Abstract
Here we show that mouse IgG2a and IgG1 antibodies specific for the commensal Streptococcus mitis cross-react with pathogen Streptococcus pneumoniae serotypes 2 and 4, although the cross-reactivity conferred by IgG2a is stronger than that by IgG1 antibodies. These findings may be important for understanding the S. mitis-induced IgG isotype responses and have consequences for the development of an effective pneumococcal vaccine.
Highlights
Streptococcus pneumoniae, a gram-positive bacterium that resides in the human upper respiratory tract, causes several diseases worldwide, such as pneumonia, sepsis, meningitis, and otitis media [1]
Our Western blotting showed that serum IgG2a and IgG1 antibodies from the S. mitis-immunized mice cross-reacted with multiple proteins of S. pneumoniae D39 and TIGR4
The S. mitis-immunized mice displayed significantly higher levels of IgG2 antibodies reactive to S. mitis and S. pneumoniae D39 and TIGR4 than IgG1 antibodies (Figure 1(b)). These findings reveal that following mucosal immunization with S. mitis, mice generate enhanced IgG2a and IgG1 antibody responses that cross-react with S. pneumoniae serotypes, the IgG2a responses are stronger than IgG1 responses
Summary
Streptococcus pneumoniae, a gram-positive bacterium that resides in the human upper respiratory tract, causes several diseases worldwide, such as pneumonia, sepsis, meningitis, and otitis media [1]. Current pneumococcal vaccines are effective against only those S. pneumoniae serotypes that are included in vaccines [2]. This underscores the exploration of alternative prophylactic strategies that provide protection against all serotypes. Streptococcus mitis, a commensal that is abundantly present in the oral cavity and shares phylogenetic, antigenic, and ecological characteristics with S. pneumoniae, has appeared as an interesting vaccine candidate that holds the potential to confer optimal immunity to pneumococcal infections [3, 4]. Recent studies have indicated a crucial role for IgG antibodies in defense against pneumococcal infections, it is unclear as to how S. mitis stimulates the host’s immune system to generate humoral responses [5]. Emerging evidence reveals that rabbits immunized with S. mitis generate IgG antibodies that are reactive with both S. mitis and S
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