Functions of multinucleated giant cells formed by fusing rat alveolar macrophages with lymphokines containing macrophage fusion factor.

Rat alveolar macrophages (AM) fused and formed multinucleated giant cells (MGC) when incubated with lymphokines released from mitogen-stimulated syngeneic lymphocytes. Several functions of these MGC populations were evaluated in vitro. MGC populations phagocytized opsonized sheep red blood cells to a lesser degree than unfused AM. The tumoricidal activity of MGC populations was compared with that of unfused AM after both populations had been treated with lipopolysaccharide (LPS) or lymphokines devoid of fusion factor activity. Results showed that MGC populations lost tumoricidal properties more rapidly than unfused AM. Treatment of MGC with LPS enhanced the production and release of lymphocyte-activating factor(s) (IL-1, interleukin 1) that augmented the blastogenic response of lymphocytes to phytohemagglutinin. These studies suggest that one possible function of MGC that lack phagocytic and tumoricidal properties may be in maintenance of granuloma formation by IL-1 production.