Intranasal immunization with autolysin (LytA) in mice model induced protection against five prevalent Streptococcus pneumoniae serotypes in China.

In order to evaluate immunogenicity and protective efficacy of LytA from Streptococcus pneumoniae, we subcloned the full-length lytA-encoded autolysin (LytA) from 5 major pathogenic serotype isolates in China and obtained purified rLytA. Bioinformatics analysis showed that sequences of LytA were highly conserved in all strains we used in this work, and western blot analysis demonstrated that rLytAs from heterogeneous serotypes were cross-recognized by serum of mice infected with 23F strain SH137. Mice were intranasally immunized with purified rLytA, and serum anti-rLytA IgG, IgA and secretory IgA were elicited. More importantly, rLytA intranasal-immunized mice showed a significantly higher survival rate and lower bacterial carriage in response to infection by Streptococcus pneumoniae. The fact that mice immunized with rLytA from strain SH137 also had a higher survival rate after intraperitoneal injection of other four serotype strains of living S. pneumoniae suggested that it possessed cross-protection effect. Our study revealed that intranasal immunization with rLytA may protect mice against mucosal and systemic pneumococcal infection; hence, it was an attractive vaccine candidate.