Immunohistochemical study of immune cells in the bovine endometrium at different stages of the oestrous cycle.

Normal uteri were collected from 34 maiden heifers at slaughter and their stage of the oestrous cycle was determined from the ovarian structures. Cells expressing major histocompatibility complex (MHC) class II were widely distributed in the epithelium and lamina propria of the endometrium and were the most abundant population studied. The expression of MHC class II increased in the endometrium during the follicular phase of the cycle. Macrophages occurred throughout the stratum compactum and stratum spongiosum and their density did not appear to vary with the stage of the cycle. CD4+ cells were found mainly in the stratum spongiosum, whereas CD8+ cells were present mainly within the luminal and glandular epithelia and in the stratum compactum. The density of the populations of CD4+ and CD8+ cells increased markedly during the mid-to-late luteal and follicular phases, respectively, of the cycle. In the endometrium lymphoid aggregates were observed only rarely and no B cells were identified in any of the heifers.