Human T Lymphocyte Receptors for IgM: Reactivity with Monomeric 8S Subunit

Abstract

Up to 75% of T lymphocytes in human peripheral blood bear receptors for the Fc fragment of IgM which are easily detectable by a rosette assay (T.µ rosettes) ² (1, 2). These cells appear to belong to a subpopulation different from that of T lymphocytes with IgG Fc receptors, with distinct characteristics and functions (3, 4). IgM appears to bind to the T cell receptors by its C4 domain (5). The question of whether the receptor site on T cells binds monomeric IgM or not has important physiologic implications. In the present experiments, and in contrast to the conclusions of a previous report (6) that suggested specificity for pentameric IgM, we have found that unreduced monomeric 8S human IgM is a more effective inhibitor of T.µ rosette formation than pentameric 19S IgM. In another series of experiments, erythrocytes coated either with 8S or with 19S IgM antibodies were used for T.µ rosette formation and these experiments confirmed that monomeric IgM readily binds to the T cell receptors.