Formation of multinucleated giant cells from human monocyte precursors. Mediation by a soluble protein from antigen-and mitogen-stimulated lymphocytes.

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Abstract
Human lymphocytes when stimulated by specific antigens or T cell mitogens produce a soluble factor that causes peripheral blood monocytes to fuse and form multinucleated giant cells in vitro. Production of the giant cell factor by antigen-stimulated peripheral blood lymphocytes correlates with the existence of cell-mediated immunity to specific antigen. Monocyte-depleted blood lymphocytes, but not purified blood monocytes, produce the giant cell factor when cultured with antigens or T cell mitogens. Gel filtration and physicochemical studies indicate that the lymphocyte-derived giant cell factor is a heat-labile protein of .apprx. 60,000 MW. Multinucleated giant cells in granulomas may be formed by fusion of circulating monocytes in response to the release of a 60,000 MW protein from antigen-stimulated T lymphocytes.