CCR6 + Th cell populations distinguish ACPA positive from ACPA negative rheumatoid

Introduction: Patients with rheumatoid arthritis (RA) can be separated into two major subpopulations based on the absence or presence of serum anti-citrullinated protein antibodies (ACPAs). The more severe disease course in ACPA + RA and differences in treatment outcome between these subpopulations suggest that ACPA + and ACPA � RA are different disease subsets. The identification of T-helper (Th) cells specifically recognizing citrullinated peptides, combined with the strong association between HLA-DRB1 and ACPA positivity, point toward a pathogenic role of Th cells in ACPA + RA. In this context we recently identified a potential pathogenic role for CCR6 + Th cells in RA. Therefore, we examined whether Th cell population distributions differ by ACPA status. Methods: We performed a nested matched case-control study including 27 ACPA + and 27 ACPAtreatment-naive early RA patients matched for disease activity score in 44 joints, presence of rheumatoid factor, sex, age, duration of complaints and presence of erosions. CD4 + CD45RO + (memory) Th cell distribution profiles from these patients were generated based on differential chemokine receptor expression and related with disease duration. Results: ACPA status was not related to differences in total CD4 + T cell or memory Th cell proportions. However, ACPA + patients had significantly higher proportions of Th cells expressing the chemokine receptors CCR6 and CXCR3. Similar proportions of CCR4 + and CCR10 + Th cells were found. Within the CCR6 + cell population, four Th subpopulations were distinguished based on differential chemokine receptor expression: Th17 (CCR4 + CCR10 � ), Th17.1 (CXCR3 + ), Th22 (CCR4 + CCR10 + ) and CCR4/CXCR3 double-positive (DP) cells. In particular, higher proportions of Th22 (p = 0.02), Th17.1 (p = 0.03) and CCR4/CXCR3 DP (p= 0.01) cells were present in ACPA + patients. In contrast, ACPA status was not associated with differences in Th1 (CCR6 � CXCR3 + ; p = 0.90), Th2 (CCR6 � CCR4 + ; p = 0.27) and T-regulatory (CD25 hi FOXP3 + ; p = 0.06) cell proportions. Interestingly, CCR6 + Th cells were inversely correlated with disease duration in ACPApatients (R 2 =�0.35; p < 0.01) but not in ACPA + (R 2 < 0.01; p = 0.94) patients. Conclusions: These findings demonstrate that increased peripheral blood CCR6 + Th cells proportions distinguish ACPA + RA from ACPARA. This suggests that CCR6 + Th cells are involved in the differences in disease severity and treatment outcome between ACPA + and ACPARA.