Circulating immune complexes in the idiopathic interstitial pneumonias.

Area of Science:

• Pulmonary Medicine
• Immunology

Background:

• Idiopathic interstitial pneumonias (IIPs) are a group of lung diseases with varying prognoses.
• The role of immune complexes in the pathogenesis of IIPs is not fully understood.

Purpose of the Study:

• To investigate the correlation between circulating immune complex levels and histopathology, immunofluorescence findings, and steroid responsiveness in patients with IIPs.
• To determine if immune complexes play a pathogenic role in cellular IIPs.

Main Methods:

• Measurement of circulating immune complex levels in 24 patients with IIPs.
• Correlation of immune complex levels with pulmonary histopathology (cellular vs. diffuse fibrosis) and immunofluorescence findings (IgG deposition).
• Assessment of radiographic and physiologic response to corticosteroid therapy in relation to baseline immune complex levels.

Main Results:

• Elevated immune complex levels were found in most patients with cellular IIPs but not in those with diffuse fibrosis (P < 0.001).
• Granular IgG deposition on immunofluorescence was more common in patients with elevated immune complex levels (P < 0.001).
• Patients with initially elevated immune complex levels showed a better response to corticosteroid therapy (P < 0.03).

Conclusions:

• Circulating immune complexes are prevalent in cellular IIPs and may contribute to disease pathogenesis.
• Elevated immune complex levels can identify a subset of patients with IIPs who are likely to respond to steroid treatment.