CLONING AND CHARACTERIZATION OF A POTENTIALLY PROTECTIVE CHITINASE-LIKE RECOMBINANT ANTIGEN FROM WUCHERERIA-BANCROFTI

While there is no direct evidence demonstrating the existence of prote ctive immunity to Wuchereria bancrofti infection in humans, the presen ce of individuals, in populations in areas where infection is endemic, with no clinical evidence of past or current infection despite apprec iable exposure to the infective larvae, suggests that protective immun ity to filarial parasites may occur naturally. Earlier work indicated that such putatively immune individuals generated antibodies to a 43-k Da antigen from larval extracts of the related filarial parasite Brugi a malayi that was recognized by only 8% of the infected population. Wi th rabbit antiserum raised against this 43-kDa antigen, this current s tudy identified a recombinant clone, WbN43, with an insert size of 2.3 kb, from a W. bancrofti genomic expression library. The recombinant f usion protein was differentially recognized by the putatively immune i ndividuals but not by the infected patients. The coding sequence (684 bp) from the 5' end had significant sequence similarity to chitinases from Serratia marcescens, Bacillus circulans, Streptomyces plicatus, a nd B. malayi. Peptide sequencing of the expressed product also defined a chitinase-like sequence. Molecular characterization indicated WbN43 to be a low-copy-number gene, with expression predominantly in infect ive larvae and microfilariae but not in adult parasites.