Immunoglobulin G Fc Fragment‐Binding Proteins in Mycoplasma salivarium Cells

Cell proteins of Mycoplasma salivarium were separated by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, transferred to membranes, then examined for reactivity with human IgG molecules, the Fc fragment of human IgG, and concanavalin A (ConA). Multiple protein bands bound IgG, and most of them also bound ConA. One (corresponding to a molecular mass of 90 kDa) of the IgG‐ and ConA‐binding bands intensely interacted with the Fc fragment of IgG. The reactivity of proteins eluted from the band with the Fc fragment, tested by dot‐blotting and ELISA, was inhibited (90%) by pre‐incubation with IgG and to a lesser extent (50%), with IgM. Thus, M. salivarium contained a cellular protein with a molecular mass of 90 kDa, that bound the Fc fragment of human IgG.