Binding of IgM by human T lymphocytes.

Ox erythrocytes, sensitized with IgM-type rabbit antibodies, were found to form rosettes with human blood lymphocytes. Granulocytes, monocytes, and macrophages appeared to lack this property. The rosette formation could be inhibited with human IgM and its Fc fragments. IgM-binding lymphocytes were also present in cell suspensions isolated from human tonsils and thymuses and among blood lymphocytes cultured in vitro. The outcome of combined marker tests and cell separation experiments disclosed that the rosetting lymphocytes belong to the T-lymphocyte population.