MAPPING OF THE ANTIGENIC DETERMINANTS OF THE LEISHMANIA-INFANTUM GP63PROTEIN RECOGNIZED BY ANTIBODIES ELICITED DURING CANINE VISCERAL LEISHMANIASIS

The gp63 gene encoding the major surface antigen of Leishmania infantu m has been cloned and sequenced. In spite of the overall sequence homo logy with the gp63 genes from other Leishmania species, particularly w ith the constitutively expressed Leishmania chagasi Gp63 gene, the car boxy-terminal ends of these genes are clearly divergent (62% homology) . To study the prevalence of anti-gp63 antibodies in the sera from dog s with visceral leishmaniasis, a recombinant L. infantum gp63 protein was expressed in Escherichia coli. It was found that 100% of the sera from these dogs recognized the recombinant gp63 protein, suggesting th at it must function as a potent B cell immunogen during natural canine visceral leishmaniasis. However, heterogeneity in the level of respon se was observed. Fine mapping of the antigenic determinants was perfor med by means of 6 overlapping subfragments of the gp63 protein and by the use of a library of synthetic peptides. The data showed that there is some degree of immunological restriction in the recognition of the protein since reactivity was observed preferentially against the most divergent region. The epitope mapping of this region showed 2 immunod ominant peptides the response to which seems to be preferentially of t he IgG2 type.