Combinatorial requirements for adhesion molecules in mediating neutrophil emigration during bacterial peritonitis in mice.

To investigate the requirements for adhesion molecules in neutrophil emigration during peritonitis, mice received intraperitoneal injections of Streptococcus pneumoniae while the functions of multiple adhesion molecules were blocked. Emigration after 4 h was compromised by antibodies against ICAM-1 or genetic deficiency of ICAM-1. Anti-CD11a/CD18 antibodies decreased emigration in ICAM-1 mutant mice, suggesting that ICAM-1 independent emigration requires CD11/CD18 complexes. In contrast, mice mutant in ICAM-1 plus E-selectin showed no defect in emigration, suggesting that E-selectin commits neutrophils to an ICAM-1-dependent pathway during streptococcal peritonitis. However, in mutant mice lacking the three endothelial adhesion molecules E-selectin, P-selectin, and ICAM-1, emigration after 4 h was significantly compromised. Thus, P-selectin is essential to ICAM-1- and E-selectin-independent acute peritoneal inflammation. After 24 h of peritonitis, there were no differences between WT and E-selectin/P-selectin/ICAM-1 mutant mice, demonstrating that these endothelial adhesion molecules are not essential to neutrophil emigration during later stages of peritonitis.

Neutrophil emigration in the skin, lungs, and peritoneum: different requirements for CD11/CD18 revealed by CD18-deficient mice.

To determine the role of CD11/CD18 complexes in neutrophil emigration, inflammation was induced in the skin, lungs, or peritoneum of mutant mice deficient in CD18 (CD18-/- mutants). Peripheral blood of CD18-/- mutants contained 11-fold more neutrophils than did blood of wild-type (WT) mice. During irritant dermatitis induced by topical application of croton oil, the number of emigrated neutrophils in histological sections of dermis was 98% less in CD18-/- mutants than in WT mice. During Streptococcus pneumoniae pneumonia, neutrophil emigration in CD18-/- mutants was not reduced. These data are consistent with expectations based on studies using blocking antibodies to inhibit CD11/CD18 complexes, and on observations of humans lacking CD11/CD18 complexes. The number of emigrated neutrophils in lung sections during Escherichia coli pneumonia, or in peritoneal lavage fluid after 4 h of S. pneumoniae peritonitis, was not reduced in CD18-/- mutants, but rather was greater than the WT values (240 +/- 30 and 220 +/- 30% WT, respectively). Also, there was no inhibition of neutrophil emigration during sterile peritonitis induced by intraperitoneal injection of thioglycollate (90 +/- 20% WT). These data contrast with expectations. Whereas CD11/CD18 complexes are essential to the dermal emigration of neutrophils during acute dermatitis, CD18-/- mutant mice demonstrate surprising alternative pathways for neutrophil emigration during pneumonia or peritonitis.

Neutrophil margination, sequestration, and emigration in the lungs of L-selectin-deficient mice.

These studies tested the hypothesis that L-selectin plays a role in neutrophil traffic in the lungs, particularly in neutrophil margination, sequestration, and emigration, using L-selectin-deficient mice. No defect in neutrophil margination within either capillaries or arterioles and venules was observed in uninflamed lungs of L-selectin-deficient mice. The initial rapid sequestration of neutrophils within the pulmonary capillaries 1 min after intravascular injection of complement fragments was not prevented. In contrast, L-selectin did contribute to the prolonged neutrophil sequestration (> or = 5 min). Interestingly, neutrophil accumulation within noncapillary microvessels required L-selectin at both 1 and 5 min after complement injection. During bacterial pneumonias, L-selectin played a role in neutrophil accumulation within noncapillary microvessels in response to either Escherichia coli or Streptococcus pneumoniae and within capillaries in response to E. coli but not S. pneumoniae. However, L-selectin was not required for emigration of neutrophils or edema in response to either organism. These studies demonstrate a role for L-selectin in the prolonged sequestration of neutrophils in response to intravascular complement fragments, in the intracapillary accumulation of neutrophils during E. coli-induced pneumonia, and in the accumulation of neutrophils within noncapillary microvessels when induced by either intravascular complement fragments or

Neutrophil emigration in the lungs.

Neutrophil emigration into the lung occurs in response to inflammatory mediators in the interstitium and the airspace. Emigration through the pulmonary microvasculature occurs through two pathways, one that requires CD11/CD18 and ICAM-1 and one that does not: Which pathway is utilized is determined by the stimulus. The ability of a stimulus to upregulate ICAM-1 by inducing the production of pro-inflammatory cytokines including TNF-alpha appears to determine the selection of the CD11/CD18, ICAM-1, ICAM-1-dependent pathway Recently, a third pathway has been identified that requires CD11/CD18 but not ICAM-1. The ligand for this pathway, as well as the ligands for CD11/CD18, ICAM-1-independent adhesion have not been identified. During recurrent pneumonia, the adhesion molecules required for emigration are different than those utilize during acute inflammation in previously normal lung tissue. For example, studies investigating the role of CD11/CD18 in recurrent pneumonia induced by P. aeruginosa, a stimulus which elicits CD11/CD18-dependent emigration initially, showed that when the organisms are instilled at the same site 7 days after the initial instillation, most emigration occurs through CD11/CD18-independent mechanisms. These studies suggest that when an acute stimulus is placed at a site of resolving inflammation, new pathways of adhesion are recruited. Whether these molecules are the same ones mediating acute CD11/CD18-independent adhesion remains to be determined. In summary, neutrophil emigration in the lung can occur through several adhesion pathways, which pathway is utilized can change during the inflammatory process, and cytokines participate in the selection of the pathway.

Selectins and neutrophil traffic: margination and Streptococcus pneumoniae-induced emigration in murine lungs.

The roles of selectins in the pulmonary margination and emigration of neutrophils were investigated by using mice genetically deficient in both E- and P-selectins (E/P mutants) and/or by intravenous injections of fucoidin (inhibiting both L- and P-selectins). E/P mutants were neutrophilic (14.7 +/- 4.9 x 10(6) vs. 0.8 +/- 0.1 x 10(6) neutrophils/ml). This neutrophilia was associated with increased margination of neutrophils within pulmonary capillaries (39.7 +/- 9.4 vs. 4.6 +/- 1.1 neutrophil profiles per 100 red blood cell profiles) but no change in margination within noncapillary pulmonary microvessels. After intratracheal instillation of Streptococcus pneumoniae, lungs of E/P mutants displayed increased neutrophil emigration (564 +/- 92 vs. 116 +/- 19 neutrophils per 100 alveolar profiles), edema (5.3 +/- 1.5 vs. 1.5 +/- 0.4 microliter/g body weight), and histologic evidence of lung injury compared with those in wild-type (WT). Fucoidin treatment did not affect neutrophil emigration during streptococcal pneumonia in WT or E/P mice. During pneumonia, the number of white blood cells (WBC) tethered to or spread upon the noncapillary vessel endothelium increased in both WT and E/P lungs. These are the first data demonstrating that neutrophil margination in uninfected pulmonary capillaries does not require E- and P-selectins; that streptococcal pneumonia induces an E- and P-selectin-independent increase in WBC interactions with noncapillary endothelium; and that migration of neutrophils to alveoli can occur despite deficiency or inhibition of all of the known selectins.

Effect of pentoxifylline on changes in neutrophil sequestration and emigration in the lungs.

The response of neutrophils to inflammatory stimuli includes sequestration, adhesion, and migration. Pentoxifylline protects against many neutrophil-mediated lung injuries. This study investigated whether pentoxifylline prevented changes in neutrophil kinetics induced by infusion of complement fragments or neutrophil emigration induced by Streptococcus pneumoniae. Complement fragments were infused in New Zealand White rabbits treated with pentoxifylline or saline, and the circulating neutrophil counts in the arterial and venous blood samples were measured. Neutrophil emigration was induced by intrabronchial instillation of S. pneumoniae and quantitated morphometrically. The results show that, at doses achievable in vivo, pentoxifylline did not prevent either the CD18-dependent or -independent phase of complement-mediated neutrophil sequestration within the pulmonary microvasculature or the release of neutrophils from the bone marrow. Pentoxifylline also did not alter either the deformability of unstimulated leukocytes or stimulus-induced decreases in deformability. Finally, neutrophil emigration into the alveolar space was neither attenuated nor accentuated by pentoxifylline. These data suggest that, in vivo, pentoxifylline does not protect against lung injury by inhibiting neutrophil sequestration or emigration and may act to alter the generation of mediators that affect neutrophil behavior, rather than acting directly on neutrophils.