Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Capillaries are the smallest of a body's Blood vessels measuring 5-10 μm in diameter which connect Arterioles and Venules and enable the interchange In tissues, organ-specific macrophages are differentiated from phagocytic cells present in the blood called monocytes. Monocyte is a type of Leukocyte, part of the Human body 's Immune system. Macrophages are the most efficient phagocytes, and can phagocytose substantial numbers of bacteria or other cells or microbes.  The binding of bacterial molecules to receptors on the surface of a macrophage triggers it to engulf and destroy the bacteria through the generation of a “respiratory burst”, causing the release of reactive oxygen species. Respiratory burst (is sometimes called oxidative burst) is the rapid release of Reactive oxygen species (superoxide radical and hydrogen peroxide from different types Reactive oxygen species (ROS are ions or very small molecules that include Oxygen Ions free radicals, and Peroxides both inorganic and Pathogens also stimulate the macrophage to produce chemokines, which summons other cells to the site of infection. 
Neutrophils, along with two other cell types; eosinophils and basophils (see below), are known as granulocytes due to the presence of granules in their cytoplasm, or as polymorphonuclear cells (PMNs) due to their distinctive lobed nuclei. Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of White blood cells in humans and form an essential part of the Granulocytes are a category of White blood cells characterised by In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed Neutrophil granules contain a variety of toxic substances that kill or inhibit growth of bacteria and fungi. Similar to macrophages, neutrophils attack pathogens by activating a "respiratory burst". The main products of the neutrophil respiratory burst are strong oxidizing agents including hydrogen peroxide, free oxygen radicals and hypochlorite. An oxidizing agent or oxidising agent (also called an oxidant, oxidizer or oxidiser) can be defined as either a Chemical compound Hydrogen peroxide (H2O2 is a very pale blue liquid which appears colorless in a dilute solution slightly more Viscous than water The hypochlorite Ion is Cl[[Oxygen O]]− A hypochlorite compound is a Chemical compound containing this group with chlorine in Oxidation Neutrophils are the most abundant type of phagocyte, normally representing 50 to 60% of the total circulating leukocytes, and are usually the first cells to arrive at the site of an infection.  The bone marrow of a normal healthy adult produces more than 100 billion neutrophils per day, and more than 10 times that many per day during acute inflammation. In Medicine, an acute disease is a disease with either or both of a rapid onset a short course (as opposed to a chronic course 
Dendritic cells (DC) are phagocytic cells present in tissues that are in contact with the external environment, mainly the skin (where they are often called Langerhans cells), and the inner mucosal lining of the nose, lungs, stomach and intestines. Dendritic cells (DCs are Immune cells and form part of the Mammalian Immune system. The skin is the outer covering of living tissue of an animal (or plant Not to be confused with the Beta cells making up the Islets of Langerhans. Anatomically a nose is a protuberance in Vertebrates that houses the Nostrils or nares which admit and expel air for respiration in conjunction with the lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists  They are named for their resemblance to neuronal dendrites, but dendritic cells are not connected to the nervous system. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information Dendrites (from Greek δένδρον déndron, “tree” are the branched projections of a Neuron that act to conduct the electrochemical The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself Dendritic cells are very important in the process of antigen presentation, and serve as a link between the innate and adaptive immune systems. Antigen presentation is a process in the body's Immune system by which Macrophages, Dendritic cells and other cell types capture Antigens and Immune system|Passive immunity|Innate immune system The adaptive immune system is composed of highly specialized systemic cells and processes that eliminate or prevent Pathogenic
Basophils and eosinophils are cells related to the neutrophil (see above). Eosinophil granulocytes, usually called eosinophils (or less commonly acidophils) are White blood cells that are one of the Immune System components Eosinophil granulocytes, usually called eosinophils (or less commonly acidophils) are White blood cells that are one of the Immune System components When activated by a pathogen encounter, basophils releasing histamine are important in defense against parasites, and play a role in allergic reactions (such as asthma). Histamine is a Biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a Neurotransmitter Parasitism is a type of symbiotic relationship between Organisms of different Species. Allergy is a disorder of the Immune system often also referred to as Atopy. Asthma is a chronic Condition involving the Respiratory system in which the airways occasionally constrict become inflamed, and are  Upon activation, eosinophils secrete a range of highly toxic proteins and free radicals that are highly effective in killing bacteria and parasites, but are also responsible for tissue damage occurring during allergic reactions. Toxicity is the degree to which a substance is able to damage an exposed organism Activation and toxin release by eosinophils is therefore tightly regulated to prevent any inappropriate tissue destruction. 
Natural killer cells, or NK cells, are a component of the innate immune system. Natural killer cells (or NK cells) are a type of Cytotoxic Lymphocyte that constitute a major component of the Innate immune system. Natural killer cells (or NK cells) are a type of Cytotoxic Lymphocyte that constitute a major component of the Innate immune system. NK cells attack host cells that have been infected by microbes, but do not directly attack invading microbes. For example, NK cells attack and destroy tumor cells, and virus-infected cells, through a process known as "missing-self. See also Cancer A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic " This term describes cells with low levels of a cell-surface marker called MHC I (major histocompatibility complex) - a situation that can arise in viral infections of host cells. The major histocompatibility complex ( MHC) is a large genomic region or Gene family found in most Vertebrates It is the most gene-dense region  They were named "natural killer" because of the initial notion that they do not require activation in order to kill cells that are "missing self. "
Like other 'unconventional' T cell subsets bearing invariant T cell receptors (TCRs), such as CD1d-restricted Natural Killer T cells, γδ T cells exhibit characteristics that place them at the border between innate and adaptive immunity. The T cell receptor or TCR is a molecule found on the surface of T lymphocytes (or T cells that is in general responsible for recognizing Antigens bound CD1d is a member of the CD1 (cluster of differentiation 1 family of Glycoproteins expressed on the surface of various human Antigen-presenting cells Natural killer T (NKT cells are a heterogeneous group of T cells that share properties of both T cells and natural killer (NK cells. On one hand, γδ T cells may be considered a component of adaptive immunity in that they rearrange TCR genes to produce junctional diversity and develop a memory phenotype. Immune system|Passive immunity|Innate immune system The adaptive immune system is composed of highly specialized systemic cells and processes that eliminate or prevent Pathogenic V(DJ recombination is a mechanism of Genetic recombination that occurs in Vertebrates which randomly selects and assembles segments of Genes encoding However, the various subsets may also be considered part of the innate immune system where a restricted TCR or NK receptors may be used as a pattern recognition receptor. Pattern recognition receptors, or PRR s are Proteins expressed by cells of the Immune system to identify molecules associated with microbial Pathogens For example, according to this paradigm, large numbers of Vγ9/Vδ2 T cells respond within hours to common molecules produced by microbes, and highly restricted intraepithelial Vδ1 T cells will respond to stressed epithelial cells. Non-peptidic antigens are low molecular weight compounds that stimulate human Vγ9/Vδ2 T cells.
The parts of the innate immune system have different specificity for different pathogens.
|Pathogen||Main examples ||Phagocytosis ||complement||NK cells|
|Intracellular and cytoplasmic virus||yes||no||yes|
|Intracellular bacteria||yes (specifically neutrophils, no for rickettsia)||no||yes (no for rickettsia)|
Cells of the innate immune system effectively prevent free growth of bacteria within the body; however, many pathogens have evolved mechanisms allowing them to evade the innate immune system. Phagocytosis is the cellular process of engulfing solid particles by the Cell membrane to form an internal Phagosome, or "food vacuole The complement system is a Biochemical cascade that helps clear Pathogens from an organism Natural killer cells (or NK cells) are a type of Cytotoxic Lymphocyte that constitute a major component of the Innate immune system. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable Mumps or epidemic Parotitis is a Viral disease of the Human species Measles (rubeola is a Disease caused by a virus specifically a Paramyxovirus of the genus Morbillivirus. Rhinovirus (from the Greek rhin - which means "nose" is a genus of the Picornaviridae family of Viruses Rhinoviruses The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Listeria monocytogenes is a Gram-positive Bacterium, in the division Firmicutes, named for Joseph Lister. Legionella is a Gram negative Bacterium, including species that cause Legionellosis or Legionnaires' disease most notably L Mycobacterium is a Genus of Actinobacteria, given its own family the Mycobacteriaceae Rickettsia is a Genus of motile, Gram-negative, non-sporeforming, highly Pleomorphic bacteria that can present Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of White blood cells in humans and form an essential part of the The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Staphylococcus (in Greek σταφυλη staphyle means bunch of grapes and κοκκος coccos means granule is a genus of Gram-positive Streptococcus is a Genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the Neisseria is a genus of Gram (- bacteria included among the Proteobacteria, a large group of Gram-negative forms Salmonella enterica is a rod shaped Flagellated Gram-negative Bacterium, and a member of the Genus Salmonella Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular Plasmodium malariae is a parasitic Protozoa that causes Malaria in humans and animals Leishmania is a Genus of Trypanosome Protozoa, and is the Parasite responsible for the disease Leishmaniasis. Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular For the infection and disease caused by this parasite refer to Amoebiasis. Giardia lamblia (synonymous with Lamblia intestinalis and Giardia duodenalis) is a Flagellated Protozoan A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Candida is a Genus of Yeasts Many species of this genus are Endosymbionts Histoplasma is a Genus of dimorphic Fungi commonly found in bird and bat Cryptococcus (literally "Hidden Seed" is a Genus of Fungus. 
Evasion strategies that circumvent the innate immune system include intracellular replication, such as in Salmonella, or a protective capsule that prevents lysis by complement and by phagocytes, as in Mycobacterium tuberculosis. Salmonella is a Genus of rod-shaped Gram-negative enterobacteria that causes Typhoid fever, Paratyphoid fever Mycobacterium tuberculosis is the Bacterium that causes most cases of Tuberculosis.  Bacteroides species are normally commensal bacteria, making up a substantial portion of the mammalian gastrointestinal flora. Bacteroides is a Genus of Gram-negative, bacillis bacteria. Bacteroides species are non- Endospore -forming anaerobes In Ecology, commensalism is a kind of symbiotic relationship between two organisms where one benefits and the other is not significantly harmed or helped (like a bird The gut flora are the Microorganisms that normally live in the Digestive tract and can perform a number of useful functions for their hosts  Some species (B. fragilis, for example) are opportunistic pathogens, causing infections of the peritoneal cavity. An opportunistic infection is an infection caused by Pathogens that usually do not cause disease in a healthy Immune system. The peritoneal cavity is a potential space between the parietal Peritoneum and visceral peritoneum These species evade the immune system through inhibition of phagocytosis by affecting the receptors that phagocytes use to engulf bacteria or by mimicking host cells so that the immune system does not recognize them as foreign. Staphylococcus aureus inhibits the ability of the phagocyte to respond to chemokine signals. Staphylococcus aureus (ˌstæfɨləˈkɒkəs ˈɔriəs literally "Golden Cluster Seed" and also known as golden staph) is the most common cause of Other organisms such as M. tuberculosis, Streptococcus pyogenes and Bacillus anthracis utilize mechanisms that directly kill the phagocyte. Streptococcus pyogenes is a spherical Gram-positive Bacteria that grows in long chains and is the cause of Group A streptococcal infections Bacillus anthracis is a Gram-positive, facultatively anaerobic, rod-shaped Bacterium of the genus Bacillus.
Bacteria and fungi may also form complex biofilms, providing protection from the cells and proteins of the immune system; recent studies indicate that such biofilms are present in many successful infections, including the chronic Pseudomonas aeruginosa and Burkholderia cenocepacia infections characteristic of cystic fibrosis. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface Pseudomonas aeruginosa is a Gram-negative, aerobic, rod-shaped Bacterium with unipolar motility. Burkholderia cenocepacia is a Gram-negative bacteria that is common in the environment and may cause disease in plants Cystic fibrosis (also known as CF, mucoviscoidosis, or mucoviscidosis) is a hereditary disease affecting the exocrine (mucus glands of the lungs 
Bacteria (and perhaps other prokaryotic organisms), utilize a unique defense mechanism, called the restriction modification system to protect themselves from pathogens, such as bacteriophages. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other The restriction modification system ( RM system) is used by Bacteria, and perhaps other prokaryotic organisms to protect themselves from foreign DNA This article is about a biological infectious particle for other uses see Phage (disambiguation. In this system, bacteria produce enzymes, called restriction endonucleases, that attack and destroy specific regions of the viral DNA of invading bacteriophages. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins A restriction enzyme (or restriction Endonuclease) is an Enzyme that cuts double-stranded DNA at specific recognition Nucleotide Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Methylation of the host's own DNA marks it as "self" and prevents it from being attacked by endonucleases. Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates.  Restriction endonucleases and the restriction modification system exist exclusively in prokaryotes.
Invertebrates do not possess lymphocytes or an antibody-based humoral immune system, and it is likely that a multicomponent, adaptive immune system arose with the first vertebrates. An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate  Nevertheless, invertebrates possess mechanisms that appear to be precursors of these aspects of vertebrate immunity. Pattern recognition receptors are proteins used by nearly all organisms to identify molecules associated with microbial pathogens. Pattern recognition receptors, or PRR s are Proteins expressed by cells of the Immune system to identify molecules associated with microbial Pathogens Toll-like receptors are a major class of pattern recognition receptor, that exists in all coelomates (animals with a body-cavity), including humans. Toll-like receptors ( TLRs) are a class of single membrane-spanning non-catalytic receptors that recognize structurally conserved molecules derived from Microbes By the broadest definition a body cavity is any fluid filled space in a Multicellular organism.  The complement system, as discussed above, is a biochemical cascade of the immune system that helps clear pathogens from an organism, and exists in most forms of life. The complement system is a Biochemical cascade that helps clear Pathogens from an organism Some invertebrates, including various insects, crabs, and worms utilize a modified form of the complement response known as the prophenoloxidase (proPO) system. Crabs are decapod Crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (βραχύ / brachy A worm is a common name given to a diverse group of invertebrate animals that have a long soft body and no legs 
Antimicrobial peptides are an evolutionarily conserved component of the innate immune response found among all classes of life and represent the main form of invertebrate systemic immunity. Antimicrobial peptides (also called host defence peptides are an evolutionarily conserved component of the innate immune response and are found among all classes of life Immunity is a material term that describes a state of having sufficient biological defenses to avoid Infection, Disease, or other unwanted biological invasion Several species of insect produce antimicrobial peptides known as defensins and cecropins. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Defensins are small (15-20 residue) Cysteine -rich Cationic Proteins found in both Vertebrates and Invertebrates They are
Members of every class of pathogen which infect humans also infect plants. Although the exact pathogenic species vary with the infected species, bacteria, fungi, viruses, nematodes and insects can all cause plant disease. As with animals, plants attacked by insects or other pathogens use a set of complex metabolic responses that lead to the formation of defensive chemical compounds that fight infection or make the plant less attractive to insects and other herbivores. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell  (see: plant defense against herbivory). Plant defense against herbivory or host-plant resistance (HPR includes a range of Adaptations evolved
Like invertebrates, plants neither generate antibody or T-cell responses nor possess mobile cells that detect and attack pathogens. In addition, in case of infection, parts of some plants are treated as disposable and replaceable, in ways that very few animals are able to do. Walling off or discarding a part of a plant helps stop spread of an infection. 
Most plant immune responses involve systemic chemical signals sent throughout a plant. Plants use pattern-recognition receptors to identify pathogens and to start a basal response, which produces chemical signals that aid in warding off infection. When a part of a plant becomes infected with a microbial or viral pathogen, in case of an incompatible interaction triggered by specific elicitors, the plant produces a localized hypersensitive response (HR), in which cells at the site of infection undergo rapid programmed cell death to prevent the spread of the disease to other parts of the plant. The hypersensitive response (HR is a mechanism used by Plants, to prevent the spread of Infection by Microbial Pathogens The HR is characterized Programmed cell-death ( PCD) is death of a cell in any form mediated by an intracellular program HR has some similarities to animal pyroptosis, such as a requirement of caspase-1-like proteolytic activity of VPEγ, a cysteine protease that regulates cell disassembly during cell death. Pyroptosis is a form of Programmed cell death associated with antimicrobial responses during Inflammation. Caspases, or c ysteine- asp artic acid prote ases, are a family of Cysteine proteases which play essential roles in Apoptosis (programmed Proteases are Enzymes that degrade polypeptides. Cysteine proteases have a common catalytic mechanism that involves a nucleophilic Cysteine 
"Resistance" (R) proteins, encoded by R genes, are widely present in plants and detect pathogens. These proteins contain domains similar to the NOD Like Receptors and Toll-like receptors utilized in animal innate immunity. Pattern recognition receptors, or PRR s are Proteins expressed by cells of the Immune system to identify molecules associated with microbial Pathogens Toll-like receptors ( TLRs) are a class of single membrane-spanning non-catalytic receptors that recognize structurally conserved molecules derived from Microbes Systemic acquired resistance (SAR) is a type of defensive response that renders the entire plant resistant to a broad spectrum of infectious agents. In plants systemic acquired resistance (SAR is a "whole-plant" resistance response that occurs following an earlier localized exposure to a Pathogen. SAR involves the production of chemical messengers, such as salicylic acid or jasmonic acid. Salicylic acid (from the Latin word for the willow tree Salix, from whose bark it can be obtained is a Beta hydroxy acid (BHA with the formula Jasmonic acid (JA is a member of the Jasmonate class of Plant hormones It is biosynthesized from Linolenic acid by the Octadecanoid pathway Some of these travel through the plant and signal other cells to produce defensive compounds to protect uninfected parts, e. g. , leaves. Salicylic acid itself, although indispensable for expression of SAR, is not the translocated signal responsible for the systemic response. Recent evidence indicates a role for jasmonates in transmission of the signal to distal portions of the plant. RNA silencing mechanisms are also important in the plant systemic response, as they can block virus replication. RNA interference ( RNAi) is a mechanism that inhibits Gene expression at the stage of translation or by hindering the transcription of specific  The jasmonic acid response, is stimulated in leaves damaged by insects, and involves the production of methyl jasmonate. Jasmonic acid (JA is a member of the Jasmonate class of Plant hormones It is biosynthesized from Linolenic acid by the Octadecanoid pathway Methyl jasmonate (MeJA is a substance used in Plant defense and also under early research for cancer treatment in humans