Cytokine gene expression in the lungs of BALB/c mice during primary and secondary intranasal infection with Mycoplasma pneumoniae

Cytokine gene expression was determined in vivo in the lungs and spleens of Mycoplasma pneumoniae-infected BALB/c mice by means of qualitative and semiquantitative PCR-mediated mRNA amplification. During the acute phase of both primary and secondary infections, cytokines commonly associated with innate resistance, TNF alpha, IFN gamma, IL-1 beta and IL-6, were expressed. In contrast, early expression of the genes for IL-2 and IL-2 receptor was detected only during reinfection. Expression was greater in the lungs than in the spleen, attesting to the rapid accumulation of lymphocytes at the infected site. Interestingly, IL-2 mRNA expression declined rapidly and was no longer detectable after 24 h, whereas IL-10 mRNA levels rose sharply during the same period. During reinfection, mRNAs for TNF alpha and IL-6 were 10-fold and for IFN gamma about 50-fold higher than during primary challenge. The results suggest that the pathogenesis of M. pneumoniae diseases may be associated with elevated expression of proinflammatory cytokines.