Interleukin-12 gene expression is associated with rapid development of diabetes mellitus in non-obese diabetic mice

A single dose of cyclophosphamide (250 mg/kg) is known to synchronize and accelerate development of diabetes in non-obese diabetic mice. We have reported previously that cyclophosphamide treatment of 10-week-old female non-obese diabetic mice induces a shift from T-helper type 2 to T-helper type 1 activity in islet lesions. We now show that this shift in regulatory T-cell function is preceded by the expression of interleukin-12 in the islets as well as in the spleen. In the spleen macrophages were identified as the interleukin-12 expressing cell type. At the same time there was little induction of tumour necrosis factor alpha gene expression by macrophages. Since interleukin-12 is well known to drive T-helper cell type 1 responses we assume that interleukin-12 released by macrophages mediates the accelerating effect of cyclophosphamide on islet inflammation in non-obese diabetic mice. mRNA expression of the p40 chain of interleukin-12 in response to cyclophosphamide was not seen in macrophages of Balb/c mice and thus represents an immune abnormality of non-obese diabetic mice favouring T-helper type 1 reactions.