Antigenicity of a filarial protease from Setaria digitata in Wuchereria bancrofti infection.

A protease isolated from adult Setaria digitata revealed a single, 110-kDa band in a gelatin-impregnated, substrate gel. Analysis with specific inhibitors indicated it to be a metallo-protease. IgG from chronic filarial patients living in an area of Orissa, India, endemic for Wuchereria bancrofti was able to neutralize the proteolytic activity of this enzyme completely. IgG from asymptomatic microfilaraemics and endemic normals (asymptomatic amicrofilaraemics) only caused partial inhibition and IgG from non-endemic normals was ineffective. The generation of inhibitory antibodies appears to depend on the severity of filariasis. Evaluation of IgG-subclass response to the protease indicated the dominance of IgG4 antibodies in asymptomatic carriers and of IgG1 in those with chronic filariasis. The IgG3 response was minimal and the IgG2 responses were similar for each of the filarial groups. When IgG4-subclass serology using the protease antigen was assessed, 47 of 50 microfilaraemics, 20 of 50 endemic normals and 23 of 50 chronic patients but none of 20 non-endemic normals were found seropositive. Appreciable levels of specific IgE, which correlated with those of IgG4, were detected in all filarial groups. IgG4 was detected in 35 out of 70 children (aged < 12 years) who appeared amicrofilariaemic and 38 of 40 microfilaraemic children.