Circulating immune complexes in patients with mycoplasmal pneumonia.

Circulating immune complexes as measured by conglutinin (IgG-IC) and IgM rheumatoid factor (IgM-RF) were studied in 114 patients with mycoplasmal pneumonia (58 inpatients and 56 outpatients). The levels of IgG-IC and IgM-RF of the patients were significantly higher than those of 13 healthy control subjects. In addition, the levels of IgG-IC of the inpatients were significantly higher than those of the outpatients. The highest titers of IgG-IC were obtained 9 to 30 days after onset of disease, and the levels of IgG-IC were elevated during the time period when pulmonary changes were pronounced. The levels of IgM-RF were irrelevant to infiltration on chest radiographs. An analysis using density gradient centrifugation showed that the decrease of IgG-IC with intermediate size was associated with improvement of the disease. A possible pathogenic role of IgG-IC in mycoplasmal pneumonia is discussed.