CD56-expressing T cells that have features of senescence are expanded in rheumatoid arthritis

Objective. T cells deficient in CD28 expression have been implicated in the pathogenesis of rheumatoid arthritis (RA). Given that CD28-null T cells are functionally heterogeneous, we undertook this study to screen for novel receptors on these cells. Methods. Seventy-two patients with RA (ages 35-84 years) and 53 healthy persons (32 young controls ages 19-34 years, 21 older controls ages 39-86 years) were recruited. Phenotypes and proliferative capacity of T cells from fresh leukocytes and of long-term cultures were monitored by flow cytometry. Lung biopsy specimens from patients with RA-associated interstitial pneumonitis (IP) were examined by immunohistochemistry. Receptor functionality was assessed by crosslinking bioassays. Results. Chronic stimulation of CD28+ T cells in vitro yielded progenies that lacked CD28 but that gained CD56. Ex vivo analysis of leukocytes from patients with extraarticular RA showed a higher frequency of CD56+,CD28-null T cells than in patients with disease confined to the joints or in healthy controls. CD56+,CD28-null T cells had nil capacity for proliferation, consistent with cellular senescence. CD56+ T cells had skewed T cell receptor (TCR) α/β-chain usage and restricted TCR third complementarity-determining region spectra. Histologic studies showed that CD56+ T cells were components of cellular infiltrates in RA-associated IP. CD56 crosslinking on T cells sufficiently induced cytokine production, although CB56/TCR coligation induced higher production levels. Conclusion. Chronic activation of T cells induces counterregulation of CD28 and CD56 expression. The loss of CD28 is accompanied by the gain of CD56 that confers TCR-independent and TCR-dependent activation pathways. We propose that accumulation of CD56+ T cells in RA contributes to maladaptive immune responses and that CD56+ T cells are potential targets for therapy.