Regulatory T-cell defect in the arthritis-susceptible DBA/1 mouse

Background

DBA/1 mice are susceptible to collagen-induced arthritis and to low-grade spontaneous inflammatory arthritis in elderly males. CD4⁺CD25⁺ T cells have been implicated in the suppression of arthritis in the susceptible DBA/1 strain [1, 2] and in patients with rheumatoid arthritis [3]. We have studied the function of the CD4⁺CD25⁺ T-cell subset in DBA/1 and arthritis-non-susceptible C57Bl/6 male mice.

Methods

The frequencies of CD4⁺CD25⁺ T cells were assessed in lymph nodes and the spleen of DBA/1 and C57Bl/6 mice by FACS analysis. Spleens were harvested from adult male DBA/1 and BALB/c mice. CD4⁺CD25⁺ and CD4⁺CD25^- T cells were purified using Miltenyi reagents and a VarioMACS. Proliferation assays in response to either Concanavalin A (1 μg/ml) or soluble anti-CD3 (0.1–10 μg/ml) were performed using 5e4 CD4⁺CD25^- cells with 1e5 irradiated adherent splenocytes as antigen-presenting cells. Co-culture of CD4⁺CD25⁺ and CD4⁺CD25^- T cells in a 1:1 ratio was used to assess suppression. Cytokines (IL-2, interferon gamma, IL-4, IL-10, tumour necrosis factor alpha, IL-6, IL-17, IL-15) were measured in the tissue culture supernatant after 36 hours incubation. Proliferation was measured by [³H]-thymidine incorporation. Suppression ratios (SRs) were calculated as follows: SR = (response from CD25⁺:CD25^- T-cell coculture) / (response from CD25^- T cells alone). SRs in DBA/1 and C57Bl/6 mice were compared using Student's t test.

Results

The frequency of CD4⁺CD25⁺ T cells was comparable in the spleen and lymph nodes of DBA/1 and C57Bl/6 mice. SRs were higher (i.e. less suppression) in proliferation assays from DBA/1 mice compared with C57Bl/6 mice, which were stimulated with anti-CD3 (P = 0.03). DBA/1 cultures were generally associated with higher cytokine levels. Cytokine SRs were higher (i.e. less suppression) for DBA/1 compared with C57Bl/6 cultures for IL-6 and IL-17. SRs were lower (i.e. more suppression) for DBA/1 compared with C57Bl/6 cultures for IL-4 and IL-10.

Conclusions

The arthritis-susceptible DBA/1 mouse strain appears to have a functional defect in the CD4⁺ CD25⁺ T-cell compartment. IL-4 and IL-10 are efficiently suppressed by CD4⁺CD25⁺ T cells. Suppression of IL-6 and IL-17 appears to be defective. This may partly explain the susceptibility of DBA/1 mice to erosive arthritis.