Immunogenicity and protective efficacy of DnaJ (hsp40) of Streptococcus pneumoniae against lethal infection in mice

The present study was carried out to evaluate the immunogenicity and protective efficacy of DnaJ (hsp40) of Streptococcus pneumoniae, by cloning the full-length DnaJ of S. pneumoniae and expressing in heterologous host E. coli BL-21 (DE3). PCR amplified DnaJ was ligated in pQE-30 expression vector and subsequently transformed in E. coli DH5α strain. Cloning of DnaJ was confirmed by double digestion and PCR, followed by DNA sequencing. The His-tag containing recombinant protein was purified by Ni–NTA affinity chromatography. To determine the immunogenicity of DnaJ, the mice (10 mice/group) were immunized by injecting 40 μg DnaJ protein/mouse i.p. There was a significant increase in IgG titres (2 × 105) in mice immunized with DnaJ protein. Isotyping studies revealed that antibodies produced are predominantly IgG2a type indicating the predominance of Th1 response. A significant increase in lymphocyte proliferation was observed in mice immunized with DnaJ protein as compared to the control mice. Further, there was a significant increase in IL-2 and γ-IFN levels in culture supernatants of splenocytes isolated from immunized mice. To determine the efficacy of DnaJ vaccination in eliciting protection, the mice were challenged with 1 × 105 cells of S. pneumoniae A66 type 3 capsular strain intra-nasally after 7 days of last immunization. All the control mice died within 2 days of post-infection, while 70% of animals immunized with DnaJ survived the lethal challenge by S. pneumoniae. The study reveals that immunization of mice with DnaJ elicits protective immunity against S. pneumoniae infection.