THE PROINFLAMMATORY CYTOKINE INTERLEUKIN-12 OCCURS AS A CELL MEMBRANE-BOUND FORM ON MACROPHAGES

Phagocyte-derived interleukin-12 (IL-12) is a proinflammatory cytokine promoting cell-mediated immune responses in inflammatory and infectio us disorders. Based on sequence homology of the p40 subunit with the i nterleukin-6 receptor it has been speculated that IL-12 could also exi st as a membrane-bound form, but thus far only soluble (secreted) IL-1 2 has been identified. We have therefore analyzed human monocytic U937 and mouse P388D, macrophages for membrane-bound IL-12 by how cytometr y. IL-12 is constitutively expressed on the cell surface of both cell lines. IL-12 cell surface staining is enhanced in response to stimulat ion with IFN-gamma plus LPS. IL-12 is also present in the supernatant of cultured P388D, macrophages. Thus, in addition to a soluble form IL -12 occurs as a membrane-bound molecule on monocyte/macrophage cell li nes. (C) 1996 Academic Press, Inc.