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 inhibi tors indicated it to be a metallo-protease. IgG from chronic filarial patie nts living in an area of Orissa, India, endemic for Wuchereria bancrofti wa s able to neutralize the proteolytic activity of this enzyme completely. Ig G from asymptomatic microfilaraemics and endemic normals (asymptomatic amic rofilaraemics) only caused partial inhibition and IgG from non-endemic norm als was ineffective. The generation of inhibitory antibodies appears to dep end on the severity of filariasis. Evaluation of IgG-subclass response to the protease indicated the dominance of IgG(4) antibodies in asymptomatic carriers and of IgG(1) in those with chronic filariasis. The IgG(3) response was minimal and the IgG(2) response s were similar for each of the filarial groups. When IgG(4)-subclass serolo gy using the protease antigen was assessed, 47 of 50 microfilaraemics, 20 o f 50 endemic normals and 23 of 50 chronic patients but none of 20 non-endem ic normals were found seropositive. Appreciable levels of specific IgE, whi ch correlated with those of IgG(4), were detected in all filarial groups. I gG(4) was detected in 35 out of 70 children (aged < 12 years) who appeared amicrofilariaemic and 38 of 40 microfilaraemic children.