Reduced expression of the complement receptor type 2 (CR2, CD21) by synovial fluid B and T lymphocytes

Abstract

The expression of CR2 (CD21) by synovial B and T lymphocytes of patients suffering from various forms of arthritis was analysed with cytofluorometry and with reverse transcriptase-polymerase chain reaction. CR2 (CD21) cell surface protein was detected in normal quantities on peripheral B cells, but was almost absent on synovial B lymphocytes of the same patients. This reduction was most severe in patients with rheumatoid arthritis, but also observed in all other cases. CR2 (CD21) did not reappear after in vitro culture. CR2 (CD21) mRNA was also strongly reduced in synovial B and T lymphocytes. Synovial fluid B lymphocytes were larger than peripheral blood B lymphocytes, while T cells from the same patients showed no size differences. We conclude that synovial fluid B lymphocytes have undergone an irreversible step towards terminal differentiation. The presence or absence of CR2 (CD21) mRNA in peripheral versus synovial T cells indicates that CR2 (CD21) is also differentially expressed by T lymphocytes.

Fig. 1

Expression of CR2 (CD21) on the surface of peripheral blood (PB) and synovial fluid (SF) B lymphocytes from patients with rheumatoid arthritis (RA) or reactive arthritis (ReA). PB mononuclear cells (MNC) and SF MNC were stained with anti-CD19–PE and anti-CR2 (CD21)–FITC MoAbs. Depicted are eight representative examples of lymphocytes from RA patients (a) and patients with ReA (b).

Fig. 2

Ratios of the mean fluorescence intensities (MFI) of CR2 (CD21) on CD19⁺ peripheral blood (PB) and synovial fluid (SF) B lymphocytes. Individual values are given for patients with rheumatoid arthritis (RA; •) or reactive arthritis (ReA; ○). MFI averages of CR2 (CD21) expression (black bars) on PB B lymphocytes were 3·5 ± 0·8 (RA) and 3·0 ± 0·7 (ReA).

Fig. 3

(See previous page.) Stability of CR2 (CD21) expression by synovial and peripheral B lymphocytes in vitro. Peripheral blood (PB) mononuclear cells (MNC) and synovial fluid (SF) MNC of rheumatoid arthritis (RA) patients were analysed directly after isolation, or after in vitro culture for 48 h in medium containing 5% fetal calf serum.

Fig. 4

Reduction of CR2 (CD21) mRNA in synovial but not peripheral blood lymphocytes of the same patients. Equal amounts of RNA were reverse transcribed into cDNA and used to amplify the transmembrane region of CR2 (CD21). GAPDH primers were used to show that equal amounts of cDNA were used for each polymerase chain reaction. The patients suffered from rheumatoid arthritis (lanes 1 and 5), reactive arthritis (lane 2), psoriasis arthritis (lane 3) or unclassified polyarthritis (lane 4).

Fig. 5

Size of synovial fluid B and T lymphocytes in comparison with peripheral blood (PB) cells. Mean forward scatters of lymphocytes expressing either CD19 (a) or CD4 or CD8 (b) were calculated. (a) Peripheral blood and synovial B cells from rheumatoid arthritis (RA) patients (□ and ▪, respectively) and reactive arthritis (ReA) patients (○ and Δ, respectively) are depicted. (b) Mean forward scatter from RA patients' CD4⁺ and CD8⁺ T cells from PB (□ and ○) and synovial fluid (▪ and Δ, respectively) display the same average.