Division of Parasitology, National Institute for Medical Research, Mill Hill, London, U.K.
A cDNA clone from an adult Schistosoma mansoni lambda gt11 expression library (A12) encoding an antigenic polypeptide of 22 kDa is described. A12 is 797 bp long and has one open reading frame encoding a protein of 190 amino acids which does not contain a signal sequence or membrane anchor motif and has no homologies with any sequences on the currently available data bases. Its product (sm22.6) is recognised by antibodies from mice protectively vaccinated with purified adult S. mansoni tegumental membranes and by serum from S. mansoni-infected Brazilians. It is present in all post-snail life cycle stages except the egg, is not sex-specific, and is found in 9 species of Schistosoma, but not in a range of other helminths. Data are presented which suggest that sm22.6 is a soluble, peripheral membrane protein.