A morphological and immunohistochemical study of lymphoid germinal centers in synovial and lymph node tissues from rheumatoid arthritis patients with special reference to complement components and their receptors

Rheumatoid arthritis (RA) is one of the immune complex (IC) diseases in which lymphoid germinal centers (GCs) are found in the synovial tissue. Simultaneously, patients with RA often show swelling of lymph nodes. The morphology and function of the lymph-node GCs in patients with RA is not clear. The aim of this study was to evaluate the differences in morphology and immunoreactions to complement (C) components, their receptors, and IgM-rheumatoid factor (RF) between synovial GCs and lymph-node GCs in RA. Furthermore, the relationship between these immunoreactive substances and follicular dendritic cells (FDCs) in GCs was investigated. The tissues examined were 41 RA synovial specimens, seven RA lymph nodes with massive lymphadenopathy, and 10 non-RA lymph nodes. The number of synovial GCs was relatively decreased in comparison with lymph-node GCs in RA, and the diameter of each synovial GC was smaller than that of each lymph-node GC. The synovial GCs were edematous and less cellular, and moreover, those from RF-seronegative cases were smaller than those from RF-seropositive cases. On the other hand, the lymph-node GCs in RA were larger, more cellular and hyperplastic, but contained more tingible-body macrophages (TBMs) and neutrophils. In the GCs of both synovial tissues and lymph nodes in RA, early C components (C1q, C4, C3c, C3d), IgM-RF, and C3b receptor (C3bR) and C3d receptor (C3dR) were expressed as a lacy network by light microscopy, and were demonstrated on the surfaces of FDCs and lymphocytes, and in the intercellular spaces by electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)