Characterization and cross-reactivity of rabbit antisera to plaque toxins

Identification of lysine decarboxylase as a mammalian cell growth inhibitor in Eikenella corrodens: possible role in periodontal disease

The pathogenesis of inflammatory periodontal disease was studied by examining the mechanism of HeLa and HL60 cell growth inhibition by cell-free saline-soluble extracts of Eikenella corrodens and bacterial plaque. Previous studies identified a protein (p80) as causing growth inhibition by E. corrodens extracts. After purification by two-dimensional SDS-PAGE, p80 was digested with protease lysC. Amino acid sequences were obtained and backtranslated for use as PCR primers. A 5840 nucleotide sequence containing a lysine decarboxylase gene was obtained from a Sau3 A1 genomic library of E. corrodens DNA. Lysine decarboxylase activity was present at physiologic pH in the E. corrodens extracts containing p80, and also in bacterial plaque. Both extracts caused growth inhibition by depleting lysine from cell culture media through conversion to cadaverine. Adding lysine, or immune goat IgG to a peptide derived from the active site sequence of E. corrodens lysine decarboxylase, retarded lysine depletion and growth inhibition. epsilon-Amino caproic acid specifically enhanced lysine decarboxylase activity at the low lysine concentration in HL60 cell culture media, and also increased the growth inhibition. Thus, lysine decarboxylases such as p80 inhibit growth by removing lysine from mammalian cell culture media. A new role for lysine decarboxylase activity in the microbial aetiology of periodontal disease is discussed.

An Eikenella corrodens toxin detected by plaque toxin-neutralizing monoclonal antibodies

Bacterial plaque from the gingival region of teeth contains cytotoxic agents which lyse undifferentiated human HL60 cells. A small panel of monoclonal antibodies (MAbs) was found to abrogate much of this activity and to detect antigens in certain strains of Streptococcus mitis and Eikenella corrodens. The aim of this study was to determine whether these bacterial antigens might be involved in HL60 cells cytolysis. Saline extracts were obtained by homogenizing washed, stationary-phase cells in 65 mM NaCl with a tight-fitting Potter-Elvehjem homogenizer. The extracts of E. corrodens were toxic to HL60 cells, whereas similar extracts of S. mitis were nontoxic. Adding plaque toxin-neutralizing MAb 3hE5 blocked the toxic effect of E. corrodens extract S. mitis extracts contained a single, strongly reactive antigen of 140 kDa (s140K antigen) detected on Western blots (immunoblots) by three MAbs from the panel. Rabbit antibodies raised to this antigen excised from the gel (anti-s140K serum) detected larger antigens in addition to s140K. E. corrodens extracts contained a number of antigens detected by the MAbs. Immunoglobulin G (IgG) was purified from anti-s140K serum by passage through DE52 cellulose. A 100-fold excess (by weight) of the purified IgG to E. corrodens protein specifically cross-precipitated an 80-kDa antigen plus a nonantigenic 16-kDa protein, presumably attached noncovalently. The remaining supernatant fraction had no toxic activity. A similar ratio of control IgG (from nonimmunized rabbits) did not precipitate these proteins, and the supernatant fraction had the same activity as the extract not treated with IgG. The proteins of 80 and 16 kDa were also detected in the anti-s140K immunoprecipitate by rabbit IgG antibodies to E. corrodens whole cells. The 80-kDa antigen, alone or complexed with the 16-kDa protein, may be involved in mediating the toxic activity in E. corrodens and plaque extracts.

Bacteria reactive to plaque-toxin-neutralizing monoclonal antibodies are related to the severity of gingivitis at the sampled site

Certain monoclonal antibodies (Mabs) neutralize the inhibition of HL60 cell growth by bacterial plaque extracts. The aim of this study was to enumerate and identify the bacteria reactive to these Mabs at sites where periodontal disease was measured by gingival index, pocket depth and attachment loss. The bacterial colonies were grown on blood agar and the colonies counted directly and after immunoblotting. Sites that bled on probing (n = 15) had a mean of 3.35% Mab-positive colonies (SEM = 0.52%) and sites that did not bleed (n = 9) had a mean of 1.61% (SEM = 0.41%). The percentage of Mab-positive colonies also correlated with gingival index but not with the total number of colonies sampled, attachment loss or pocket depth. Antigen was expressed by 4 genera: strains of Streptococcus sanguis and/or Eikenella corrodens (8 sites), Staphylococcus epidermidis (4 sites) and Corynebacterium minutissimus (1 site). The results suggest that the antigens detected on these bacteria by the Mabs may be processed to form toxins and maintain gingivitis by irritating the surrounding cells.

Use of monoclonal antibodies with neutralizing effects on toxic antigens from human bacterial plaque to detect specific bacteria by colony blotting

Inflammatory periodontal diseases are provoked by bacteria which adhere to teeth at the gingival margin and form plaques containing toxins detectable by their effect on mammalian cells in culture. The aim of this study was to make toxin-neutralizing monoclonal antibodies and determine whether they detect antigen in specific oral bacteria. Bacterial plaque was collected from teeth and homogenized, and the fluid phase (plaque extract) was boiled or first fractionated over Sephacryl S-300. Hybridomas from immunized mice secreted immunoglobulin M (IgM) antibodies which reacted to plaque antigens. Neutralization was detected by an increase in the growth of HL60 cells which were exposed to plaque toxins in the presence of IgM from hybridoma culture or ascitic fluids. However, the neutralization was obvious only when the plaque toxins reduced growth by 50% or less. Plaque toxin preparations were found to contain proteases which hydrolyzed all of the IgM in ascitic fluids within 24 h. Replenishing the IgM daily preserved protection compared with protection from IgM from other hybridomas or saline only. The decrease in the specific activity of plaque proteins caused by replenishing one such antibody (3hE5) was 2.5-fold compared with activity with unreplenished 3hE5, 3.8-fold compared with activity with saline only, and 10.7-fold compared with activity with replenished, unrelated antibody. The neutralizing IgM detected an array of 14,000- to 22,000-molecular-weight antigens. The native toxins may be aggregates of these antigens, or the array may indicate fragments of an undetected, larger antigen or a common, nonpeptide adduct. Only 0.5 to 0.8% of the bacteria from sites with periodontitis and grown on blood agar contained antigen. One group of reactive bacteria was identified as Actinomyces odontolyticus serotype I. Other isolates were identified as Staphylococcus epidermidis, but antigen disappeared from the these isolates within 6 weeks of subculture. Epitope-containing antigens were also found in streptococcal and Eikenella isolates, and it is likely that the antigens from only some of these bacteria are toxic.

Effect of Actinobacillus actinomycetemcomitans, Wolinella recta and Bacteroides gingivalis on the viability of retinoic acid-induced and dimethyl sulfoxide-induced HL-60 cells

We studied the interactions between viable and heat-killed, opsonized and unopsonized periodontopathic bacteria with both uninduced and induced HL-60 promyelocytic leukemia cells. The cells were induced to differentiate into granulocyte-like cells by incubation with retinoic acid (RA) or dimethyl sulfoxide (DMSO). When unopsonized, Wolinella recta ATCC 33228 significantly suppressed the net proliferation of uninduced HL-60 cells, Actinobacillus actinomycetemcomitans strain Y4 was markedly lethal to the cells, and Bacteroides gingivalis ATCC 33277 had no effect. Unopsonized and opsonized A. actinomycetemcomitans and W. recta had equally potent lethal effects on induced HL-60 cells. Unopsonized B. gingivalis was not lethal to the induced cells in the dose used (100 bacteria/HL-60 cell), but opsonized B. gingivalis was lethal, especially in the first 24 h. The killing effects of A. actinomycetemcomitans and W. recta were largely eliminated if they were heated (56 degrees C, 30 min) before being added to the induced HL-60 cells. RA-induced HL-60 cells were more sensitive to the lethal effects of A. actinomycetemcomitans and W. recta than were DMSO-induced cells. The results suggest that the HL-60 cell line may be a useful model for studying granulocyte-bacteria interactions.