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

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 region (PR) of PspA and tested it as a recombinant vaccine against infection caused by a clinical isolate (SP19) of Streptococcus pneumoniae serotype 19F. Our results showed that BALB/c mice immunized with recombinant proline-rich (rPR) region showed a significant higher antibody titre against rPR region compared to control non-immunized group. However, immunized mice or mice recived polyclonal antibodies against rPR region challenged via the intra-peritoneal route with a lethal dose of SP19 isolate showed no significant difference in survival compared to control non-immunized group. These results suggested that, immunization of BALB/c mice with rPR region of PspA is not protective against infection caused by serotype 19F in a mouse model.