Inhibition of Type 1 Diabetes in Filaria-infected Non-obese Diabetic Mice is Associated with a T Helper Type 2 Shift and Induction of FoxP3+ Regulatory T Cells

We sought to determine whether Litomosoides sigmodontis, a filarial infection of rodents, protects against type 1 diabetes in non-obese diabetic (NOD) mice. Six-week-old NOD mice were sham-infected or infected with either L3 larvae, adult male worms, or adult female worms. Whereas 82% of uninfected NOD mice developed diabetes by 25 weeks of age, no L. sigmodontis-infected mice developed disease. Although all mice had evidence of ongoing islet cell inflammation by histology, L. sigmodontis-infected mice had greater numbers of total islets and non-infiltrated islets than control mice. Protection against diabetes was associated with a T helper type 2 (Th2) shift, as interleukin-4 (IL-4) and IL-5 release from alpha-CD3/alpha-CD28-stimulated splenocytes was greater in L. sigmodontis-infected mice than in uninfected mice. Increased circulating levels of insulin-specific immunoglobulin G1, showed that this Th2 shift occurs in response to one of the main autoantigens in diabetes. Multicolour flow cytometry studies demonstrated that protection against diabetes in L. sigmodontis-infected NOD mice was associated with significantly increased numbers of splenic CD4(+) CD25(+) FoxP3(+) regulatory T cells. Interestingly, injection of crude worm antigen into NOD mice also resulted in protection against type 1 diabetes, though to a lesser degree than infection with live L. sigmodontis worms. In conclusion, these studies demonstrate that filarial worms can protect against the onset of type 1 diabetes in NOD mice. This protection is associated with a Th2 shift, as demonstrated by cytokine and antibody production, and with an increase in CD4(+) CD25(+) FoxP3(+) regulatory T cells.