The role of various compartments in the chicken spleen during an antigen-specific humoral response.

In the chicken spleen, certain aspects of the complex of ellipsoid, peri-ellipsoid lymphocyte sheath (PELS), and ring of macrophages are morphologically and functionally similar to the marginal zone in the mammalian spleen. In this study, the role of this marginal zone-like complex was examined during the humoral immune response against a thymus-dependent antigen. The antigen peroxidase-conjugated rabbit anti-peroxidase (PAP) was injected intravenously in chickens and subsequently visualized by its enzymatic activity. Anti-PAP antibody-containing cells (ACC) were detected by incubation with PAP and subsequent peroxidase staining. Shortly after injection, PAP antigen was located in the ellipsoids. Within 24 hr most PAP had relocated to the B lymphocytes of the PELS. After this, most PAP disappeared, although minute amounts of PAP were detected in peri-arteriolar T-cell areas (PALS). At 48 hr, the PALS contained the first anti-PAP ACC; later ACC were also located in the red pulp. During the immune response, the isotype of the ACC switched from IgM to IgG. From 72 hr, PAP antigen and anti-PAP antibodies were trapped on follicular dendritic cells in immature and mature germinal centres. These results demonstrate that humoral immune responses are induced by the interaction of the PALS and the complex of ellipsoid, PELS and macrophages. These results, along with earlier ones, suggest that this complex is analogous to the marginal zone in the mammalian spleen.