Mycobacteria Precipitate Autoimmune Rheumatic Disease in NOD Mice Via an Adjuvant-Like Activity

NOD mice spontaneously develop organ-specific autoimmunity and are widely used as a model for diabetes. NOD mice also exhibit some features of non-organ specific autoimmune rheumatic disease such as thymocytotoxic and anti-nuclear autoantibodies and they develop haemolytic anaemia in senescence. A single dose of 2.6x10⁷ heat-killed Bacillus Calmette-Guerin (BCG) i. v. in 8-week-old NOD mice prevented diabetes but precipitated a syndrome similar to systemic lupus erythematosus (SLE), in which treated mice rapidly developed haemolytic anaemia, high litre anti-DNA and anti-Sm antinuclear autoantibodies, perivascular lymphocytic infiltration in the kidneys and glomerular immune complex deposition. Here, we examined the mechanism of action by which BCG precipitated rheumatic autoimmune disease in NOD mice. Two weeks after injection, reticuloendothetial cell function was dramatically increased in BCG-treated NOD mice. By 4 weeks, treated mice had a three- to four-fold increase in Mac-1⁺ and class-II⁺, B220-negative splenocytes and in vitro antigen-presentation capacity was enhanced two- to four-fold. In vivo responses to SRBC confirmed enhancement of DTH 4 weeks after BCG injection, consistent with an adjuvant-like activity.