Western blot analysis of antibody response to pneumococcal protein antigens in a murine model of pneumonia.

To detect new antigen candidates for serological tests, we studied the antibody response to pneumococcal protein antigens in mice infected intratracheally with various Streptococcus pneumoniae strains. Sera were tested by Western blotting against whole-cell protein extracts. Mice developed a detectable immunoglobulin G-type response against a small number of polypeptides. The antibody response was strain dependent: sera from individuals infected with the same strain gave similar banding patterns on immunoblots. The banding patterns varied with the strain used for infection. However, a band at 36 to 38 kDa was recognized by all reactive sera. This band appeared to correspond to a polypeptide that was antigenically well conserved among the different S. pneumoniae serotypes. An antibody response to this antigen developed in mice irrespective of the capsular type, the virulence, and the susceptibility to penicillin G of the infecting strain. Thus, this 36- to 38-kDa protein antigen may be of value for the development of a serological test for humans.