Monoclonal Antibodies against Leucoagglutinin‐Reactive Human T‐Lymphocyte Surface Components

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Abstract
A monoclonal antibody, K46M (IgM .vkappa.), obtained after immunization with leucoagglutinin (La)-reactive T-cell surface components, stimulated human lymphocytes to proliferate. It induced maximal proliferation at > 20 .mu.g IgM/ml after 3-4 days of culture. Cells stimulated by K46M produced interleukin 2 (IL-2) and gamma interferon (IFN-.gamma.) and expressed receptors for IL-2 and transferrin. The majority of the activated cells were phenotypically T cells as defined by monoclonal antibodies against CD3 and CD2, and an increase in the K46M-positive cells was also observed during the activation period. K46M-activated cells display major histocompatibility complex (MHC)-unrestricted cytotoxicity against several cultured target cells. The frequencies of the cytotoxic and of the proliferative precursor cells were determined using a limiting dilution assay. K46M seems to activate a larger fraction of cytotoxic precursor cells against Molt 4 than against K562, but the statistical significance of these observations requires further exploration. Both K46M or La activated 40% of PBL to proliferate, whereas 70% of PBL were induced by OKT3. However, the frequency of K46M-activated cells was 40% only when the lymphocytes were plated at low cell densities, i.e. < 0.5 cells per well. At higher densities an inhibition of proliferation was seen that resulted in a biphasic response curve, indicating that the activation of PBL by K46M was not a single hit event. This was not found with either La or OKT3. Whether K46M, in contrast to OKT3 and La, activates a subpopulation with suppressor activity remains to be established.

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