CLONING, OVER-EXPRESSION AND EVALUATION OF A RECOMBINANT FUSION PROTEIN OF WUCHERERIA-BANCROFTI TOWARDS ITS APPLICATION AS A DIAGNOSTIC AGENT FOR BANCROFTIAN FILARIASIS

A low molecular weight (1 5 kDa) surface antigen of the cattle filarial nematode, Setaria digitata, was earlier shown to be specifically recognized by the antibodies from human bancroftian filarial (Mf positive) patients' sera (Theodore & Kaliraj, 1990). The filarial specific antibodies bound to a 15 kDa peptide in preparative Western blots were eluted and employed in screening of candidate antigens expressed in the genomic library of Wuchereria bancrofti at the IgG4 subclass antibody level. A recombinant clone (lambda WbG7) reacting strongly with filarial sera but poorly with sera from patients infected with non-filarial helminths was selected for further studies. The 2 kb DNA insert of the clone lambda WbG7 was recloned into a pMAL vector and the recombinant clone pGT7 thus obtained was over-expressed and affinity purified. The purified 105 kDa fusion protein of the clone pGT7 was specific and was not recognized by the non-filarial sera at the IgG4 level. All microfilaraemic individuals were positive by IgG4 assay. However, similar attempts to diagnose by filarial-specific IgE assays failed to recognize microfilaraemic individuals. Moreover, by filarial-specific IgG4 assays, the endemic normals were distinctly divided into two groups, showing higher and lower recognition for this antigen indicating current and past/no infection. Among the filarial-IgG4 (assay)-positive 'endemic normals', 14% showed 'microfilariae' during repeated peripheral night blood examination, confirming the validity of the recombinant antigen, pGT7 based assay.