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 transformed by an avian myeloblastosis virus, detects an antigen, designated chL5, that is expressed on multiple lineages of hematopoietic cells from noninfected chickens. Immunochemical analysis demonstrated the chL5 antigen 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 cells in mucosal tissues. A low level of chL5 expression is detectable on T lymphocytes in the thymus and peripheral tissues of juvenile chickens, and mitogen activation of T lymphocytes results in a twofold increase in antigen expression. By Day 15 of embryonic development chL5 is expressed by a small population (12%) of yolk sac cells and by the majority of mononuclear cells in the thymus, bone marrow, and spleen. Also, chL5+ cells populate the embryonic bursa of Fabricius before the appearance of IgM+ B lymphocytes. A novel characteristic of this antigen is its expression on about 50% of plasma cells in the mucosal tissues of the Harderian gland and cecal tonsils while present on only 3-11% of circulating B cells and less than 2% of splenic plasma cells. Immature B lymphocytes are negative for chL5 expression. Mitogen-induced activation and differentiation of peripheral B cells does not alter the 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.