Dysregulation of Inhibitory Receptor Expression in Systemic Sclerosis

Abstract

Systemic sclerosis (SSc) is an autoimmune connective tissue disorder associated with aberrant fibrosis of the skin and internal organs that can lead to organ failure and death in patients. With few treatment options many patients succumb to fibrosis of the lungs or kidneys, or due to vascular damage culminating in pulmonary disease; the 50 percent survival rate is only about 10 years. We collected PBMCs from 36 SSc patients that were not on immune-suppressants, along with 25 age-matched healthy controls. Using a 15 color flow cytometry panel our lab has observed increases in the inhibitory receptors PD-1, TIGIT, and Tim-3 on PBMCs from SSc patients. This increase in expression is cell type specific with PD-1 and TIGIT shown to be increased on defined T cell types including CD4+ T cells, both Treg and non-Treg subsets, as well as CD8+ T cells. Tim-3 was only statistically significantly increased on a mature subset of CD16+ CD56med natural killer cells. This increase was not seen for all inhibitory receptors. The expression of LAG-3 remained low across all cell types observed. This increase in inhibitory receptor expression was enhanced in patients with a high percent of Tregs within the CD4+ gate. In vitro blockade of these inhibitory receptors provided differential cytokine secretion in patients versus healthy subjects, suggesting a possible role in disease pathogenesis. The observation of increased inhibitory receptors in SSc as well as the ability to modulate cytokines by blocking the interaction of these receptors with their ligands could provide insights into possible immune modulation in patients.