Intrapulmonary neutrophil apoptosis in a pig model of pneumonia.
BACKGROUND
Apoptosis and necrosis are two distinct cell death modalities. Polymorphonuclear leukocytes (PMNL) play an important role in pneumonia and little information is available on whether these cells are cleared by necrosis or apoptosis. We therefore compared the proportion of apoptotic PMNL in lung tissues with and without pneumonia. In addition, the association of PMNL apoptosis and mechanical ventilation (MV) was investigated.


METHODS
Samples obtained from a pig model developed to tracheobronchial stenting were analysed. Pneumonia was induced with that model in 10 animals (white-Landrace piglets, Pittman-Moore or Göttingen minipigs). Animals were sacrificed when clinical parameters of pneumonia became evident and 17 lung samples could be analysed for histologic evidence of pneumonia, growth of micro-organisms, and the apoptotic index (proportion of apoptotic PMNL over all PMNL in a 400-power field). In addition, lung samples (n = 7) from two pigs without stent implantation on mechanically ventilated for more than 48 h were studied.


RESULTS
A total of 9/17 samples (53%) showed histologic evidence of pneumonia, 11/17 (65%) had significant bacterial growth (> 10(3) cfu/g), and 7/17 (41%) fulfilled both criteria. The apoptotic index was not significantly different in samples with and without histologic evidence of pneumonia (pneumonia: 25.3 +/- 6.1% vs. No pneumonia: 25.2 +/- 11.9%; 95%CI: -9.7 - 9.5, p = 0.989) or in samples with and without significant bacterial growth (significant bacterial growth: 23.5+/-9.3% vs. No significant bacterial growth: 28.5+/-8.2%; 95%CI: -4.6 - 16.7; p = 0.284). However, the apoptotic index was higher in samples of pigs, mechanically ventilated for more than 48 h, compared to the stent group (MV: 36.9+/-10.7% vs. Stent: 25.2 +/- 9.0%; 95% CI: -20.5 - -2.9; p = 0.012).


CONCLUSIONS
In an animal model, the proportion of apoptotic PMNL was not different in lung samples with and without histologic or bacterial pneumonia. However, MV for more than 48 h was associated with a higher proportion of apoptotic PMNL in lung tissue. This study may be helpful for the understanding of the evolution of lung tissue damage induced by bacterial pneumonia and MV.
Bauer
T T
TT
Abt. für Pneumologie, Allergologie und Schlafmedizin, Bergmannsheil, Klinikum der Ruhr-Universität, Bochum, Germany.
Arce
Y
Y
Marquette
C-H
CH
Ramirez
J
J
El-Ebiary
M
M
Ewig
S
S
Horowitz
S
S
Torres
A
A
D000818:Animals; D017209:Apoptosis; D004195:Disease Models, Animal; D004926:Escherichia coli; D020287:In Situ Nick-End Labeling; D007711:Klebsiella pneumoniae; D008168:Lung / Q000382:microbiology / Q000473:pathology*; D009504:Neutrophils / Q000473:pathology*; D018410:Pneumonia, Bacterial / Q000473:pathology*; D012121:Respiration, Artificial / Q000009:adverse effects; D013211:Staphylococcus aureus; D013291:Streptococcus; D013552:Swine