Nuclear factor-kappaB activation in mouse lung lavage cells in response to Streptococcus pneumoniae pulmonary infection.

OBJECTIVES

To assess the state and activation kinetics of the nuclear transcription regulatory protein nuclear factor-kappB (NF-kappaB) in lung lavage cells in a murine pneumococcal pneumonia model and to determine how the virulence of the infecting organisms altered the activation state of NF-kappaB.

DESIGN

Experimental, comparative study of three Streptococcus pneumoniae strains that induced three distinct pulmonary diseases.

SETTING

Experimental laboratory in a university-based medical center.

SUBJECTS

Female BALB/cby mice, 8-10 wks of age.

INTERVENTIONS

We randomly divided the mice into the following five groups: a) the control group; b) animals infected by virulent encapsulated S. pneumoniae P4241 strain; c) animals infected by avirulent encapsulated S. pneumoniae P15986 strain; d) animals infected by avirulent unencapsulated S. pneumoniae R6 strain; e) animals infected by virulent lysed S. pneumoniae P4241 strain. Animals were anesthetized and infected by intratracheal delivery of 4 x 10(5) colony-forming units (CFU) of S. pneumoniae per mouse or bacterial components equivalent to 4 x 10(5) CFU for lysed S. pneumoniae challenge. After intratracheal challenge with virulent encapsulated strain P4241, mice developed acute pneumonia, became bacteremic, and died within 3 to 5 days. None of the mice infected with the avirulent encapsulated strain P15986 or the avirulent unencapsulated strain R6 died. After collection of lung lavage cells and nuclear extraction, NF-kappaB activation was determined 1 hr, 4 hrs, 6 hrs and 24 hrs after pneumococcal infection. At the same time, pulmonary and blood clearance, bronchoalveolar lavage cells population, and tumor necrosis factor-alpha production were assessed (six mice per time point).

MEASUREMENTS AND MAIN RESULTS

NF-kappaB was constitutively expressed within nuclear extracts of lung lavage cells from uninfected control mice. A significant increase in NF-kappaB activation was detected within 1 hr after injection of virulent lysed S. pneumoniae P4241 strain (bacterial components equivalent to 4 x 10(5) CFU), and was still present 24 hrs after the injection. After live pneumococcal challenge, significant NF-kappaB activation was detected within 4 hrs with a peak at 24 hrs. Responses to all three strains (P4241, P15986 and R6) were time-dependent (p < .0001), as NF-kappaB activation gradually increased during the first 24 hrs. Moreover, compared with the control uninfected mice, the intensity of the retarded KB oligonucleotide, as determined by densitometry, was increased approximately four- to five-fold and seven-fold in reactions containing nuclear extracts isolated 24 hrs after infection with the avirulent strains P15986 or R6 and the virulent strain P4241, respectively. With the virulent strain P4241, responses were significantly stronger than with the avirulent strains P15986 and R6 (p < .01). Responses were of similar order with avirulent strains P15986 and R6 (p > .05).

CONCLUSION

Pulmonary infection by S. pneumoniae induced delayed and time-dependent activation of NF-kappaB in mouse lung lavage cells. The degree of NF-kappaB activation in lung lavage cells correlated with the virulence of the infecting organisms. Our results suggest that the more severe the infection, the higher the rise in NF-kappaB.