Differential recognition of a protective filarial antigen by antibodies from humans with bancroftian filariasis.

The objectives of this study were to identify filarial antigens which induce enhanced clearance of circulating microfilariae and to establish if human antibody reactivity with these molecules correlates with the apparent parasite burdens of residents of an endemic area of Bancroftian filariasis. Mice immunized with an extract of Brugia malayi microfilariae develop IgG antibodies to four major filarial antigens with an apparent molecular weight (Mr) of approximately 112,000, 60,000, 45,000, and 25,000. Animals immunized with gel slices containing the approximately 25,000-Mr antigen are resistant to intravenous challenge with live microfilariae (78-98% reduction in parasitemia vs. controls, P less than 0.01). A group of 22 amicrofilaremic humans had a significantly higher (P less than 0.025) mean antibody titer to the Mr 25,000-Mr antigen (1: 424) than 16 microfilaremic individuals (1:95). There were no significant differences between the two groups in antibody titers to filarial antigens of Mr approximately 112,000, 60,000, and 45,000 Mr. These data suggest that a high degree of reactivity to the 25,000-Mr antigen in humans with lymphatic filariasis correlates with a parasitologic status that is least conducive to transmission of infection.