Evasion of Immunity IVertebrate and invertebrate immune systems.Dr. Jo Hamilton Parasitology BSIntroduction. lSuccessful parasites have evolved strategies for survival it is non-specific and has no memory component. Vertebrate immune system both innate and acquired components. Invertebrate immunity.The invertebrate immune system is comprised of two branches:lThe humoral response (N.B. this is not antibody mediated) is concerned with soluble components such as antimicrobial peptides (AMPs), agglutinins (lectins) and macrokines (these are similar to cytokines).lThe cellular response includes phagocytosis (haemocytes), encapsulation and nodulation.Invertebrate immunity humoral response.lAntimicrobial peptides. Wide range including defensins, cecropins, andropins, ceratotoxins, drosomycin & penaeidins etc. Their action leads to lysis of invading organism e.g. bacteria & protozoa.lMacrokines. There is growing evidence of these cytokine-like molecules. Haemolymph preparations have been shown to stimulate vertebrate immune effector cells (e.g. macrophages).lAgglutinins (lectins). Agglutinate invading organisms making them easier to phagocytose.Invertebrate immunity cellular response.lPhagocytosis - Haemocytes (amoebocytes) front line of invertebrate cellular. Foreign (non-self) invaders are taken into a phagocytotic vacuole where proteolytic enzymes & free oxygen radicals destroy the pathogen (in a similar way to vertebrate macrophages). Bacteria and yeast (10microns) can be phagocytosed.Invertebrate immunity cellular response contd.lEncapsulation - If invader too large for phagocytosis (e.g. the egg of a parasitic wasp), encapsulation might ensue. Invader is compacted under layer of haemocytes. This is accompanied by melanization. The melanized capsule adheres to host tissues but is walled off from the host. Phenoloxidases mediate melanization reaction but also have other tasks including wound healing, cuticle pigmentation & sclerotisation. Invertebrate immunity cellular response contd.lNodulation - Microaggregates of haemocytes & bacteria encased in haemocytes are melanised & removed from circulation.lPhagocytosis, encapsulation and nodulation mediated by eicosanoids (prostaglandins, leukotrienes).Invertebrate immunity mechanical / physical barriers.lIn addition to the cellular & humoral defences, invertebrates also have mechanical or physical defences.lThese include the cuticle, epithelia and in the case of insects the peritrophic membrane.Summary.By the end of this session you should be:lFamiliar with fundamental biology of vertebrate & invertebrate immune systems. lFamiliar with the concept of innate and acquired immunity in vertebrates.lRecoginise that invertebrates have only innate immune system.lRecognise the key players in both vertebrate and invertebrate immune systems.Next session.We will:lDescribe immunity to particular parasites.lExplore the strategies that parasites use to evade the hosts immune system.