IgG subclass recognition of Loa loa antigens and their correlation with clinical status in individuals from Gabon

In endemic areas for Loa loa, a significant percentage of actively infected individuals have no circulating microfilariae, an observation which implies the existence of a stage-specific immune response. In an attempt to define the immunological basis of the amicrofilaraemic state, the reactivity of antigens from adult, microfilariae and infective larvae of L. loa was examined by Western blotting with individual serum samples from four clinically defined groups (high microfilaraemic, low microfilaraemic, amicrofilaraemic and endemic controls) using IgG subclass-specific reagents and IgE. In the adult parasite, a complex of antigens at 28-31 kDa was exclusively recognized by IgG1 from amicrofilaraemic individuals and, to a lesser extent, by IgG1 from endemic controls. However, this complex of antigens was recognized by IgG4 antibodies in serum samples from all individuals, including microfilaraemics. A microfilarial antigen of 21 kDa was recognized by IgG1 antibodies present in serum from amicrofilaraemic, endemic control and low microfilaraemic individuals. Persons with high levels of microfilariae did not recognise this antigen. In both the L3 and the microfilariae, a ladder antigen with increments of 15 kDa was the main target of IgG4 antibodies in amicrofilaraemic and microfilaraemic individuals. IgE antibodies recognized more antigens in the microfilarial stage than in the adult of L3. These results suggest that immunological differences between clinically defined groups are associated with the recognition of different antigens or epitopes.