Hyper IgM Globulinemia Associated with Pneumonia due to Mycoplasma pneumoniae

The level of serum IgM has been found to be increased in covalescent stage of M. pneumpniae infection. Thirty-two children with pneumonia due to M. pneumoniae were evaluated for serum IgM level and the contribution of M. pneumoniae antibodies and cold agglutinins to the raised IgM level was assessed. All of the 32 had elevated serum IgM levels (>140mg/dl) in convalescent stage. The serum IgM level was significantly correlated with M. pneumoniae titer (r=0.54) and also with cold agglutinin titer (r=0.59). IgM secreting cells in patients' peripheral blood had no correlation with serum IgM levels. The high IgM convalescent sera absorbed with protein A revealed high M. pneumniae titer. The sera absorbed with M. pneumoniae antigen revealed no antibodies to M. pneumoniae or cold agglutinins, but still showed high IgM levels. Immunoelectrophoresis demonstrated polyclonal IgM increase. These data suggest that serum. IgM increase in M. pneumoniae infection is of polyclonal response. A large part of the IgM increase would seem to be attributable to non -specific immunoglobulin production.