Lethal Mycobacterium bovis Bacillus Calmette Guerin infection in nitric oxide synthase 2-deficient mice: Cell-mediated immunity requires nitric oxidesynthase 2

The role of nitric oxide (NO) in Mycobacterium bovis Bacillus Calmette Guer in (BCG) infection was investigated using nitric oxide synthase 2 (nos2)-de ficient mice, because NO plays a pivotal protective role in M. tuberculosis infection. We demonstrate that nos2-deficient mice were unable to eliminat e BCG and succumbed within 8 to 12 weeks to BCG infection (10(6) CFU) with cachexia and pneumonia, whereas all infected wild-type mice survived. The g reatest mycobacterial loads were observed in lung and spleen. Nos2-deficien t mice developed large granulomas consisting of macrophages and activated T cells and caseous necrotic lesions in spleen. The macrophages in granuloma s from nos2-deficient mice had reduced acid phosphatase activities, suggest ing that NO is required for macrophage activation. The absence of NOS2 affe cted the cytokine production of the Th1 type of immune response, except IL- 18. Serum amounts of IL-12p40 were increased and IFN-gamma was decreased co mpared with wild-type mice. The lack of NOS2 resulted in an overproduction of TNF, observed throughout the infection period. Additionally, TNFR1 and T NFR2 shedding was altered compared with wild-type mice. Up-regulation of TN F may be compensatory for the lack of NOS2. The late neutralization of TNF by soluble TNF receptors resulted in heightened disease severity and accele rated death in nos2-deficient mice but had no effect in wild-type mice. In conclusion, the inability of nos2-deficient mice to kill M. bovis BCG resul ted in an accumulation of mycobacteria with a dramatic activation of the im mune system and overproduction of pro-inflammatory cytokines, which resulte d in death.