Background The systemic autoimmune rheumatic diseases (SARD; Systemic Lupus Erythematosus, Rheumatoid Arthritis, Sjogren's Disease, Systemic Sclerosis) are proposed to have a prolonged period of pre-clinical autoimmunity culminating in clinical disease. Evidence from disease-specific studies (e.g., SLE, RA) suggests that the pre-clinical phase is marked by the accrual of immunological abnormalities such as pathogenic auto-antibodies (auto-Ab). Little is known about the cellular derangements that accompany the transition from benign to pathological autoimmunity. Abnormalities in T cell subsets including invariant NKT (iNKT) and T follicular helper (TFH) cells are implicated in the development of systemic autoimmunity. Both a decrease in iNKT cells and an increase in TFH cells are found in patients with established SARD.
Objectives To determine if T cell abnormalities associated with SARD are present in pre-clinical autoimmunity.
Methods Patients (n=87) who were ANA+ (titer ≥1:160) and healthy controls (HC, n=37) were recruited. Patients were stratified into clinical subsets: (1) no defining SARD symptoms (n=24); (2) undifferentiated connective tissue disease (UCTD, n=17), one or more SARD defining symptom; and (3) early SARD (n=46), fulfilling ACR criteria for a SARD diagnosis. Patients were immunosuppressive and steroid naïve. PBMCs were isolated over a Ficoll gradient, stained with combinations of fluorescently labeled antibodies and analyzed by flow cytometry. ANA titer and auto-Ab profile were determined.
Results A statistically significant decrease in the proportion of iNKT cells (CD3+Vα24Jα18 TCR+) was found for all ANA+ patients relative to HC (p=0.0001). Similar results were found for each patient subset when compared to HC; ANA+ asymptomatic (p=0.001), UCTD (p=0.02) and SARD (p=0.001), with no differences amongst groups. The proportion of TFH (CD4+CXCR5highPD-1high) cells was significantly elevated (p=0.01) in patients versus HC. While the proportion of TFH cells was similar between asymptomatic ANA+ patients and HC, there was a significant expansion of TFH in UCTD as compared to both groups (p=0.02 and p=0.04, respectively). SARD patients had a non-significant trend to increased proportions of TFH as compared to UCTD. Patients (n=50) with higher ANA titers (≥1:640) had a significant increase (p=001) in TFH when compared to individuals (n=13) with lower ANA levels (1:160). A positive correlation (p<0.0001) between the proportion of TFH and the number of auto-Abs within the patient population was found. No significant differences were noted in the iNKT or TFH cell proportions between SARD patients stratified by specific disease diagnosis.
Conclusions A decrease in the iNKT cell subset is present at the earliest phase of pre-clinical autoimmunity (asymptomatic ANA+) suggesting that loss of this T cell subset contributes to a breach of tolerance to nuclear antigens. In contrast, increases in the TFH compartment appear to parallel the onset of clinical symptoms and accrual of auto-Abs. These results suggest that an incremental development of T cell abnormalities marks the progression towards clinically significant autoimmunity.
Disclosure of Interest None declared
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