Background/Purpose: Follicular T helper (Tfh) cells, a CD4 T helper subset localized in lymphoid organs, help B cell differentiation and function. Circulating CD4 T cells expressing CXCR5 together with ICOS and/or PD-1 are considered as counterparts of Tfh, can function as B cell helpers, and can be subdivided into three subpopulations based on the expression of CCR6 and/or CXCR3: CXCR5+CXCR3+CCR6- (Tfh-Th1), CXCR5+CXCR3-CCR6+ (Tfh-Th17) and CXCR5+CXCR3-CCR6- (Tfh-Th2). Only Tfh-Th17 and Tfh-Th2, as opposed to Tfh-Th1, seem to display functional properties of Tfh cells. An altered proportion of these subpopulations has been associated with autoimmune diseases. Terefore, our objective was to study the frequency of circulating Tfh and Tfh cell subsets together with the frequency of circulating plasmablasts (CD19+CD20-CD27+CD38high B cells) in patients with Rheumatoid Arthritis (RA).

Methods: Peripheral blood was drawn from healthy controls (n=27) and RA patients (n=27). After isolation by Ficoll- Hypaque gradient, PBMCs were stained with antibodies to CD3, CD4, CXCR5, ICOS, PD-1, CCR6, CXCR3, CD19, CD20, CD27, and CD38, and examined by flow cytometry. The percentages of CXCR5+CXCR3+CCR6- (Tfh-Th1), CXCR5+CXCR3- CCR6+ (Tfh-Th17) and CXCR5+CXCR3-CCR6- (Tfh/Th2) cells were calculated after gating for CD3, CD4 and CXCR5+. The percentage of CD20-CD38high cells was calculated after gating for CD19+ and CD27+.

Results: The frequency of circulating CXCR5+ cells gated for CD4+ T cells was not different among the studied groups. In contrast, RA patients demonstrated an increased frequency of CD4+CXCR5+ICOS+PD-1+ cells. Furthermore, in RA patients, the frequency of Tfh-Th1 cells was significantly decreased and the frequency of Tfh-Th17 and Tfh-Th2 cells was significantly increased as compared with controls. Subsequently, the ratio (Tfh-Th17+Tfh-Th2)/Tfh-Th1 was increased in RA patients. When examining seropositive (RF+ and/or ACPA+) and seronegative RA patients (RF- and ACPA-) separately, it was evident that the above described alterations were only apparent in seropositive RA. That is, seropositive but not seronegative RA patients demonstrate a higher proportion of Tfh subsets bearing a phenotype associated with B cell helping capacity. At the same time, the frequency of circulating plasmablasts was increased in seropositive but not in seronegative RA. Interestingly, there was a significantly positive correlation between the percentage of circulating plasmablasts and the frequency of CXCR5+ICOS+PD-1+CD4+ T cells. In addition, the frequency of circulating plasmablasts showed a positive correlation with the ratio (Tfh-Th17+Tfh-Th2)/Tfh-Th1.

Conclusion: Seropositive, but not seronegative RA patients, demonstrate an increased frequency of circulating Tfh counterparts (CXCR5+ICOS+PD-1+CD4+ T cells) and altered proportions of circulating Tfh subpopulations, with overrepresentation of subsets bearing a phenotype associated with B cell helping capacity. At the same time, an increased proportion of circulating plasmablasts is apparent in seropositive RA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/an-altered-frequency-of-circulating-follicullar-t-helper-cell-counterparts-and-their-subsets-is-associated-with-increased-circulating-plasmablasts-in-seropositive-ra-patients/