Immunoregulatory effect of anti-thymocyte globulin monotherapy on peripheral lymphoid tissues of non-obese diabetic mice.

Objective: Experimental and clinical studies have shown that autoimmunity-causing diabetes may be abrogated by immune intervention. Several anti-T-lymphocyte antibodies focus on distinct T-cell targets. We tested the effect of murine anti-thymocyte globulin (ATG; Genzyme, Framingham, MA) in peripheral lymphoid organs of non-obese diabetic (NOD) mice after the onset of hyperglycemia.

Methods: Diabetic NOD mice were treated with two doses of ATG (1 mg totally) or maintained without treatment as controls. Blood glucose levels were monitored twice a week. The mice were terminated at day 0, 7, 14, or 28 after the initiation of the study. Subpopulations of T-lymphocytes and FoxP3+ (forkhead box P3 positive) regulatory T-cells were analyzed among elements isolated from the spleen and pancreatic lymph nodes.

Results: Mice with blood glucose levels greater than 13 mmol/L were included in the study. Diabetes remission occurred in 16% (3/19) of mice treated with ATG. Only one case of remission was observed in the control group (6%; 1/16). ATG therapy a significantly decreased the CD8+/CD4+ T-lymphocyte ratio. Among splenocytes, a significant difference was detected only on day 7 (0.069 versus 0.198 T-lymphocyte ratio); in lymph nodes, a decrease was observed on day 28 (0.21 versus 0.51 T-lymphocytes ratio). The regulatory T-cells population increased after ATG administration compared with the control group at day 7 (16.2% versus 10.8% in CD4+ splenocytes; 20.7% versus 10.3% in CD4+ lymph node cells). However, the increased FoxP3+ cell population was not durable.

Conclusions: ATG treatment of diabetic NOD mice showed an immunoregulatory effect in peripheral lymphoid tissue with a significantly deceased CD8+/CD4+ ratio, which, however, did not normalize the metabolic parameters in a short period after the onset of overt diabetes.