The humoral anti-bacterial response of Anopheles gambiae and the immunity-reproduction trade-off conflict: between the hope and limitation of the malaria immuno-control strategy
, Ahmed, A. M. . 2005
In this study, induction of the humoral anti-bacterial activity of the African human malaria vector, Anopheles gambiae, and the mechanisms of the concomitant fecundity reduction were investigated. The blood meal induced a humoral anti-Micrococcus luteus activity, which was detectable at 12h, peaked around 24h and become hardly detectable at 48h post-feeding. This humoral activity was also detected in sugar-fed mosquitoes at 18h post-intrathoracic injection with the immune elicitor, lipopolysaccharide (LPS, 10ng/mosquito). Moreover, the blood meal significantly enhanced the immune-stimulatory effect of LPS when injected into blood-fed mosquitoes, as a significant higher anti-M. luteus activity was detected compared to that of LPS-injected sugar-fed mosquitoes. These data suggest an immune enhancive effect of blood meal, which could be in the favour of malaria immuno-control strategy. On the other hand, induction of this immune activity did impose a reproductive cost, as LPS-injected mosquitoes showed a significant 28.8% fecundity reduction compared to those injected with Aedes physiological saline (APS). Follicular apoptosis and resorption were investigated in this study as two suggested mechanisms of this fecundity reduction. On one hand, follicular apoptosis was clearly detectable as early as 18h post-LPS injection, which seems to occur within epithelial cells not in nurse cells. On the other hand, follicular resorption was detected 18h post-LPS injection, which was 44.5% significantly higher than that in APS-injected mosquitoes. Based on these data, this study suggests that involving the humoral immune response in the battle against malaria would be costly in terms of fecundity reduction. Thus, as part of the scenario of immunity-reproduction conflict, the discussion of these data concludes by suggesting that the impact of immune stimulation on the vector fecundity would participate as a limiting factor to the success of malaria immuno-control strategy.
