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 micro-filariae, an observation which impli es the existence of a stage-specific immune response. In an attempt to defi ne the immunological basis of the amicrofilaraemic state, the reactivity of antigens from adult, microfilariae and infective larvae of L. loa was exam ined by Western blotting with individual serum samples from four clinically defined groups thigh microfilaraemic, low microfilaraemic, amicrofilaraemi c and endemic controls) using IgG subclass-specific reagents and IgE. In th e adult parasite, a complex of antigens at 28-31 kDa was exclusively recogn ized by IgG1 from amicrofilaraemic individuals and, to a lesser extent, by IgG1 from endemic controls. However, this complex of antigens was recognize d by IgG4 antibodies in serum samples from all individuals, including micro filaraemics. A microfilarial antigen of 21 kDa was recognized by IgG1 antib odies present in serum from amicrofilaraemic, endemic control and low micro filaraemic individuals. Persons with high levels of microfilariae did not r ecognise this antigen. In both the L3 and the microfilariae, a ladder antig en with increments of 15 kDa was the main target of IgG4 antibodies in amic rofilaraemic and microfilaraemic individuals. IgE antibodies recognized mor e antigens in the microfilarial stage than in the adult of L3. These result s suggest that immunological differences between clinically defined groups are associated with the recognition of different antigens or epitopes.