Increased proliferation of activated T-lymphocytes in response to a monoclonal antibody (anti-p68).

A series of monoclonal antibodies was produced by immunization of mice with cells of the human promonocytic cell line CM-S; one of these recognized a membrane antigen (MW 68,000) constitutively expressed by these cells. Antigen p68 was also found to be expressed on all granulocytic cells and most mononuclear leukocytes from normal human peripheral blood, but not on hemopoietic precursor cells from bone marrow. Various types of leukemic cells also expressed antigen p68 as did various transformed human cell lines whether derived from hemopoietic cells or from other tissues. Antigen p68 is involved in T-lymphocyte regulation. In fact, the antibody anti-p68 has a strong synergistic effect increasing the proliferative response of peripheral blood T-lymphocytes both in the mixed lymphocyte reaction and when the lymphocytes are stimulated by suboptimal doses of lectin (phytohemagglutinin), tumor promoter phorbol esters, or tetanus toxoid. The anti-p68 antibody synergizes with the active metabolite of vitamin D3, 1,25-dehydroxyvitamin D3, to induce monocyte to macrophage maturation and enhances the function of mature granulocytes stimulated with the granulocyte-macrophage colony-stimulating factor in vitro.