Mechanism of follicular trapping: double immunocytochemical evidence for a contribution of locally produced antibodies in follicular trapping of immune complexes.

Using two different antigen-enzyme conjugates and a double immunocytochemical staining technique, we demonstrate the localization patterns of two different specific antibodies in the same spleen section. During the early immune responses against simultaneously injected human gamma globulin (HGG), and bovine gamma globulin (BGG) in rabbits, the localization patterns of extracellular anti-HGG antibodies and extracellular anti-BGG antibodies in the follicles overlap only partly. It was shown in earlier studies that extracellular antibodies trapped in the follicles represent antigen-antibody complexes having free binding sites for the antigen. The fact that localization patterns do not overlap extensively, whereas it has been shown in earlier studies that follicular dendritic cells (FDCs) show no specificity with respect to the immune complexes to be captured, leads to the following conclusion. After formation of immune complexes from antibody molecules released by specific antibody-forming cells in the follicles and antigen present in excess between the cells, part of these complexes are trapped by adjacent FDCs. Results are discussed with respect to the possible role of follicular immune complexes in the generation of immunological memory.