CALPAIN IS THE TARGET ANTIGEN OF A TH1 CLONE THAT TRANSFERS PROTECTIVE IMMUNITY AGAINST SCHISTOSOMA-MANSONI

A CD4(+) clone (clone B), characterized as Th1 based on its selective production of IFN-gamma and IL-2, was established from C57Bl/6 mice pr otectively immunized against Schistosoma mansoni by intradermal vaccin ation with soluble worm Ags plus bacillus Calmette Guerin. In agreemen t with previous results demonstrating an IFN-gamma-dependent cell-medi ated protective mechanism in this vaccination model, Ag-elicited perit oneal macrophages from syngeneic recipients of this clone were activat ed to kill schistosome larvae (schistosomula) in vitro. Moreover, reci pients of clone B displayed significant resistance against cercarial c hallenge. By screening a battery of lambda gt11 clones from an adult w orm cDNA library, one recombinant (25B) was identified that stimulated clone B specifically. Analysis of the 25B cDNA insert revealed a nucl eotide sequence identical with that of the large subunit of schistosom e calpain, a Ca2+-activated neutral proteinase. By expressing the prod ucts of PCR subcloning, we identified a 146-amino acid region of the 2 5B gene containing immunologic activity equivalent to the whole polype ptide. Overlapping peptides spanning this region were synthesized, and a core epitope was identified with the sequence EWKGAWCDGS. Since clo ne B responds to supernatants from cultured schistosomula, we postulat e that the recognition of calpain released by invading larvae and resu lting induction of Th1 cytokines accounts for the protection mediated by the adoptively transferred clone. Our findings thus implicate calpa in as a target of protective immunity in schistosomes and provide the first example of a candidate vaccine Ag for this parasite identified o n the basis of T cell reactivity.