Increased Expression and Modulated Regulatory Activity of Coinhibitory Receptors PD ‐1, TIGIT , and TIM ‐3 in Lymphocytes From Patients With Systemic Sclerosis

Objective Immune dysfunction is an important component of the disease process underlying systemic sclerosis ( SS c), but the mechanisms contributing to altered immune cell function in SS c remain poorly defined. This study was undertaken to measure the expression and function of the coinhibitory receptors (co‐ IR s) programmed cell death 1 ( PD ‐1), T cell immunoglobulin and ITIM domain ( TIGIT ), T cell immunoglobulin and mucin domain 3 ( TIM ‐3), and lymphocyte activation gene 3 ( LAG ‐3) in lymphocyte subsets from the peripheral blood of patients with SS c. Methods Co‐ IR expression levels on subsets of immune cells were analyzed using a 16‐color flow cytometry panel. The functional role of co‐ IR s was determined by measuring cytokine production after in vitro stimulation of SS c and healthy control peripheral blood mononuclear cells ( PBMC s) in the presence of co‐ IR –blocking antibodies. Supernatants from cultures of stimulated PBMC s were added to SS c fibroblasts, and their impact on fibroblast gene expression was measured. Mathematical modeling was used to reveal differences between co‐ IR functions in SS c patients and healthy controls. Results Levels of the co‐ IR s PD ‐1 and TIGIT were increased, and each was coexpressed, in distinct T cell subsets from SS c patients compared to healthy controls. Levels of TIM ‐3 were increased in SS c natural killer cells. PD ‐1, TIGIT , and TIM ‐3 antibody blockade revealed patient‐specific roles of each of these co‐ IR s in modulating activation‐induced T cell cytokine production. In contrast to healthy subjects, blockade of TIGIT and TIM ‐3, but not PD ‐1, failed to reverse inhibited cytokine production in SS c patients, indicating that enhanced T cell exhaustion is present in SS c. Finally, cytokines secreted in anti– TIM ‐3–treated PBMC cultures distinctly changed the gene expression profile in SS c fibroblasts. Conclusion The altered expression and regulatory capacity of co‐ IR s in SS c lymphocytes may contribute to disease pathophysiology by modulating the cytokine‐mediated cross‐talk of immune cells and fibroblasts at sites of inflammation and/or fibrosis.