Pneumococcal IgA1 protease subverts specific protection by human IgA1.

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Bacterial immunoglobulin A1 (IgA1) proteases are virulence factors that may interfere with host defense mechanisms.
• Immunoglobulin A (IgA) is crucial for mucosal immunity, but its effectiveness can be compromised by bacterial proteases.

Purpose of the Study:

• To investigate the in vitro and in vivo impact of bacterial IgA1 proteases on the protective functions of human IgA1 and IgA2 against Streptococcus pneumoniae.
• To determine if IgA1 protease activity can be neutralized by host immune components like IgG.

Main Methods:

• In vitro assays using IgA1 and IgA2 human monoclonal antibodies (hMAbs) challenged with IgA1 protease and Streptococcus pneumoniae.
• In vivo mouse infection models using wild-type and IgA1 protease-deficient S. pneumoniae strains.
• Analysis of complement-mediated bacterial reduction and neutrophil activity in mouse sera.
• Assessment of serum IgG's ability to inhibit IgA1 protease activity in patients with pneumococcal bacteremia.

Main Results:

• IgA1 proteases inhibited phagocytic killing of S. pneumoniae by IgA1 hMAbs in vitro by cleaving the Fcα1 heavy chain, but not IgA2.
• In vivo, IgA2 conferred better survival than IgA1 against S. pneumoniae, especially in the presence of IgA1 protease.
• Human serum IgG demonstrated inhibitory activity against IgA1 protease in a significant proportion of patients post-infection.

Conclusions:

• Bacterial IgA1 protease circumvents the protective effects of human IgA1 against S. pneumoniae in vivo.
• IgA1 protease is a significant factor in S. pneumoniae colonization and infection, suggesting its potential as a vaccine target.
• The development of neutralizing IgG antibodies against IgA1 protease is a key outcome of natural infection.