Effect of diesel exhaust particulate on bacillus Calmette-Guerin lung infection in mice and attendant changes in lung interstitial lymphoid subpopulations and IFNγ response

Abstract

The effect of exposure to diesel exhaust particulate (DEP) on bacillus Calmette-Guerin (BCG) lung infection in mice was studied. C57Bl/6J female mice were infected with BCG (2.5×10⁴ bacteria/mouse) by intrapulmonary instillation, with or without coadministration of DEP (100 µ g/mouse). Five weeks later, mice exposed to DEP + BCG had about a four-fold higher BCG load in the lungs than mice exposed only to BCG (p < 0.05). DEP treatment alone had no effect on the total number of lung lymphocytes or numbers of T, B, or NK cells recovered from lungs. In contrast, BCG infection significantly increased (p < 0.05) recovery levels of all types of lymphocytes from lungs. Coexposure to DEP + BCG further increased the recovery of lymphocytes from lungs of BCG-infected mice. The pulmonary lymphocyte subpopulation expressing the greatest levels of mRNA for IFNγ after BCG infection was CD4+ T cells. Expression levels were similar in mice exposed to BCG or BCG + DEP and were elevated as compared to noninfected mice and mice treated with DEP alone. Recovery of IFNγ-secreting lymphocytes and IFNγ-secreting T cells was significantly higher (p < 0.05) from lungs of BCG-infected mice as compared to control or DEP-exposed mice. BCG and BCG+DEP groups of mice did not differ significantly in the numbers of IFNγ-secreting lymphocytes in lungs. Taken together, these results indicated that coexposure to DEP+BCG did not significantly affect the level of IFNγ response of mice to BCG infection. However, DEP treatment was found to inhibit IFNγ-induced nitric oxide (NO) production by mouse alveolar macrophages in vitro. Our results indicate that DEP exposure did not alter the IFNγ response to BCG infection, but reduced responsiveness of alveolar macrophages to IFNγ . Reduced sensitivity of DEP-exposed alveolar macrophages to IFNγ may contribute to a greater load of BCG in the lungs of BCG-infected mice given DEP.