Induction of theta-positive murine lymphocytes by a thymic extract.

Extracts of calf thymus were prepared using a modification of A. Goldstein's procedure for thymosin isolation. Several extracts were clearly active in inducing the formation of theta-antigen on the surface of immature murine lymphocytes. Surface theta-antigen was directly measured by using a live cell immunofluorescent technique. Some extracts were marginally active in affecting mitogen responsiveness, as measured by tritiated thymidine uptake. Sources of lymphocytes included adult bone marrow, spleen, thymus, lymph node and fetal liver cells.