Cytokine mRNA expression in pneumococcal carriage, pneumonia, and sepsis in young mice.

We studied cytokine mRNA expression in Streptococcus pneumoniae carriage, pneumonia, and sepsis in 3-week-old, inbred C57BL/6 and BALB/c mice. Mice were inoculated intranasally with S. pneumoniae serotype 6B, 14, or 3. Survival, bacterial load in the nasopharynx (NP) and lungs, and mRNA levels of tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, interleukin (IL)-10, and IL-12 in the spleen were analyzed. No baseline mRNA expression levels were found, except for TNF-alpha in C57BL/6 mice. Serotype 6B caused NP colonization only, a significant (P<.05) increase in the levels of TNF-alpha, and induction of TGF-beta and IL-12 mRNA. Serotype 14 caused NP and nonlethal lung colonization and induction of TGF-beta, IL-10, and IL-12. Serotype 3 caused NP colonization, pneumonia, 35% mortality, and no alteration in the mRNA expression of tested cytokines. Although activation of the immune system culminated in nonlethal disease, evasion of the immune system was associated with detrimental disease.