Immunological and Pathological Aspects of Respiratory Tract Infection with Stenotrophomonas maltophilia in BALB/c Mice

A comprehensive study on the production of inflammatory mediators in the lungs of BALB/c mice following infection with Stenotrophomonas maltophilia was conducted. The levels of pro-inflammatory cytokines, tumor necrosis factor alpha (TNF-alpha) and Interleukin-1beta (IL-1 beta) was raised in the lungs of infected mice compared to control. The production of anti-inflammatory cytokine IL-10 was slightly delayed. Its peak level was on 2nd day whereas the peak of pro-inflammatory cytokines was observed on day one after intranasal challenge. This was accompanied with a rise in Myeloperoxidase (MPO) and Malondialdehyde (MDA) on day one. The increase in MPO levels matched with histopathological observations as neutrophils infiltration was detected on the first day. Alveolar macrophages (AMs) obtained from infected animals showed higher rate of uptake and killing when exposed to bacteria in vitro compared to similar experiment conducted with AMs from normal mice (control). This suggests that AMs were more efficient in cleaning the bacteria. The nitric oxide (NO) production though started early during infection but reached its maximum on 3rd day. No mortality was observed among the infected animals and infection was resolved by 5th post infection day. No drastic changes in the lung tissue were observed on histopathological examination.