Histological and functional differentiation of non-lymphoid cells in the chicken spleen

The phenotypes and functions of various populations of non-lymphoid cells in the chicken spleen were investigated with monoclonal antibodies and after in vivo administration of antigens. Monoclonal antibody CVI-ChNL-68.1 was used to detect red pulp macrophages, interdigitating cells, and monocytes, whereas CVI-ChNL-68.2 was used to detect ellipsoid-associated non-lymphoid cells (EANC). Two new monoclonal antibodies were developed: CVI-ChNL-74.2, which specifically recognized red pulp macrophages and a ring of macrophages surrounding the peri-ellipsoid lymphocyte sheath; and CVI-ChNL-74.3, which specifically recognized follicular dendritic cells (FDC) in germinal centres and small clusters of stromal cells in T-cell areas. After intravenous injection of lipopolysaccharide (LPS), the number of 68.1+ and 74.2+ macrophages decreased dramatically, whereas 68.2+ EANC and 74.3+ FDC were unaffected. After intravenous injection of heat-inactivated Brucella abortus, the numbers of both macrophages and EANC decreased. In contrast, a significant increase of 74.3+ cells was observed in the T-cell areas outside the germinal centres. As expected, intravenous injection of non-mitogenic antigens, such as keyhole limpet haemocyanin and Ficoll, and carrageenan did not affect the non-lymphoid cell populations. At least six subpopulations of non-lymphoid cells in the chicken spleen can now be discriminated with monoclonal antibodies. Our results show that mononuclear phagocytes are sensitive for mitogenic stimulators such as LPS and Brucella abortus. In contrast, stromal non-lymphoid cells are only sensitive to the particulate mitogen Brucella abortus. We conclude that the complex formed by ellipsoid cells, the peri-ellipsoid B-cell sheath, and the surrounding macrophages, is the functional equivalent of the mammalian marginal zone.