Prevention of diabetes in non-obese diabetic mice by a single immunization with Mycobacterium leprae.

The incidence of overt diabetes was completely prevented by a single intradermal inoculation of Mycobacterium leprae (M. leprae) into Non-obese diabetic (NOD) mice as young as 6-7 weeks. Partial prevention was also observed in cases when 65 kD heat-shock protein (hsp65) with Freund's incomplete adjuvant (FIA) was injected, and no prevention was observed by 38 kD with FIA immunization. Histological examination of pancreata demonstrated that control and M. leprae-immunized mice at 24 weeks of age developed the insulitis even though the number of lymphocytes infiltrated in the treated ones were less than the controls. However, later, at 47 weeks of age, even the immunized mice become to develop very severe insulitis. Thus, M. leprae-immunization did not prevent the incidences of insulitis. The spontaneous development of serum antibody against hsp65 and 38 kD protein preceded the onset of diabetes in NOD mice. Lymphocytes response, IFN-gamma and IL-10 production of splenocytes cultures stimulated with hsp65 were examined to clue the reasons for the prevention of IDDM incidence by M. leprae immunization. The spontaneous development of anti-hsp65 T lymphocytes preceded the outbreak of overt IDDM in control NOD mice, but also appeared in M. leprae immunized cases in which the IDDM incidence was prevented, and both control and M. leprae immunized groups produced IFN-gamma and IL-10 by stimulation with hsp65.