Graft-versus-host reactions in mice. 3. Epithelioid and multinucleated giant cells of thymic origin.

Thymus cells from C3H donor mice were infused into lethally irradiated (C3H x C57BL/10)F(1) hybrid mice. Light and electron microscopic examination of the lymphoid tissues of recipients revealed the presence of epithelioid and multinucleated giant cells in addition to lymphocytes and histiocytes. Serial transplantation of thymus-derived cells into irradiated F(1) hybrid mice resulted in a preponderance of epithelioid cells over lymphocytes. Epithelioid cells, as well as lymphocytes and histiocytes, incorporated (3)H-thymidine, indicating that they were actively proliferating. Following transplantation of CBA-T6T6 thymocytes into irradiated (C3H x C57BL/10)F(1) mice, karyotypic analysis of host lymphoid tissues indicated that all dividing cells were of donor origin. Whereas bone marrow is known to give rise to epithelioid cells in the absence of thymic influences, the thymus must also contain precursors of epithelioid cells.