Dendritic cells (DC) are professional antigen-presenting cells with the unique ability to stimulate naïve T cells and to trigger strong immune responses. However, DC have also shown tolerogenic ability in several systems under certain conditions, depending on their differentiation/activation status. In particular, treatment of DC with cAMP-elevating agents promotes impaired dendritic cell maturation and inhibition of T-cell responses, therefore providing a potential therapy for autoimmune disorders.
Our objective was to study the effect of cholera toxin (CTx)-treated DC in the development of mouse collagen-induced arthritis (CIA), a well-established animal model of rheumatoid arthritis. CTx was chosen because it maintains sustained high cAMP levels by irreversibly binding to adenylate cyclase.
Arthritis was induced by intradermal injection of 200 μg bovine type II collagen (bCII) in complete Freund's adjuvant in the base of the tail of male DBA/1 mice. Bone marrow-derived DC, loaded with bCII (50 μg) and treated with CTx (1 μg/ml), were injected at the time of immunization. Arthritis incidence and severity was assessed for 21 days following arthritis onset. For in vitro analysis of the effect of DC in T-cell activation, lymph nodes from bCII-immunized mice were collected before arthritis onset and stimulated with CTx-treated DC. Proliferation and interferon gamma production were determined by thymidine incorporation and capture ELISA, respectively.
Injection of CTx-treated DC resulted in a decreased arthritis incidence (Fig. 1) and reduced severity, compared with non-DC treated animals. This effect required the combination of CTx and antigen specificity, as DC treated with CTx in the absence of bCII, as well as non-treated DC in the presence of bCII, did not show a significant reduction in the incidence of arthritis. Furthermore, treatment with DC alone results in an acceleration of disease progression.
Figure 1. Arthitis incidence in bovine type II collagen (CII)–complete Freund's adjuvant immunized mice injected with cholera toxin (CTx)-treated dendritic cells (DC).
In vitro analysis of T-cell responses revealed that Ctx-treated DC were able to inhibit both proliferation and interferon gamma production from lymph nodes of immunized mice. Interestingly, this inhibition was not antigen specific, as it was also observed in the absence of bCII, suggesting that additional mechanisms are involved in the reduced arthritis incidence observed in vivo.
In summary, our data indicate that manipulation of dendritic cell activity with cAMP-elevating agents provides a therapeutic tool for the treatment of antigen-specific autoimmune disorders.