Marginal zone B cells regulate antigen capture by marginal zone macrophages.

The marginal zone (MZ) of the mouse spleen contains macrophages that express receptors that trap pathogens, including the scavenger receptor macrophage receptor with a collagenous structure and the C-type lectin specific intracellular adhesion molecule-grabbing nonintegrin receptor 1 (SIGN-R1). We previously reported that expression of SIGN-R1 was decreased in CD19-deficient mice. In this study, we demonstrate that SIGN-R1 is expressed on a subset of macrophage receptor with a collagenous structure (MARCO)(+) macrophages. This subset is diminished when MZ B cells are absent due to either genetic developmental defects or following transient migration of B cells out of the MZ. When B cells return to the MZ, there is a delay in recovery of SIGN-R1-expressing macrophages. During this period, capture of Ficoll, which for the macrophages requires SIGN-R1, remains defective not only by the macrophages, but also by the B cells. Thus, MZ B cells regulate expression of molecules on macrophages that are important for trapping Ag, which, in turn, is required for Ag capture by the B cells.