Streptomyces spores from mouldy houses induce nitric oxide, TNFα and IL-6 secretion from RAW264.7 macrophage cell line without causing subsequent cell death.

The current view is that only bacterial lipopolysaccharide (LPS) and gamma interferon (IFNγ) are able to alone activate macrophages to secrete nitric oxide (NO), probably a causative agent of cell death. Moreover, some cytokines and gram positive pathogens together with IFNγ induce NO-production. Surprisingly, spores of Streptomyces sp., which are mesophilic gram-positive bacteria found in mouldy houses, stimulated RAW264.7 macrophages to produce pro-inflammatory cytokines, tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6), and induced the expression of inducible NO-synthase (iNOS) with a subsequent NO-production. However, the Streptomyces spores did not kill NO-producing macrophages, as did both LPS and gram negative bacteria Pseudomonas fluorescens, strong inducers of cytokine- and NO-production. These results imply that Streptomyces sp., induced cytokine and NO-secretion, may play a role in the responses evoked by exposure to these microbes. Moreover, factors other than, or in addition to NO, are necessary for cytotoxicity in murine macrophages.