Immune exclusion by naturally acquired secretory IgA against pneumococcal pilus-1
Ulrike Binsker, … , Alexandria J. Hammond, Jeffrey N. Weiser
Ulrike Binsker, … , Alexandria J. Hammond, Jeffrey N. Weiser
Published November 5, 2019
Citation Information: J Clin Invest. 2020;130(2):927-941. https://doi.org/10.1172/JCI132005.
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Research Article Microbiology

Immune exclusion by naturally acquired secretory IgA against pneumococcal pilus-1

Abstract

Successful infection by mucosal pathogens requires overcoming the mucus barrier. To better understand this key step, we performed a survey of the interactions between human respiratory mucus and the human pathogen Streptococcus pneumoniae. Pneumococcal adherence to adult human nasal fluid was seen only by isolates expressing pilus-1. Robust binding was independent of pilus-1 adhesive properties but required Fab-dependent recognition of RrgB, the pilus shaft protein, by naturally acquired secretory IgA (sIgA). Pilus-1 binding by specific sIgA led to bacterial agglutination, but adherence required interaction of agglutinated pneumococci and entrapment in mucus particles. To test the effect of these interactions in vivo, pneumococci were preincubated with human sIgA before intranasal challenge in a mouse model of colonization. sIgA treatment resulted in rapid immune exclusion of pilus-expressing pneumococci. Our findings predict that immune exclusion would select for nonpiliated isolates in individuals who acquired RrgB-specific sIgA from prior episodes of colonization with piliated strains. Accordingly, genomic data comparing isolates carried by mothers and their children showed that mothers are less likely to be colonized with pilus-expressing strains. Our study provides a specific example of immune exclusion involving naturally acquired antibody in the human host, a major factor driving pneumococcal adaptation.

Authors

Ulrike Binsker, John A. Lees, Alexandria J. Hammond, Jeffrey N. Weiser

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Figure 4

Pilus-1 component RrgB mediates pneumococcal adherence and binding to sIgA.

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Pilus-1 component RrgB mediates pneumococcal adherence and binding to sI...
(A) Adherence of WT Spn and isogenic mutants deficient for 1 or 2 pilus-1 components to hNF was assessed in a solid-phase assay. Each bacteria (2 × 104 per 100 μL DMEM) were incubated with 10 μg hNF in the presence of 0.1% BSA for 2 hours at 30°C. Bound bacteria were determined by resuspension with 0.001% Triton X-100 following plating on TS agar plates supplemented with 200 μg/mL streptomycin. n = 5–18. (B) Flow cytometric analysis of sIgA binding by WT Spn and isogenic mutants in soluble hNF. Bacteria (5 × 106 CFU per 50 μL) were incubated with 50 μg/mL of hNF. Binding of surface-associated sIgA was analyzed using a FITC-labeled goat anti-human IgA1 antibody and is shown as the percentage binding. n = 6. (A and B) Results of at least 3 independent experiments are illustrated as mean values ± SD. *P < 0.05, ****P < 0.0001 vs. TIGR4 by 1-way ANOVA followed by Dunnett’s multiple comparison. (C) Inhibition adherence assay using pilus-1–specific antisera. Bacteria were each pretreated with 5 μg/mL of rabbit control serum or anti-RrgA or anti-RrgB antiserum before incubation with immobilized hNF for 2 hours at 30°C. Detection of bound bacteria was analyzed as described in A. n = 6. Results of 3 independent experiments are illustrated as mean values ± SD. **P < 0.01, ****P < 0.0001 vs. without by 1-way ANOVA followed by Šidák’s multiple comparison.