Faculty Bibliography

Aggregation of bacteria by zinc and lysozyme was studied and compared with aggregation induced by a high-molecular-weight salivary agglutinin. Each ligand was found to exhibit a unique profile of properties when examined by both a microradiochemical centrifugation assay and a turbidimetric assay. Significant differences in rate of aggregation and bacterial species specificity were noted. Zinc- and lysozyme-mediated aggregations were shown to be calcium independent and to proceed rapidly at 0 degree C, in contrast to the salivary agglutinin. Zinc produced large, asymmetric aggregates, saliva produced intermediate-sized aggregates, and lysozyme produced the smallest aggregates. These size differences are consistent with many of the observed reaction properties.

We have investigated the use of an isoelectric focusing (IEF) technique for isolating and characterizing matrix vesicles. Focusing was performed on crude preparations of matrix vesicles isolated from collagenase digests of chick epiphyseal cartilage and purified by discontinuous sucrose gradient centrifugation. Crude and partially purified vesicle preparations were subjected to flat bed IEF in a slurry of Pevikon-Sephadex. Partially purified matrix vesicles focused as a narrow band (pI congruent to to 6.5). Alkaline phosphatase, solubilized from matrix vesicles, focused with a pl of 4.0-4.5. The IEF profile of matrix vesicles also differed from that of chondrocyte membranes. Thus, the membrane pls were congruent to to 5.4 and 6.6-7.8, respectively. The latter peak probably corresponded to the pl of the matrix vesicle preparation. This observation lends support to the view that vesicles originate from distinct regions of the chondrocyte membrane.

Various cationic polyelectrolytes (poly-alpha-amino acids and histones), lectins, the chemotactic peptide, f-methionyl-leucyl-phenylalanine (fMLP), the calcium ionophore A23187, and phorbol myristate acetate (PMA) were investigated regarding their capacity to induce luminol-dependent chemiluminescence (LDCL) and superoxide production by human blood leukocytes. Although when tested individually, poly-L-arginine (PARG), phytohemagglutinin (PHA), concanavalin A (Con A), or fMLP induced only a low to moderate LDCL response, very intense synergistic CL reactions were obtained by mixtures of PARG + PHA, PARG + Con A, PARG + PHA + fMLP, Ca2 + ionophore + PARG + PHA + fMLP, and PARG + PMA. The sequence of addition of the various agents to WBC in the presence of luminol absolutely determined the intensity of the LDCL signals obtained, the highest reactions being achieved when the WBC were preincubated for 2-3 min with A23187 followed by the sequential addition of fMLP, PARG, and PHA. These "multiple hits" induced CL reactions which were many times higher than those obtained by each factor alone. On the other hand, neither poly-L-lysine, poly-L-ornithine, poly-L-histidine, nor poly-L-asparagine, when employed at equimolar concentrations, cooperated efficiently with PHA and fMLP to trigger synergistic LDCL responses in leukocytes. Concomitantly with the induction of LDCL, certain ligand mixtures also triggered the production of superoxide. The LDCL which was induced by the "cocktail" of agents was markedly inhibited by sodium azide (93% inhibition), but to a lesser extent by catalase (10% inhibition) or by superoxide dismutase (20%-60% inhibition). On the other hand, scavengers of singlet oxygen and OH (sodium benzoate, histidine) did not affect the synergistic LDCL responses induced by these multiple ligands. Cytochalasin B also markedly inhibited the LDCL responses induced either by soluble stimuli or by streptococci preopsonized either with histone or with polyanethole sulfonate. The LDCL responses which were induced by mixtures of PARG and concanavalin A were also strongly inhibited by mannose, alpha-methyl mannoside, and poly-L-glutamic acid. The data suggest that the LDCL responses induced by the soluble ligands involved a myeloperoxidase-catalyzed reaction. The possible employment of "cocktails" of ligands to enhance the bactericidal effects of PMNs, macrophages, and natural killer cells on microbial cells and mammalian targets is discussed.

A leukotoxin from Actinobacillus actinomycetemcomitans was isolated by a procedure that includes polymyxin B extraction, ion-exchange chromatography, and gel filtration chromatography. The procedure resulted in the recovery of 48% of the toxin with a 99-fold increase in specific activity. The isolated toxin has a molecular mass of 180,000 daltons by gel filtration and 115,000 daltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It retains all the major biological characteristics previously documented for crude leukotoxin preparations, including susceptibility to heat and proteolytic enzymes and neutralization by sera from patients with juvenile periodontitis. The isolated leukotoxin destroys human but not rat or guinea pig polymorphonuclear leukocytes and has no apparent effect on human erythrocytes. The availability of the A. actinomycetemcomitans leukotoxin should facilitate studies on its chemistry and mode of action as well as its role in the pathogenesis of human periodontal disease.

Human and animal sera contain potent inhibitors of saliva-mediated aggregation of oral streptococci. The inhibitors consist of a high-molecular-weight heat-labile factor and a lower-molecular-weight heat-activated factor. The latter appears to be serum albumin. Analyses of purified blood-derived proteins indicated that several high-molecular-weight proteins (fibrinogen, fibronectin, and ferritin) were able to inhibit aggregation at low concentrations. These data suggest that high-molecular-weight proteins may modulate the aggregation process.

Human parotid saliva contains agglutinins which bind to the surface of streptococci and induce the formation of bacterial aggregates. Bacterial aggregation can be blocked by proteins released from viable PMNs and platelets or by sonic extracts prepared from these cells. PMN and platelet inhibitors display characteristic differences in molecular weight, protease, and temperature sensitivity. The mechanism of action of the inhibitors appears to involve a direct interaction with the salivary agglutinins rather than with the bacteria. It is thus possible that PMN and platelet-derived products might modulate saliva-mediated bacterial aggregation and thereby influence the course of infections in the oral cavity.