Dendritic cells (DC) play an important role for initiation and regulation of immune response. Recent experimental evidence points out the fact that immature dendritic cells (iDC) can mediate tolerance, presumably by the induction of regulatory T cells. Therefore, we explored the effects of iDC injection on the development of collagen-induced arthritis in mice and compared them with tumour necrosis factor-matured DC, which we were previously shown efficient in collagen-induced arthritis.

Murine bone marrow-derived DC where cultured in the presence of GM-CSF and IL-4 for 6 days and were incubated or not for 24 hours with bovine type II collagen (bCII). The immature phenotype of DC was controlled by flow cytometry, IL-12p40 secretion and MLR assays. The iDC were repetitively injected 7, 5 and 3 days before arthritis induction with bCII. Mice were boosted on day 21 and the disease course was monitored until day 50. Paw swellings were measured over time, and radiological and histological analyses of paws were performed at euthanasia. The antigen-specific T-cell proliferative response of spleen cells, the Th1/Th2 cytokine production, and the serum levels of IgG₁/IgG_2a anti-bCII antibodies were measured.

The repetitive injection of tumour necrosis factor alpha-modulated DC loaded with bCII protects the mice from severe arthritis. This protective effect is antigen dependent of the DC loading with bCII. The immunosuppressive effect is associated with a decrease of the anti-bCII antibodies from the IgG_2a isotype, together with the inhibition of interferon gamma synthesis and the decrease proliferation of bCII-specific T cells.

Our data show that repetitive injection of immature unloaded DC protects the animals significantly as 70% of the mice did not develop clinical signs of the disease. We quantitated the various regulatory populations in the vaccinated mice, and observed in the liver and spleen an increase of the T-cell population expressing the CD49b molecule (DX5 cells). The relevance of this population in induced protection is under investigation.

The use of iDC to modulate the autoimmune response is a rational approach for cell therapy in diseases such as rheumatoid arthritis.