Immunoglobulin M rheumatoid factor in patients with mycoplasmal pneumonia.

The relation of IgM rheumatoid factor (IgM-RF) and IgG immune complex (IgG-IC) to clinical aspects of mycoplasmal pneumonia was studied. Serial serum samples obtained from 20 patients with mycoplasmal pneumonia and 4 patients with Mycoplasma pneumoniae infection but without pneumonia were analyzed by sucrose density gradient centrifugation and ELISA. In this study, the following findings were obtained. With the peak concentration of IgM-RF, there was a decrease in pulmonary infiltration concomitant with a decrease in active IgG-IC. With a rapid decrease in IgM-RF, there was an exacerbation concomitant with an increase in active IgG-IC. In some cases the concentrations of IgM-RF were low in the acute phase of the disease and increased in the convalescent phase. Some patients with continuously low concentrations of IgM-RF had prolonged pneumonia. The existence of IgG-IgM-RF complexes in the bloodstream was shown. In this report, it is suggested that IgM-RF might be associated with the recovery or might play a role in the recovery from this pneumonia. Other possible explanations are also discussed.