Monocytes confer CD14 antigenicity on activated lymphocytes

In the present study, exposure of human peripheral blood mononuclear cells (PBMC) to phorbol 12-myristate 13-acetate (PMA) was found to elicit the expression of CD14 on lymphocytes. Less than 3% of the lymphocytes present among freshly isolated PBMC were stained with 63D3 anti-CD14 monoclonal antibody (mAb). Within two days of exposure of PBMC to PMA, up to 30% of the lymphocytes reacted with the 63D3 anti-CD14 mAb, though not with the LeuM3 and My4 anti-CD14 mAbs. The appearance of CD14 on lymphocytes was also elicited by exposure of PBMC to phytohemagglutinin (PHA), concanavalin A (Con A), or agarose-bound phytohemagglutinin but not by exposure to lipopolysaccharide, interferon-α, or interleukin-2. Purified lymphocyte preparations did not acquire CD14 following stimulation with PMA. Monocytes lost their reactivity with CD14 mAbs (63D3, LeuM3, and My4) within a few hours after exposure to PMA. The level of soluble CD14 was higher in supernatant fluids of cultures of untreated PBMC than of PMA-stimulated PBMC. The addition of PMA to cultures of T cells and monocytes separated by Millipore filters lead to the expression of CD14 on the lymphocytes. The present study indicates that activation of lymphocytes in the presence of monocytes leads to the appearance of CD14 on lymphocytes, and raises the possibility that the expression of CD14 on lymphocytes may result from the transfer of CD14 molecules from monocytes to lymphocytes.