The identification and developmental requirements of colonic <scp>CD</scp>169⁺ macrophages

Abstract

Summary CD 169‐positive macrophages in the marginal zone of the spleen and subcapsular sinus of lymph nodes play an important role as gatekeepers, strategically located to capture pathogens. Here we identified a population of CD 169‐positive macrophages in the colon and investigated which factors influenced their development. Murine colonic CD 115 + F4/80 lo CD 11c lo macrophages expressing CD 169 were present in the lamina propria, mainly surrounding the crypts. In spite of the high levels of bacterial flora in the colon and the importance of Toll‐like receptor signalling in mucosal homeostasis, the presence of CD 169 + macrophages was not affected in mice that were deficient in MyD88‐mediated Toll‐like receptor signalling and in mice in which the bacterial flora was eradicated. Whereas the development of splenic CD 169 + macrophages was dependent on lymphotoxin α , colonic CD 169 + macrophages were present in normal numbers in lymphotoxin α ‐deficient mice. In contrast, reduced numbers of CD 169 + macrophages were found in the colon of mice deficient in vitamin A, whereas CD 169 + macrophages in the spleen were unaffected. In conclusion, we identified a new macrophage subset in the lamina propria of the colon characterized by the expression of CD 169. Its differentiation, unlike CD 169 + macrophages in lymphoid organs, is independent of lymphotoxin α signalling, but requires vitamin A.