Immunogenicity and protective efficacy of GroEL (hsp60) of Streptococcus pneumoniae against lethal infection in mice

The present study was carried out to evaluate the immunogenicity and protective efficacy of GroEL (hsp60) of Streptococcus pneumoniae, by expressing full length GroEL in heterologous host Escherichia coli BL21 (DE3). PCR-amplified groEL. was ligated in pQE 30 expression vector and subsequently transformed in E. coli DH5 alpha strains. Cloning of groEL was confirmed by double digestion, followed by DNA sequencing. The His-tag containing recombinant GroEL was purified by Ni-NTA affinity chromatography. To determine the immunogenicity of GroEL, the mice were immunized by injecting 40 mu g GroEL protein per mouse intraperitoneally. The results showed a significant increase in antibody titre and lymphocyte proliferation in animals immunized with GroEL as compared with control. Further, there was an appreciable increase in interleukin-2 (IL-2) and IL-4 production in lymphocytes isolated from immunized mice as compared with control. To determine the efficacy of GroEL in eliciting protection, the mice were challenged with the lethal dose of S. pneumoniae A66 type 3 capsular strain intranasally after the seventh day of the last immunization. In the GroEL-immunized mice the onset of death was insignificantly delayed and all the mice died by the seventh day postinfection.