Differential antibody response to parasite lipid antigens in lymphatic filariasis

Antibody response to lipid antigens from microfilariae of cattle filarial p arasite Setaria digitata was evaluated in human filarial sera of Orissa, In dia. Increased antibody (IgG and IgM) levels were observed in amicro-filara emic groups of chronic patients and endemic normals compared to microfilara emic carriers. Antibody levels were negligible in people living in nonfilar ial regions and in leprosy patients suggesting filariae specificity, Anti-l ipid antibodies were also found to be considerably elevated in Brugia malay i (L-3)-infected mastomys without microfilaraemia than in those animals wit h microfilariae, These data indicate that high antibody levels to lipid ant igens are associated with microfilariae negativity. Ige subclass analysis r evealed the predominance of IgG(2) in asymptomatic microfilaraemics IgG(3) and IgG(1) in chronic patients and IgG(1) end IgG(2) in endemic normals. Di ethylcarbamazine treatment in asymptomatic microfilaraemic subjects led to enhanced antibody response that sustained more than six months post treatme nt. The nature of antigenic determinant recognized by filarial antibodies w as assessed by periodate treatment and indicated these antigens to be glyco lipids, Periodate oxidation of lipids resulted in an overall decrease in an tibody binding, the magnitude of which varied depending on antibody isotype s and filarial groups. The periodate-sensitive carbohydrate epitopes were r ecognized by both IgG and IgM in asymptomatic microfilaraemic carrier sera, but only by IgG in endemic normals and chronic filarial sera; IgM binding in the latter sera remained unaffected. Carbohydrate recognition by filaria l antibodies seems to be dissimilar in different clinical groups of filaria sis and might modulate the course of filarial infection in humans.