The molecular chaperone BiP (GRP 78) inhibits the differentiation of normal human monocytes into immature dendritic cells

Objective

To evaluate the effects of BiP, which has recently been shown to prevent collagen-induced arthritis, on the differentiation of monocytes into immature dendritic cells (IDCs).

Methods

Monocytes from healthy blood donors were cultured for 3 days with GM-CSF and IL-4 to generate IDCs, either alone or in the presence of BiP (20 μg/ml) or β-galactosidase (20 μg/ml) as a control. TNF-α and IL-10 levels were measured by ELISA from the culture supernatants collected at 24 and 72 hours. Neutralisation experiments with IL-10 blockers were performed. Immunoflurescent staining and FACS analysis were carried out on cells harvested at day 3. Mixed leukocyte reactions were performed by coculturing the different monocyte populations with purified allogenic T cells (ratio 1:10) for 5 days.

Results

Addition of BiP to monocytes cultured with GM-CSF and IL-4 i) significantly inhibited down-regulation of CD14 and up-regulation of HLA-DR, CD80, CD86 and CD1a, the pattern of surface markers usually consistent with IDC differentition, ii) induced a significantly higher production of IL-10 within the supernatants and iii) strongly inhibited the proliferation of allogeneic T cells. Many of the effects mediated by BiP can be reversed by the addition of anti-IL10 antibody.

Conclusion

These findings support the concept that BiP may have immunomodulatory properties that could have therapeutic benefit in rheumatoid arthritis.