Anti-pneumolysin activity of commercially available alpha 1-antitrypsin is due to cholesterol impurities.

Pneumolysin (PLY), the principal cytolytic toxin of Streptococcus pneumoniae, may be important in the pathogenesis of acute lung injury during pneumococcal pneumonia. However, the local host defenses that limit PLY injury to lung tissues have not been characterized. We investigated the ability of a commercial preparation of alpha 1-antitrypsin (alpha 1-AT), a major plasma anti-proteinase, to inhibit PLY. At normal plasma concentrations, the alpha 1-AT preparation prevented PLY injury to bovine pulmonary artery endothelial cells, rat alveolar epithelial cells, and human erythrocytes. The alpha 1-AT preparation selectively inhibited thiol-activated bacterial toxins; it was inactive against snake venom hemolysins, mastoparan, and oxygen-stable bacterial toxins. Biochemical characterization of the alpha 1-AT preparation and comparison with other available alpha 1-AT preparations revealed that this inhibitory activity was due to contamination with nanomolar concentrations of cholesterol. Characterization of non-immune human plasma anti-pneumolysin activity showed that beta-lipoprotein fractions contain the major inhibitory activity. We caution other investigators that the inhibition of bacterial virulence by these alpha 1-AT preparations may indicate toxin-mediated, rather than protease-mediated, mechanisms.

Peritoneal macrophages and opsonins: antibacterial defense in patients undergoing chronic peritoneal dialysis.

The antibacterial activity of phagocytic cells and opsonins in peritoneal dialysis effluents from 21 patients undergoing chronic peritoneal dialysis (CPD) was studied. Effluents contained an average of 12 x 10(6) cells per liter that were predominantly macrophages. Macrophages phagocytized and killed opsonized Staphylococcus epidermidis, Staphylococcus aureus, and Escherichia coli as efficiently as did polymorphonuclear neutrophils (PMNs) from healthy donors. Macrophage chemiluminescence was one-third of that observed with donor PMNs. In the absence of opsonins, macrophages efficiently phagocytized and killed S. aureus by binding S. aureus cell wall protein A to macrophage surface IgG. Nine (43%) of 21 effluents failed to opsonize S. epidermidis, and none opsonized E. coli. When present, titers of S. epidermidis opsonins were 50- to 100-fold lower than that of normal serum. IgG and C3 concentrations in effluent reflected its opsonic capacity. Macrophages from patients undergoing CPD thus have intact phagocytic and bactericidal functions. However, the low level of opsonic molecules and inadequate numbers of macrophages in the peritoneal cavity may predispose patients undergoing CPD to peritonitis.

Influence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin on Staphylococcus aureus growth in human phagocytic cells.

After an initial 2-h incubation with phagocytic cells, the growth of surviving intracellular Staphylococcus aureus was examined in the presence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin. One-tenth of the minimal inhibitory concentrations of these antibiotics markedly reduced bacterial growth in normal polymorphonuclear leukocytes. In contrast, when human alveolar macrophages were studied, no inhibition of growth was seen. Subinhibitory concentrations of these antibiotics and polymorphonuclear leukocytes acted synergistically to reduce intracellular survival of S. aureus. This synergy did not appear to be dependent upon the microbicidal potential of the leukocyte respiratory burst, since no differences were found when polymorphonuclear leukocytes obtained from patients with chronic granulomatous disease were compared with those from normal donors.