Publication details
Hemocyte-mediated immune response to biological and chemical agents in insects
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| Year of publication | 2008 |
| Type | Conference abstract |
| MU Faculty or unit | |
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| Description | The insects respond to invading microorganisms with strong innate immune system including hemocyte-mediated cellular and humoral immune responses that share many similarities with vertebrate immune systems. Cellular (or hemocytic) immune responses include nodulation (viral, bacterial and fungal spore infections), encapsulation (organisms larger than hemocytes and parasitoid eggs) and phagocytosis and coagulations. Nodulation is the first step of the cellular defense reactions to microbial infections in insects. Foreign abiotic or biotic antigens, when too large to be phagocytosed, are nodulated or encapsulated. Unlike phagocytosis, nodulation and encapsulation result in the formation of an overlapping sheath of hemocytes around a target. Nodules and capsules melanize in some insect species but not others. Coagulation of hemolymph after wounding is typical cooperation between cellular and humoral parts of insect immune system. Humoral immune responses involve the induced biosynthesis of various antibacterial and antifungal proteins, and induction of the prophenoloxidase (PPO) cascade. Phenoloxidase (PO) is a vital enzyme involved in a number of crucial processes, such as defense, wound healing, sclerotization, and pigmentation. Since active PO generates deleterious quinonoid compounds, most insects preserve this enzyme in the inactive proform and activate it upon necessity. Eicosanoids are crucial mediators of phagocytosis, microaggregation, cell spreading and nodulation reactions. Eicosanoids are produced by enzymatic oxygenation of arachidonic acid (AA) and two other C20 polyunsaturated fatty acids. PLA2 occurs in the fat body and hemocytes, and is elevated in response to bacterial challenge releasing AA, a precursor of eicosanoids. It has been shown that cellular PLA(2)s in hemocytes from tobacco hornworms, Manduca sexta are targets of immune-suppressive factors from the entomopathogenic bacteria Serratia marcescens and Xenorhabdus nematophila. Recently, we also demonstrated that eicosanoids mediate nodulation reactions to viral infection . |