Immunologic responses in patients with Mycoplasma pneumoniae infections.

Serum concentrations of IgM and IgG antibodies in patients with Mycoplasma pneumoniae pneumonia were determined by means of the enzyme-linked immunosorbent assay. Analysis of serum specimens by treatment with protein A followed by fractionation on sucrose density gradient revealed for the first time the presence of rheumatoid factor in M. pneumoniae pneumonia with a remarkably high frequency. Development and persistence of the rheumatoid factor during the clinical course of this disease were also examined.