Receptors for IgA on human lymphocytes. II. Organ distribution and relationships with other Fc receptor-bearing populations.

Lymphocyte populations expressing receptors for IgA (RFc alpha) in several human lymphoid tissues were numerically evaluated using a highly sensitive and specific indicator system. The percentages of RFc alpha-bearing lymphocytes were, in thymus, 9%; bone marrow, 14%; tonsil, 38%; cord blood, 34%; and adult blood, 55%. In adult and cord blood, RFc alpha were primarily associated with the T-lymphocyte populations as defined by their ability to bind sheep erythrocytes (SE). A large percentage of the peripheral T-lymphocyte population expressed both RFc alpha and receptors for IgM (RFcmu), whereas few T lymphocytes expressing receptors for IgG also displayed RFc alpha. Although a small number of peripheral non-T cells also expressed RFc alpha, they appeared to have fewer or less avid receptors than the RFc alpha-bearing T lymphocyte population. Both bone marrow and tonsil lymphocytes of both T and non-T populations expressed RFc alpha. Furthermore, the RFc alpha-bearing non-T population in both tonsil and bone marrow was quite large, 39 and 26%, respectively. These studies document the ubiquity of RFc alpha and its expression on the same peripheral lymphocyte population as RFcmu and indicate that RFc alpha is associated with several functionally different lymphocyte subpopulations including those involved in regulation (help) and antibody-dependent cell cytotoxicity.