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. 1998 Mar;66(3):974-9.
doi: 10.1128/IAI.66.3.974-979.1998.

Immunoglobulins to group A streptococcal surface molecules decrease adherence to and invasion of human pharyngeal cells

Affiliations

Immunoglobulins to group A streptococcal surface molecules decrease adherence to and invasion of human pharyngeal cells

U Fluckiger et al. Infect Immun. 1998 Mar.

Abstract

The M protein is one of the most important virulence factors of group A streptococci (Streptococcus pyogenes) and may play an important role in the first steps of streptococcal infection. Since acute pharyngitis is a frequently occurring infectious disease caused by these bacteria, we wished to know whether antibodies to the M protein or other surface components inhibit adherence and internalization of streptococci to pharyngeal cells. We investigated the role of whole human secretory immunoglobulin A (sIgA), M6 protein-specific sIgA, and M6 protein-specific serum IgG in the inhibition of streptococcal adherence and internalization to cultured human pharyngeal cells. S. pyogenes D471, which produces a type 6 M protein (M+), and its isogenic M-negative (M-) derivative JRS75 were tested. Purified whole sIgA, M protein-specific sIgA, and sIgA preabsorbed with M protein were able to decrease significantly the adherence of streptococci to pharyngeal cells. Purified IgG against the M6 protein did not diminish the attachment of streptococci to the pharyngeal cells but did reduce internalization. Thus, our data suggest that secretory IgA may play a key role in preventing streptococcal infection at mucosal surfaces by blocking adherence while affinity-purified anti-M protein-specific IgG blocks epitopes responsible for invasion.

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Figures

FIG. 1
FIG. 1
Electron microscopy demonstrating the attachment and internalization of streptococci by human cultured pharyngeal cells. Bacteria were observed to associate with microvilli upon initial contact with the pharyngeal cells. Membrane extension is observed for the internalization process. Close observation indicates that surface proteins are involved with this initial interaction. Intracellular streptococci are found enclosed in cytoplasmic vacuoles with bacterial surface proteins still in contact with the membrane surface. The bacterial inoculum was prepared as described for the standard internalization assay. Magnification, ×12,700 (A) and 24,300 (B).
FIG. 2
FIG. 2
Effect of purified rabbit IgG and different preparations of human sIgAs on the adherence of group A streptococci to pharyngeal cells. The M+ strain (106 CFU) was incubated with purified rabbit IgG, purified sIgA, purified sIgA preabsorbed with M protein, or purified M protein-specific sIgA. All were at the final ELISA titer/well shown. Untreated M+ and M− strains were used as controls. Infected monolayers were incubated for 3 h, dispersed by addition of 0.25% trypsin–1 mM EDTA, and lysed with H2O. Error bars, SD; ∗, P < 0.05 compared to controls.
FIG. 3
FIG. 3
Adherence and internalization of M+ and M− strains in the presence of preimmune rabbit serum and hyperimmune rabbit serum raised against the M6 protein. Thirty minutes prior to the inoculation of the confluent monolayers, bacteria (5 × 105 CFU) were incubated at various dilutions of the preimmune rabbit serum or the hyperimmune rabbit serum in PBS supplemented with Mg2+ and Ca2+. The adherence was performed as described in the legend to Fig. 2. For the internalization assay, monolayers were infected for 3 h, treated with antibiotics for 2 to 3 h, dispersed by addition of 0.25% trypsin–1 mM EDTA, and lysed with H2O. Data represent the means ± SD (error bars) of two to three independent experiments with two infected wells per experiment.
FIG. 4
FIG. 4
Effect of purified M protein-specific IgG on the internalization process of M+ streptococci. Purified IgG at a protein concentration of 0.15 mg/ml was added to approximately 5 × 105 CFU and incubated at room temperature for 30 min and then added to the pharyngeal cells. The M+ and M− strains alone were used as controls. The internalization assay was performed as described in the legend to Fig. 3. Data represent the means ± SD (error bars) of two independent experiments with two infected wells per experiment. ∗∗, P < 0.01.

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