Synovial cellular and molecular markers in rheumatoid arthritis

Abstract

The profound alterations in the structure, cellular composition, and function of synovial tissue in rheumatoid arthritis (RA) are the basis for the persistent inflammation and cumulative joint destruction that are hallmarks of this disease. In RA, the synovium develops characteristics of a tertiary lymphoid organ, with extensive infiltration of lymphocytes and myeloid cells. Concurrently, the fibroblast-like synoviocytes undergo massive hyperplasia and acquire a tissue-invasive phenotype. In this review, we summarize key components of these processes, focusing on recently-described roles of selected molecular markers of these cellular components of RA synovitis.

Figure 1. Strong expression of CD13 in RA synovium

CD13 (green) in RA synovium, co-localized (yellow) with cadherin-11 (red), a marker of FLS. CD13 is also extensively expressed on monocyte-macrophage lineage cells in RA synovial tissue, which do not express cadherin-11.

Figure 2. A Dense Infiltrate of Activated T Cells in RA Synovium

The CD30 molecule (upper right panel) is expressed on activated T and B lymphocytes, and the CD3 complex (lower left panel) is present on all T cells. CD30, which is found on a very small proportion of circulating lymphocytes, is expressed by >90% of the synovial T cells. The lower right panel, showing merged red and green fluorescence which generates a yellow color, indicates that the great majority of the CD30+ cells in the RA synovium are T cells. The blue color is DAPI, which identifies nuclei.