Dysregulated intracellular Ca2+ stores and Ca2+ signaling in synovial fluid T lymphocytes from patients with chronic inflammatory arthritis

Objective. Peripheral blood (PB) T cells from rheumatoid arthritis (RA) pat ients proliferate poorly to mitogen, a change that is related to decreased intracellular Ca2+ ([Ca2+](i)) signaling after T cell receptor (TCR) stimul ation, We hypothesized that this was, in part, due to the effect of mediato rs of inflammation and predicted that greater changes in [Ca2+](i) signalin g would be seen in synovial fluid (SF) T cells. We also examined the mechan isms underlying the altered [Ca2+](i) signals. Methods, Paired PB and SF T cells from patients with chronic inflammatory a rthritis were stimulated with mitogen to assess the magnitude of the [Ca2+] (i) signal in cell populations by fluorometry, the pattern of the [Ca2+](i) signal in individual cells in a single-cell ion-imaging system, and the sp atial distribution of Ca2+ within intracellular organelles. Results. There was a significantly smaller [Ca2+](i) signal after phytohema gglutinin protein stimulation of SF T cells (peak rise in [Ca2+](i) signal PB versus SF 200 nM versus 180 nM; P < 0.05), In single SF T cells, a chang e in the pattern of the [Ca2+](i) signal and a reduction in the number of r esponding cells was seen. These changes were a magnification of those seen in RA PB compared with control PB T cells. The contribution of Ca2+ release from intracellular stores to the final [Ca2+](i) signal in PB and SF T cel ls was equal, but there was a significant increase in the Ca2+ remaining in the endoplasmic reticulum (ER) in SF T cells after TCR activation (PB vers us SF 6 nM versus 19 nM; P < 0.05). Non-ER Ca2+ stores were not similarly a ffected. Conclusion. We found abnormalities in the magnitude, pattern, and spatial distribution of [Ca2+](i) signaling in T cells from SF of patients with chronic inflammatory arthritis. A reduction in the number of respondin g SF T cells may partly explain some of our observations. However, we propo se that the observed redistribution of SE Ca2+ stores may underlie the alte red [Ca2+](i) signaling, thus making these cells hyporesponsive to mitogen. The inflammatory environment of the joint and the late stage of differenti ation of SF T cells are both likely to contribute to these changes in [Ca2](i) signaling, resulting in aberrant T cell function and promotion of dise ase chronicity.