Evaluation of IgG4 response against Chrysops spp. molecules in long-term stocked plasma from humans exposed to Loa loa.

Chrysops silacea and Chrysops dimidiata are the main vectors of the human filarial disease caused by Loa loa but also a potential carrier of other parasites, bacteria, or viruses. The female feeds on blood from humans and from non-human species. Studies about African Chrysops species are scarce. In this context, we evaluated the detection of IgG4 against Chrysops molecules in samples from humans exposed to Loa loa infection stored for 20 yr. Fresh extracts of proteins from uninfected and unfed C. silacea were analyzed through enzyme-linked immunosorbent assay (ELISA) and western blotting for the detection of human IgG4 and IgE. The results of this analysis were compared between non-exposed populations and populations exposed to three different daily biting rates (DBR) of 3, 13, and 106 bites. The level of human IgG4 was significantly elevated in populations exposed to Chrysops bites compared with the non-exposed population (0.751 ± 0.826 vs. 0.209 ± 0.217; P = 0.0052). There was a general trend showing a correlation between the intensity of exposure and the level of IgG4 (r = 0.192, P = 0.044). Identification of Chrysops molecules reactive against IgG4 showed a prominent 13- and 14-kDa band among villagers exposed to a DBR of 13 or 106, while the reactivity was very weak in villagers with a DBR of 3 and was absent in the non-exposed group. The long-lasting response of IgG4 in old stocked samples may be informative.