Induction of theta-positive lymphocytes and lymphoblasts in mouse bone marrow by mitogens.

With a sensitive technique for the identification of lymphocytes and lymphoblasts bearing the surface antigens phi, TL, and immunoglobulin, the induction of phi-positive small lymphocytes in bone marrow could be observed. Dibutyryl cyclic adenosine 3',5'-monophosphate and thymosin were both effective in inducing precursor cells to express phi antigen. Concanavalin A and bacterial lipopolysaccharide were also shown to be inducers. After treatment with concanavalin A but not with lipopolysaccharide, lymphoblasts developed in marrow cultures which were positive for phi and TL antigens; when spleen was cultured with concanavalin A, lymphoblasts were phi-positive and TL negative. It is concluded that the cell responsive to concanavalin A (and phytohemagglutinin) in bone marrow is a phi-negative precursor (stem) cell, which is induced first to express phi and TL antigens, and then to differentiate to a lymphoblast.