Unmasking and Functional Characterization of T ‐Cell‐Replacing Factors Obtained from Super‐natants of Allogeneic Spleen Cell Mixtures

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Abstract
Supernatants from allogeneic spleen cell mixtures contain factors that replace both thymus‐derived lymphocytes and adherent macrophage‐equivalent cells in the in vitro primary antibody response to sheep erythrocytes The making of these cell‐replacing products requires the initial presence of allogeneic thymus‐derived lymphocytes, but the final producer appears to be the adherent cell Inhibition of DNA synthesis of allogeneic spleen cell mixtures prevents formation of these cell‐replacing factors It is the late maturation processes leading to the formation of high‐rate antibody‐producing cells among the antigen‐specific bone marrow‐derived splenic lymphocytes that are amplified by soluble products from supernatants of allogeneic spleen cells, because such supernatants are most active when added to purified splenic bone marrow cells that have been in contact with antigen for 48 hr. Both these early and late maturation processes of splenic bone marrow cells are sensitive to mitomycin C and require the continuous presence of antigen. A model is presented where activated thymus‐derived lymphocytes alarm macrophages to secrete a product that helps bone marrow‐derived lymphocytes that have been in primary contact with antigen to develop and mature into high‐rate antibody‐forming cells.