Phenotypic subpopulations of macrophages and dendritic cells in human spleen

Using immunohistochemical techniques and a large number of monoclonal antibodies, the presence and distribution of phenotypic subpopulations of macrophages (MOs) and dendritic cells in human spleen were assessed. The results of this study show that different subsets of MOs and dendritic cells are present in the spleen and that some of these occupy discrete microanatomic locations. In the red pulp (RP) certain antigens are expressed by different proportions of uniformly distributed MOs in the cords. On the other hand, some antigens are present on MOs that form clusters of variable size within the red pulp. These include CD11c, CD15 and alpha-1-anti-chymotrypsin. Another type of cell in the RP that is phagocytic under certain conditions is the splenic sinusoidal lining cell (SLC). These cells exhibit a phenotype that is unique: nonspecific esterase (NSE)+, lysozyme+, and HLA-DR+, CD36+, factor VIII-related antigen+, CD8+ and CD71+. MOs in the splenic marginal zone (MZ) share some antigens with red pulp MOs, but in addition express CD11b, CD14 (Mo2;63D3) and 61D3. These antigens are found on only a few RP MOs. MZ cells expressing one antigen shared with RP MOs (CD4) and one present largely on the MZ cells (CD14;63D3) form clusters around small vessels; these structures resemble the so-called splenic ellipsoids that may play a role in the trapping of circulating antigens. Phagocytic MOs (tangible body MOs) of the white pulp follicular germinal centers were also shown to differ from RP and MZ cells with respect to the expression of the antigens CD11b, CD14 (Leu M3;Mo2), CD16 and the antigen detected by antibody 25F9. The unique topographical and surface antigenic features of dendritic cells were confirmed by this study. Furthermore, these cells were found to share a number of antigens with RP, MZ, and white pulp MOs, which suggests that they may be derived from a common progenitor. The presence of phenotypic subpopulations and variation in distribution among human splenic phagocytic cells and dendritic cells may be indicative of functional specialization.