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) patients proliferate poorly to mitogen, a change that is related to decreased intracellular Ca2+ ([Ca2+]i) signaling after T cell receptor (TCR) stimulation. We hypothesized that this was, in part, due to the effect of mediators of inflammation and predicted that greater changes in [Ca2+]i signaling would be seen in synovial fluid (SF) T cells. We also examined the mechanisms underlying the altered [Ca2+]i signals.


METHODS
Paired PB and SF T cells from patients with chronic inflammatory arthritis 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 spatial distribution of Ca2+ within intracellular organelles.


RESULTS
There was a significantly smaller [Ca2+]i signal after phytohemagglutinin 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 change in the pattern of the [Ca2+]i signal and a reduction in the number of responding 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 cells 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 versus SF 6 nM versus 19 nM; P < 0.05). Non-ER Ca2+ stores were not similarly affected.


CONCLUSIONS
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 responding SF T cells may partly explain some of our observations. However, we propose that the observed redistribution of SF Ca2+ stores may underlie the altered [Ca2+]i signaling, thus making these cells hyporesponsive to mitogen. The inflammatory environment of the joint and the late stage of differentiation 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 disease chronicity.
Carruthers
D M
DM
Department of Rheumatology, University of Birmingham, UK.
Arrol
H P
HP
Bacon
P A
PA
Young
S P
SP
D001172:Arthritis, Rheumatoid / Q000097:blood / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002908:Chronic Disease; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D015388:Organelles / Q000378:metabolism; D012016:Reference Values; D013582:Synovial Fluid / Q000166:cytology / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007476:Ionophores; D015759:Ionomycin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium