Mice deficient in CD18, which lack all four CD11 integrins, have leukocytosis and increased susceptibility to bacterial infection. To determine the effect of deficiencies in LFA-1 (CD11a/CD18) or Mac-1 (CD11b/CD18) on host defense against systemic bacterial infection, knockout mice were inoculated i.p. with Streptococcus pneumoniae. Increased mortality occurred in both LFA-1−/− (15 of 17 vs 13 of 35 in wild type (WT), p < 0.01) and Mac-1−/− (17 of 34 vs 6 of 25, p < 0.01) mice. All deaths in LFA-1−/− mice occurred after 72 h, whereas most deaths in Mac-1−/− mice occurred within 24–48 h. At 24 h, 21 of 27 Mac-1−/− mice were bacteremic, vs 15 of 25 WT (p = 0.05); no difference was observed between LFA-1−/− and WT. Increased bacteria were recovered from Mac-1−/− spleens at 2 h (p = 0.03) and 6 h (p = 0.002) and from livers (p = 0.001) by 6 h. No difference was observed at 2 h in LFA-1−/− mice, but by 6 h increased bacteria were recovered from spleens (p = 0.008) and livers (p = 0.04). Baseline and peak leukocyte counts were similar between Mac-1−/− and WT, but elevated in LFA-1−/−. At 8 h, peritoneal neutrophils were increased in Mac-1−/−, but not significantly different in LFA-1−/−. Histopathologically, at 24 h Mac-1−/− animals had bacteremia and lymphoid depletion, consistent with sepsis. LFA-1−/− mice had increased incidence of otitis media and meningitis/encephalitis vs WT at 72 and 96 h. Both Mac-1 and LFA-1 play important but distinct roles in host defense to S. pneumoniae.

No abstract

When analyzed in a flow cytometer, particles are suddenly accelerated to high velocities (1–10 m.s−1) over very short distances. This feature is essential to obtain high analysis rates and low coincidence levels, but translates into very strong velocity gradients (> 105 s−1): particles experience strong hydrodynamic stresses that elongate them acid tend to dissociate weakly associated complexes. In order to analyze fragile conjugates formed by heterotypic adhesion between two cell types, a flow cytometer was modified to make hydrodynamic stress not only much weaker but also adjustable. A new and easily adaptable flow cell was designed for the instruments of the FACS™ series; it provided satisfactory hydrodynamic conditions on a wide continous range of flow rates. Accompanying electronic adaptations permitted standard analysis between 0.01 and 10 m.s−1. At 0.01 m.s−1, the velocity gradient roughly amounts to 50 s−1. Conjugates formed by the adhesion between human B and resting T lymphocytes, disrupted in conventional flow cytometers, could be detected and precisely quantified provided analysis velocity was kept below 0.1 m.s−1. We conclude that low velocity flow cytometry makes possible the quantification of weak intercellular adhesion phenomena, and is potentially useful for the future development of new biomechamical techniques and other applications.

No abstract