Association of Elevations of Specific T Cell and Monocyte Subpopulations in Rheumatoid Arthritis With Subclinical Coronary Artery Atherosclerosis

Abstract

Objective: Coronary artery disease (CAD) is the leading cause of excess deaths in rheumatoid arthritis (RA). However, identification of features denoting patients with a risk of developing CAD is lacking. The composition of circulating peripheral blood mononuclear cell (PBMC) subsets in RA patients differs markedly from that in healthy controls with regard to the extent of T cell activation, with clonal expansion and differentiation to effector memory status, and presence of inflammatory monocytes. In this study, we sought to evaluate whether elevations in these PBMC subpopulations in RA patients could denote those with an increased risk of subclinical CAD, as determined by the presence of coronary artery calcification (CAC).

Methods: The study cohort comprised 72 patients with RA who underwent cardiac computed tomography to assess CAC. PBMC subsets were determined by multiparameter flow cytometry. Multivariable logistic regression was used to determine the associations between PBMC subpopulations and the presence of CAC.

Results: Among the 72 patients with RA, 33% had CAC and exhibited significant increases in the levels of circulating CD4 T cell subsets denoting activation and differentiation to the effector memory phenotypes. Analogous increases in the levels of CD8 T cell subsets, as well as in the CD14(high)CD16+ intermediate monocyte subset, were also present in these patients, as compared to those without CAC. The increases in the CD4 and CD8 T cell subsets were highly intercorrelated, whereas the increases in CD14(high)CD16+ monocytes were independent of elevations in the CD4 T cell subsets. After adjustments for relevant confounders, the levels of CD4+CD56+CD57+ T cells and CD14(high)CD16+ monocytes remained associated with the presence of CAC.

Conclusion: These findings indicate that PBMC subsets are markers for the presence of CAC and suggest that mechanisms of atherogenesis in RA may operate in part through the elevations in these subsets, raising further questions about the mechanisms underlying the presence of such alterations in cell composition in patients with RA and the potential for shared etiologic pathways between RA and cardiovascular disease.

Figure 1. PBMC subsets in representative case, RA54, with increased memory effector T cells, intermediate monocytes and CAC

Panel A: distribution of CD28 expression on CD4⁺ and CD4(CD8) T cells on CD3 T cells. 41.5% (28.2 +13.3) of CD3⁺ T cells are CD4⁺, [%CD4⁺ (in CD3⁺)] and that 37.0% (100×13.3/(28.2 +13.3)) have extinguished CD28 expression, indicating memory phenotype differentiation [%CD28 (in CD4⁺)]. Panel B: s distribution of HLA-DR activation marker on CD28⁺ and CD28 CD4 cells. 10.3%(100×6.91/(6.9 +61.1)) of CD28⁺ and 13.6% (100×4.36/(4.36 +27.6)) of CD28 cells express HLA-DR, [%HLA-DR⁺ CD28 (in CD4⁺)]. Panel C: expression of NKR CD57 on CD4⁺ and CD4(CD8) T cells. 34.2% (100×14.4/(14.46 +27.7)) of CD4 T cells express CD57, [%CD57⁺ (in CD4⁺)]. Panel D: expression of NKR CD56 on CD4⁺ and CD4(CD8) T cells. 17.5%(100×7.33/(7.33 +34.6)) of CD4 T cells express CD56, [%CD56⁺ (in CD4⁺)]. Panel E: extent of coexpression of CD57 and CD56 on CD4 T cells. 72.7% (100×12.7/(12.7 +4.76)) of CD56⁺CD4⁺ T cells express CD57, [%CD57⁺ (in CD4⁺CD56⁺)]. Panel F: expression of subset markers, CD14 and CD16, on monocytes. 9.7% of CD14⁺ monocytes are intermediate CD14^hiCD16⁺ monocytes, Abbreviations: PBMC Peripheral Blood Mononuclear Cells, CAC Coronary Artery Calcification, NKR Natural killer cell receptor.

Figure 2. Crude and Adjusted Associations of the Proportions of % CD57⁺ (in CD4⁺ CD56⁺) and CD14^hiCD16+ Cells with the Probability of Any CAC

Crude associations are depicted by open circles. Adjusted associations are depicted with the solid least squares indicator and 95% confidence interval (light dashed line). Each unit increase in the square root of % CD57⁺ (in CD4⁺ CD56⁺) was associated with a 40% higher adjusted odds of any CAC (Panel a; p=0.046) while each unit increase in %CD14^hiCD16⁺ was associated with a 19% higher adjusted odds of any CAC (Panel b.; p=0.027). Adjustments for age, systolic blood pressure, and the other PBMC subset. Other RA and CVD risk factors were not retained in adjusted models as they were not associated with both the PBMC subsets of interest and the presence of CAC. ^*Abbreviations: PBMC Peripheral Blood Mononuclear Cells, CAC Coronary Artery Calcification, RA Rheumatoid Arthritis, CVD CardioVascular Disease, CD cluster designation, p probabiity, OR odds ratio.