Identification of a unique lymphocyte subpopulation in the sheep uterus

A panel of monoclonal antibodies was used to define the lymphocyte subpopulations in the sheep uterus at various stages of the oestrous cycle. A striking finding was that the majority of lymphocytes in the uterine and endometrial glandular epithelia belonged to a unique lymphocyte subpopulation that expressed the CD45R antigen but was negative for major histocompatibility complex (MHC) class II molecules and expressed low or undetectable levels of the CD5 antigen. When examined under the electron microscope using the immunogold technique, the CD45R+ lymphocytes were found to have one to three membrane-bound granules in their cytoplasm. Other lymphocyte subpopulations found in the uterus at various stages of the oestrous cycle were localized mainly in the caruncular and intercaruncular stroma. The unique CD45R+ granular lymphocyte subpopulation may be equivalent to the 'natural killer' cells reported in mouse and man, and may have an important role in local immunity of the female reproductive tract.