Mosquito - Plasmodium interactions in response to immune activation of thevector

During the development of Plasmodium sp, within the mosquito midgut, the pa rasite undergoes a series of developmental changes. The elongated ookinete migrates through the layers of the midgut where it forms the oocyst under t he basal lamina. We demonstrate here that if Aedes aegypti or Anopheles gam biae, normally susceptible to Plasmodium gallinaceum and P. berghei, respec tively, are immune activated by the injection of bacteria into the hemocoel , and subsequently are fed on an infectious bloodmeal, there is a significa nt reduction in the prevalence and mean intensity of infection of oocysts o n the midgut. Only those mosquitoes immune activated prior to, or immediate ly after, parasite ingestion exhibit this reduction in parasite development . Mosquitoes immune activated 2-5 days after bloodfeeding show no differenc es in parasite burdens compared with naive controls. Northern analyses reve al that transcriptional activity for mosquito defensins is not detected in the whole bodies of Ae. aegypti from 4 h to 10 days after ingesting I? gall inaceum, suggesting that parasite ingestion; passage from the food bolus th rough the midgut, oocyst formation, and subsequent release of sporozoites i nto the hemolymph do not induce the production of defensin. However, revers e transcriptase-PCR of RNA isolated solely from the midguts of Ae. aegypti indicates that transcription of mosquito defensins occurs in the midguts of naive mosquitoes and those ingesting an infectious or noninfectious bloodm eal. Bacteria-challenged Ae. aegypti showed high levels of mature defensin in the hemolymph that correlate with a lower prevalence and mean intensity of infection with oocysts. Because few oocysts were found on the midgut of immune-activated mosquitoes, the data suggest,that some factor, induced by bacterial challenge, kills the parasite at a preoocyst stage. (C) 1999 Acad emic Press.