Retention of Immune Complexes by Fc Receptors on Mouse Follicular Dendritic Cells

Abstract

Follicular dendritic cells (FDC) are located inside lymph follicles and are mainly characterized by their capacity to retain antigens. We investigated this aspect in mice lymph nodes by using bovine serum albumin (BSA) labelled with 5-nm colloidal gold particles and homologous anti-BSA antibodies bound to 20-nm gold particles. Gold-labelled BSA injected alone in non-immunized mice was only rarely found in FDC cytoplasmic interdigitations. Injected in the form of immune complexes, it was retained by FDC. Antigen-free anti-BSA antibodies injected under similar conditions as immune complexes were always found in draining lymph nodes in the same locations as BSA-anti-BSA immune complexes. F(ab')2 from mouse immunoglobulins linked to colloidal gold particles were very rarely found between the FDC extensions, whereas it was intensely phagocytosed by macrophages. Our study permitted precise ultrastructural localization between FDC cytoplasmic extensions or inside macrophages and other cells of the lymph nodes, but it also pointed out that homologous antibodies linked to colloidal gold particles might be retained by FDC in the absence of antigens. These observations, carried out with colloidal gold, were checked by using 125I-labelled anti-BSA antibodies. Complement activation determinations of gold-labelled antibodies or immune complexes showed that antibodies or immune complexes fixed on colloidal gold particles do not activate the complement. This observation enabled us to conclude that Fc receptors play a significant part in the retention of gold-labelled antibodies or immune complexes by FDC of lymph nodes.

Fcγ Receptor IIB on Follicular Dendritic Cells Regulates the B Cell Recall Response

“…and C4b (CR1/2) (18 -20) and the Fc receptors for IgG ICs (Fc␥R) (22,23,35). These receptors are expressed on both B cells and FDCs; however, given our results and those of others, their function on each cell type is apparently quite different.…”

“…This prompted the speculation that one function of the FDC is to convert the poorly immunogenic ICs to a form capable of stimulating potent B cell responses (17). Complement and complement receptors appear to be important for trapping of ICs by FDC (18 -20), and several studies have suggested that Fc receptors for IgG are also involved (21)(22)(23) Mice express three FcRs for IgG: Fc␥RI, Fc␥RII, and Fc␥RIII. Fc␥RI and Fc␥RIII are associated with the common FcR ␥-chain and trigger cellular activation responses upon cross-linking, while Fc␥RIIB is a monomeric inhibitory receptor, modulating activation responses when coligated to an immunoreceptor tyrosinebased activation motif (ITAM)-containing receptor such as the B cell receptor (BCR) complex.…”

Patterns of age‐dependent changes in the numbers of lymph follicles and germinal centres in somatic and mesenteric lymph nodes in growing C57Bl/6 mice

“…FDCs express Fc receptors and complement receptors (C3 receptors) on their surfaces, and are therefore able to bind immune complexes (Gerdes & Stein, 1982 ;Radoux et al 1985 ;Reynes et al 1985 ;Yoshida et al 1993 ;van den Berg et al 1995, Imai et al 1998. These receptors are thus useful immunocytochemical markers of FDCs.…”

Morphological Changes in the Mouse Popliteal Lymph Node after Local Injection of Dextran Sulfate

“…It is possible that injected DS may have caused disorganization of preexisting follicles by affecting FDC in the follicle stromata. FDC have the capacity to hold immune complexes (IC), since they possess Fc and C3 receptors capable of binding IC (Klaus and Humphrey 1977;Radoux et al 1985). If FDC in the pre-existing follicles were in fact affected by DS, the treated nodes would be unable to bind IC in the peripheral cortex.…”

“…. 16. Electron micrograph of the outer layer of the peripheral cortex in a popliteal node at 3 days after a 500-,ug injection of DS.…”