IDENTIFICATION OF A MAJOR T-CELL IMMUNOGEN IN THE ANTI-SCHISTOSOME RESPONSE OF ADULT RESIDENTS IN AN AREA ENDEMIC FOR SCHISTOSOMA-MANSONI

Vaccine-induced immunity to Schistosoma mansoni infection depends on t he specific priming of certain T cell subsets and on the recall of thi s response by natural infections months or years after vaccine adminis tration. Thus, those schistosome proteins that activate T cells in ind ividuals stimulated by natural infections are potential candidate vacc ine antigens. In the present study, we identified and purified one suc h T cell-stimulating antigen and evaluated its immunological propertie s in subjects living in an area endemic for Schistosoma mansoni. Chrom atography fractions (gel filtration, followed by ion exchange chromato graphy) of soluble extracts of schistosomula were screened for their a bility to stimulate schistosome-specific T cell clones derived from a subject sensitized by natural infection. A fraction stimulating most c lones was identified and characterized. A few nanograms of this fracti on, containing a major 9-10-kDa component, stimulated the T helper cel ls of most adults living in an endemic area of Brazil, and was able to trigger a strong cutaneous immediate hypersensitivity reaction. In co ntrast, children reacted weakly to this antigen preparation both in bl astogenesis and in skin tests, although they mounted a significant rea ction to crude larval antigen preparations. In conclusion, this work i dentifies a schistosomula antigen that induces a strong T cell respons e in adults sensitized by natural infections. This T cell response dev elops gradually in children and adolescents, is apparently not restric ted by the HLA haplotypes common in the study area, and allows the pro duction of parasite-specific IgE antibodies. Thus, this T cell respons e has some features of the immune response that is believed to protect chronically exposed humans from reinfection.