The role of macrophages in the removal of apoptotic B-cells in the sheep ileal Peyer's patch.

In the process of generating the cells that populate the sheep's B-cell pool, the ileal Peyer's patch (PP) produces an immense number of B-cells and then destroys most of them by apoptosis. Rapid clearance of these apoptotic cells is essential for tissue homeostasis and for preventing pathology. Macrophages comprise a small percentage of cells in the follicles. They resemble macrophages found in other tissues and can be identified by the expression of MHC Class II and CD14. In this study, enriched macrophages co-cultured with apoptotic ileal PP cells showed increased DNA content as they ingested apoptotic cells. The higher the proportion of apoptotic cells in culture the greater the increase in DNA content of the macrophages. This occurred when B-cell apoptosis was initiated by a period in culture or in response to treating the animals with steroids. Thus, macrophages resident in the ileal PP follicle mediate the phagocytosis and removal of discarded B-cells.