Immunoblotting is of no value in the serodiagnosis of Streptococcus pneumoniae pneumonia

We studied five patients with bacteremic pneumococcal pneumonia to determine if Western blot analysis of the immune response to protein antigens of this microorganism could be used as a diagnostic tool on serum samples from patients with pneumonia of unknown etiology. The immune response to capsular polysaccharide (CP) was determined by Dr. G. Schiffman. All five patients had an increase in antibody to the infecting capsular polysaccharide type between the acute and convalescent serum samples. Depending on the antibody (polyvalent, IgM, IgA, IgG) and the sample tested (acute or convalescent), a number of protein antigens were recognized: polyvalent conjugate, 14–25 antigens with acute phase serum samples and 18–27 antigens with convalescent serum samples; IgM, 8–9 antigens with acute phase serum samples and 10–14 with convalescent phase serum samples; IgA, 2–11 antigens with acute phase serum samples and 10–12 protein antigen with convalescent phase samples; IgG, 6–14 antigen with acute phase and 17–19 antigens with convalescent phase serum samples. Antibodies were directed towards proteins with molecular weights ranging from 14,300 – 200,000 Da. There were no unique antibodies detected in the convalescent serum samples. We conclude that Western immunoblotting is of no value as a diagnostic tool for pneumococcal pneumonia.