Demonstration of cryoprecipitable immune complexes in pneumococcal pneumonia

Cold-insoluble protein complexes (cryoprecipitates) can be found in the serum in a variety of infectious diseases. We studied serum cryoprecipitates isolated from three patients with pneumococcal pneumonia by counterimmunoelectrophoresis (CEP) and immunofluorescent technics for the presence of immune complexes. The cryoprecipitates and supernatant serum were tested for pneumococcal capsular polysaccharide (PCP) by CEP at 37 C and 56 C with the appropriate controls. Antibodies against PCP in the cryoprecipitates and the supernatant serum were detected as follows. Streptococcus pneumoniae from each case was fixed onto slides. The slides were incubated with each cryoprecipitate and supernatant serum at 37 C, and further incubated with fluorescein isothiocyanate-conjugated antisera to human IgG, IgM, and IgA. The slides were examined with an immunofluorescent microscope. PCP was demonstrated in all of the cryoprecipitates. IgG antibodies against PCP were detected in all of the cryoprecipitates, while IgM antibodies were detected in Cases 1 and 2, and IgA antibodies in Case 1 only. Complement components of C3 and C4 also were demonstrated in the cryoprecipitates by CEP. These findings suggest that some patients with pneumococcal pneumonia have cryoprecipitable-immune complexes consisting of PCP and its antibodies.