Distribution of macrophages in the mouse uterus from one day to three months after parturition, as defined by the immunohistochemical localization of the macrophage-restricted antigens F4/80 and macrosialin.

Abstract

The morphology of placental detachment sites and the distribution of macrophages were studied in the mouse uterus from day 1 to 3 months post partum. Uterine morphology was studied using H&E and Mallory's Trichrome staining. Macrophages were identified using the macrophage-restricted antigens F4/80 and FA/11 and the leukocyte beta 2-integrin CR3 (Mac-1) which is also expressed by neutrophils. The post-partum wound was infiltrated by large numbers of CR3+ F4/80+ FA/11+ macrophages, and CR3+ neutrophils. The wound resolved rapidly and no inflammatory infiltrate or necrotic tissue was seen by day 5 post partum. The area of the detachment wound and the site of the metrial gland of pregnancy resolved into a structure, here called a post-partum nodule, which persisted for at least three months. The post-partum nodule consisted of an outer layer of collagen around a group of nodule-specific cells which could be divided into haemosiderin- and lipid-bearing phenotypes. The lipid-bearing nodule cells were not found after day 20 post partum. Nodule cells were FA/11+ at all times and also expressed leukocyte common antigen. Expression of CR3 and F4/80 was found on nodule cells up to day 9-10 post partum. CR3 expression was found only occasionally after day 10. F4/80 expression was downregulated from day 9-10 to day 20 but was found consistently after day 20. Implantations of second and subsequent pregnancies are known not to occur in the immediate vicinity of post-partum nodules and nodules from successive pregnancies were seen to be separate within the uterus. Since the endometrial area in the immediate vicinity of nodules is inimical to implantation and nodules consist of a group of macrophages, it can be implied that nodule macrophages are exerting some influence on the endometrium in their vicinity.