Ia antigen expression in the rat uterus

Using indirect immunofluorescence and monoclonal antibodies, we have determined the distribution of Ia^- cells in the non-pregnant rat uterus. In cycling animals, Ia⁺ cells, most of dendritic shape and non-specific esterase negative, were abundant in the connective tissue of the myometrium and throughout the endometrium, especially adjacent to the luminal and glandular epithelia. In contrast, the number of T lymphocytes was very much less and few of these cells expressed Ia antigen. Stromal Ia⁺ cells were more numerous during estrus than in any other phase of the cycle. Only a few Ia⁺ cells were seen in neonatal uterine samples, but the numbers increased to approximately adult levels by 32 days of age. Prepubertal glands were consistently negative, but epithelial expression of Ia antigens in adult uteri showed interesting variations. The luminal epithelium was always negative, whereas the glandular epithelial cells often were positive. Glandular staining was quite heterogeneous in individual samples, but most gland profiles were negative or weakly positive during proestrus and estrus and positive during diestrus. Ovariectomized females given different steroid supplements revealed significant hormonal effects. Estrogen alone dramatically increased the numbers of Ia⁺ stromal cells compared with control samples, but progesterone alone had no effect. However, progesterone given with estrogen abrogated the estrogenic influence. Progesterone alone caused decreased expression of Ia antigens by the glandular epithelium. If the highly-Ia⁺ cells in the stroma are capable of antigen presentation, these results indicate a significant potential for local antigen processing within the uterine endometrium.