Thymic independence of the bone marrow lymphocyte phytohemagglutinin (PHA) response demonstrated in nude mice

Abstract

The phytohemagglutinin (PHA) response of lymphocytes from the bone marrow and lymph nodes of athymic, nude mice and their normal littermates was studied using a sensitive microculture assay system. Whereas the lymph node PHA response was virtually absent in nude mice, the bone marrow lymphocyte response to this phytomitogen was undiminished in the athymic mice at all concentrations of PHA and all incubation periods. As shown on radioautographs, the responding cells were morphologically identical with PHA-responsive lymphocytes of normal marrow and lymph node. The possibility of mature T cell contamination of the nude mice was ruled out by the observation that the nature of the PHA response of the nude bone marrow was identical with that of normal bone marrow lymphocytes, but was distinct from that of normal lymph node cells. The studies unequivocally demonstrate that the bone marrow response to PHA is independent of the thymus. A hypothesis is discussed which suggests that precursor T cells are responsible for the bone marrow PHA response, whereas mature T cells are primarily involved in the response of other lymphomyeloid organs to this mitogen.