Differential survival of leukocyte subsets mediated by synovial, bone marrow, and skin fibroblasts: Site‐specific versus activation‐dependent survival of T cells and neutrophils

Objective Synovial fibroblasts share a number of phenotype markers with fibroblasts derived from bone marrow. In this study we investigated the role of matched fibroblasts obtained from 3 different sources (bone marrow, synovium, and skin) to test the hypothesis that synovial fibroblasts share similarities with bone marrow–derived fibroblasts in terms of their ability to support survival of T cells and neutrophils. Methods Matched synovial, bone marrow, and skin fibroblasts were established from 8 different patients with rheumatoid arthritis who were undergoing knee or hip surgery. Resting or activated fibroblasts were cocultured with either CD4 T cells or neutrophils, and the degree of leukocyte survival, apoptosis, and proliferation were measured. Results Fibroblasts derived from all 3 sites supported increased survival of CD4 T cells, mediated principally by interferon‐β. However, synovial and bone marrow fibroblasts shared an enhanced site‐specific ability to maintain CD4 T cell survival in the absence of proliferation, an effect that was independent of fibroblast activation or proliferation but required direct T cell–fibroblast cell contact. In contrast, fibroblast‐mediated neutrophil survival was less efficient, being independent of the site of origin of the fibroblast but dependent on prior fibroblast activation, and mediated solely by soluble factors, principally granulocyte–macrophage colony‐stimulating factor. Conclusion These results suggest an important functional role for fibroblasts in the differential accumulation of leukocyte subsets in a variety of tissue microenvironments. The findings also provide a potential explanation for site‐specific differences in the pattern of T cell and neutrophil accumulation observed in chronic inflammatory diseases.