Immunization with proline rich region of pneumococcal surface protein A has no role in protection against Streptococcus pneumoniae serotype 19F

Abstract Pneumococcal surface protein A (PspA) is one of the major virulence factors expressed by almost all pneumococcal serotypes and was suggested to be a promising universal vaccine candidate for all pneumococcal sero-groups. Here, we expressed and purified the proline-rich (PR) region of PspA and test it as a vaccine candidate against infection caused by a clinical isolate of Streptococcus pneumoniae of serotype 19F (SP19). Our results showed that BALB/c mice immunized with recombinant proline-rich (rPR) region showed a significant higher antibody titer against rPR region compared to control non-immunized group. However, immunized mice challenged intra-peritoneal route with a lethal dose of SP19 isolate showed no significant difference in survival compared to control non-immunized group. In addition, passive immunization of mice with rabbit polyclonal antibodies against rPR region showed no significant difference in survival time after S. pneumoniae infection. These results suggested that, immunization of BALB/c mice with rPR region of PspA is not protective against SP19 intra peritoneal infection in murine model.