Sustained high expression of Fcγ receptorII (CD32) on dendritic cells (DCs) in patients with rheumatoid arthritis (RA)

Introduction

DCs are professional antigen presenting cells. For antigen internalisation, DCs use the Fcγ receptorII (CD32) which recognises anti-IgG-complexes and therefore might be involved in regulation of autoimmunity. Normally, CD32 is abundantly expressed on immature DCs and down-regulated after full maturation.

Objective

Evaluation of CD32 expression on DCs from RA patients.

Methods

Peripheral blood mononuclear cells obtained from RA patients and healthy donors were cultured with GM-CSF and IL-4 for 6 days to obtain immature DCs. Stimulation with LPS from day 6 yielded mature DCs at day 8. The expression of surface markers involved in T cell-DC interaction (DC-SIGN, CD83) antigen uptake (FcγRI, IIandIII) and presentation (CD80, CD86, MHC-I and MHC-II) were studied using FACS analysis. In addition, RT-PCR and in vivo colocalisation studies using DC-specific markers in synovium were used to confirm these findings.

Results

In both RA patients and controls DCs expressed expected levels of CD80, CD86, CD83, MHC-I, MHC-II and DC-SIGN. Interestingly, immature DCs showed a threefold increase in expression of CD32 when compared with controls (mean fluorescence 185.8 vs. 63.0 P < 0.01). Moreover, this increased expression of CD32 is sustained in fully mature DCs from RA patients (mean fluorescence 452.3 vs. 187.8 P = 0.005), whereas CD32 expression is strongly down-regulated upon maturation of DCs from controls. The sustained high expression of CD32 was further confirmed by RT-PCR. Both FcγRIIa and FcγRIIb were increased in immature DCs as well as mature DC from RA patients but not in DCs from healthy controls. In RA both immature and mature DCs showed a balance towards FcγRIIb. Colocalisation between FcγRII and DC-LAMP and DC-CK1 was clearly observed in RA synovial tissue.

Conclusion

Both immature and mature DCs from RA patients showed a significant increased expression of the FcγRII suggestive for an aberrant maturation pathway. In vivo, mature DCs with a high FcγRII expression are clearly present in the synovium in RA. These findings are suggestive for a crucial role of high FcγRII expression on DCs in synovial tissue in promoting and sustaining the local immune response in RA.