Melanization of Sephadex beads by the malaria vector, Anopheles gambiae: effect of blood meal, and mechanisms of reproductive costs
, Ahmed, A. M. . 2005
Melanization is the main immune response killing malaria parasite in the gut of the malaria refractory mosquitoes. This study investigates this response against Sephadex beads model in the malaria susceptible Anopheles gambiae at 20 h post-beads inoculation. Follicular apoptosis and resorption have been investigated as two suggested mechanisms underlying reproductive costs as a result of this immune response. Thus, one of two different beads was inoculated into mosquito thoracic haemocoel, either a negatively charged CM C-25 or a neutral CM G-25 one. Melanization was relatively strong against neutral G-25 beads in sugar-fed mosquitoes, and become noticeably stronger after a blood meal. In contrast, melanization was relatively weak against negatively charged C-25 beads in both sugar- and blood-fed mosquitoes. This study also shows follicular apoptosis and follicular resorption as two main factors contributing to beads melanization-induced inhibition in mosquito oogenesis. The mean % of follicular resorption was significantly higher in the ovaries of C-25 beads inoculated mosquitoes compared to that in the ovaries of both control and those injected with Aedes physiological saline (APS). However, it was significantly lower than that in the ovaries of G-25 beads inoculated mosquitoes-which showed an overall significant more follicular resorption compared to all experimental mosquitoes. Thus, beads melanization and the concomitant follicular resorption seem to be depended on the type of inoculated bead. Such differences may, on one hand, mirror the variation of mosquito immune efficacy against different malaria parasites in natural populations and, on the other hand, limit the malaria immuno-control strategies.
