MALARIA INFECTION OF THE MOSQUITO ANOPHELES-GAMBIAE ACTIVATES IMMUNE-RESPONSIVE GENES DURING CRITICAL TRANSITION STAGES OF THE PARASITE LIFE-CYCLE

Six gene markers have been used to map the progress of the innate immu ne response of the mosquito vector, Anopheles gambiae, upon infection by the malaria parasite, Plasmodium berghei, In addition to four previ ously reported genes, the set of markers included NOS (a nitric oxide synthase gene fragment) and ICHIT (a gene encoding two putative chitin -binding domains separated by a polythreonine-rich mucin region). In t he midgut, a robust response occurs at 24 h post-infection, at a time when malaria ookinetes traverse the midgut epithelium, but subsides at later phases of malaria development. In contrast, the salivary glands show no significant response at 24 h, but are activated in a prolonge d late phase when sporozoites are released from the midgut into the ha emolymph and invade the glands, between 10 and 25 days after blood fee ding. Furthermore, the abdomen of the mosquito minus the midgut shows significant activation of immune markers, with complex kinetics that a re distinct from those of both midgut and salivary glands; The parasit e evidently elicits immune responses in multiple tissues of the mosqui to, two of which are epithelia that the parasite must traverse to comp lete its development, The mechanisms of these responses and their sign ificance for malaria transmission are discussed.