B lymphocytopenia in rheumatoid arthritis is associated with the DRB1 shared epitope and increased acute phase response

Abstract

The influence of HLA DRB1 alleles on B-cell homeostasis was analyzed in 164 patients with rheumatoid arthritis (RA). The percentages of CD19+ B lymphocytes determined in the peripheral circulation of 94 retrospectively recruited RA patients followed a bimodal distribution. Two frequency peaks (B-cell(low) patients and B-cell(high) patients) were separated by the population median of a B-cell frequency of 8.5% of all lymphocytes. Human leucocyte antigen genotyping revealed that the B-cell(low) patients were more frequently positive for the RA-associated HLA DRB1 shared epitope (SE) than were B-cell(high) patients. Accordingly, SE-positive patients had lower CD19 percentages in the rank-sum analysis when compared with SE-negative patients, and were markedly B lymphocytopenic when compared with a healthy control group. To confirm the differential frequencies of CD19+ B cells, absolute numbers in peripheral blood were determined prospectively in a cohort of 70 RA patients with recent onset disease. SE-positive patients were found to have lower absolute numbers of circulating CD19+ B cells. B-cell counts below the mean of the study population were associated with higher acute phase response and with increased levels of rheumatoid factor IgA. No correlation between absolute numbers of circulating B cells and radiographic progression of joint destruction was seen. The influence of immunogenetic parameters on B-cell homeostasis in RA reported here has not been described previously. The clinical relevance of B lymphocytopenia in SE-positive RA will be further investigated in longitudinal studies.

Figure 1

(a) Histogram depicting the distribution of B-cell frequencies in the peripheral circulation from 94 rheumatoid arthritis (RA) patients. The percentage of CD19⁺ cells from total peripheral lymphocytes is plotted on the x axis, and the number of patients in each frequency range is plotted on the y axis. The overlays represent the Gaussian frequency distributions fitted to the two populations. (b) Percentage of CD19⁺ B cells in the peripheral circulation in patients negative (SE-) and positive (SE+) for the RA-associated shared epitope and in age-matched healthy controls. Bars depicts mean and standard error of the mean. ^*P = 0.05 compared with healthy controls, ^**P = 0.02 compared with healthy controls, ^***P < 0.001 compared with SE-positive RA patients.

Figure 2

B-cell counts in the peripheral circulation of 70 prospectively followed rheumatoid arthritis (RA) patients determined after a mean disease duration of 4.4 years. Absolute numbers of CD19⁺ B cells are depicted to exclude shifts in the B-cell/T-cell ratio of patients expressing the RA-associated shared epitope on a DR4 allele (SE DR4⁺), of patients expressing DR1 but not a RA-associated DR4 allele (SE DR1⁺), and of patients negative for the SE (SE-negative). Box plots depict the median and interquartile range.

Figure 3

Comparison of (a) C-reactive protein (CRP) levels, (b) rheumatoid factor (RF) IgM titers, and (c) RF IgA titers in patients below (CD19_low) and above (CD19_high) the mean of the study population (110 B cells/ml), which was determined after a mean disease of 4.4 years. The different time points of observation are indicated on the x axis, starting from the first visit in the rheumatology clinic. All graphs depict the mean and standard error of the mean. ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.