A NOVEL MULTILINEAGE CELL-SURFACE ANTIGEN EXPRESSED ON TERMINALLY DIFFERENTIATED CHICKEN B-CELLS IN MUCOSAL TISSUES

A murine monoclonal antibody, 5M19, produced to a cell line transforme d by an avian myeloblastosis virus, detects an antigen, designated chL 5, that is expressed on multiple lineages of hematopoietic cells from noninfected chickens. Immunochemical analysis demonstrated the chL5 an tigen to be a homodimer of two disulfide-bonded chains each having an apparent molecular weight of 128,000. The highest level of expression was found on myelomonocytic cells, including granulocytes, monocytes, and macrophages, as well as on activated T lymphocytes and plasma cell s in mucosal tissues. A low level of chL5 expression is detectable on T lymphocytes in the thymus and peripheral tissues of juvenile chicken s, and mitogen activation of T lymphocytes results in a twofold increa se in antigen expression. By Day 15 of embryonic development chL5 is e xpressed by a small population (12%) of yolk sac cells and by the majo rity of mononuclear cells in the thymus, bone marrow, and spleen. Also , chL5(+) cells populate the embryonic bursa of Fabricius before the a ppearance of IgM(+) B lymphocytes. A novel characteristic of this anti gen is its expression on about 50% of plasma cells in the mucosal tiss ues of the Harderian gland and cecal tonsils while present on only 3-1 1% of circulating B cells and less than 2% of splenic plasma cells. Im mature B lymphocytes are negative for chL5 expression. Mitogen-induced activation and differentiation of peripheral B cells does not alter t he percentage of chL5(+) B cells. This antigen, therefore, is a useful marker for the analysis of terminal differentiation of B lymphocytes. The cell distribution of chL5 and the correlation of expression with cell aggregation in vitro suggests that the antigen may be involved in cell adhesion. (C) 1994 Academic Press, Inc.