Possible role of Streptococcus pyogenes in mucocutaneous lymph node syndrome. XI. Immunoelectron microscopic observation of protoplast-like "spherical bodies" detected in peripheral blood of MCLS patients.

Protoplast-like "spherical bodies" averaging 0.5-1.5 microns in diameter and devoid of cell walls were first detected by Ueno et al, in the buffy coat of heparinized venous blood from patients with mucocutaneous lymph node syndrome (MCLS). But the nature of the "bodies" has yet to be clarified because of the absence of convincing evidence pointing to their antigenic characteristics. The present investigations were designed solely to provide a serological identification of the "bodies" by the use of immunoelectron microscopy, with the following results. First, "spherical bodies" bearing a striking resemblance to those observed by the above-mentioned authors were detected in biopsy specimens from challenge sites in mice infected with Streptococcus pyogenes as well as in the buffy coat of peripheral blood from MCLS patients. Second, the "bodies" detected were stained distinctly in both cases by an immunohistochemical technique using, as the primary antibody, a rabbit antiserum raised toward S. pyogenes-derived protoplasts, which was then absorbed with protoplasts from Staphylococcus aureus and Escherichia coli. Third, the absorbed sera were proved to be not faultless, because complete specificity toward protoplasts from S. pyogenes was not attained due to the presence of a large amount of cross-reactive antigens between protoplasts from the immunizing and absorbing strains of bacteria. The implications of these findings are discussed, particularly in relation to the evaluation of the present serological test for the "spherical bodies".