The detection of F(ab')2-related surface antigens on the thymocytes of children.

A Fowl antiserum to human polyclonal F(ab')2 with specificities for variable region antigens of both light and heavy chains and for the constant portion of the Fd fragment bound to about 20 per cent of thymocytes from three children. Binding was completely inhibited by purified human polyclonal IgG and only partly by L chains. The fowl anti-F(ab')2 also bound to a subpopulation of peripheral blood lymphocytes which was somewhat larger than the B-cell population identified with other anti-immunoglobulin sera. Binding was detected by autoradiography and the amount of radiolabel seen on thymocytes was nearly as great as that on peripheral blood lymphocytes. As no binding to thymocytes was seen with other anti-immunoglobulin sera we propose that the fowl anti-F(ab')2 recognizes immunoglobulin or material with structural similarities which is synthesized by thymocytes but of which predominantly V region determinants are exposed on the membrane surface.