Humoral response to the Anopheles gambiae salivary protein gSG6: IgG1 and IgG4 subclasses in exposed individuals from Burkina Faso.

The ability to monitor malaria transmission and to evaluate vector control measures are two basic ingredients of any effective anti-malaria intervention. The use of serology, in addition to classical parasitological and entomological methods, could represents an important complementary/alternative tool that may allow for wider, easier and perhaps more sensitive epidemiological analyses. In the course of mosquito salivary transcriptome studies we identified a group of anopheline-specific salivary proteins (i.e. not found so far in any other blood sucking arthropod) which could be useful as indicators of exposure to bites of malaria vectors. We have previously shown that the Anopheles gambiae salivary protein gSG6 is immunogenic and elicits an IgG response that (i) is short-lived, (ii) varies with the transmission season and (iii) is stronger in the ethnic group Fulani as compared to Mossi in West Africa (in preparation). Moreover, the anti-gSG6 IgG response decreases with age suggesting the involvement of some mechanism of tolerance as a consequence of the continued exposure to the antigen. To get further insights into the nature of this anti-gSG6 IgG response we measured the levels of IgG1 and IgG4 subclasses in human sera collected in a rural malaria hyperendemic area of Burkina Faso at the beginning and at the end of the transmission season, as well as during the following dry season. Overall the results are in line with our previous observations and high levels of anti-gSG6 IgG4 were found in exposed individuals. Data appear compatible with the involvement of a mechanism of desensitization and suggest that in high transmission/exposure areas this tolerance may take place early, most likely in 3 to 6 years old children.