C1q binding activity in the sera of patients with chronic lung diseases.

Sera from patients with chronic lung diseases were tested for the presence of immune complexes (ICs) by the 125I-C1q-binding assay. Contrary to earlier reports, modification of the test system by addition of heparin decreased rather than increased the ability of the test to discriminate between control and pathological sera. Using the unmodified system, elevated C1q-binding activity (C1qBA) was found in patients with asthma (18%), chronic bronchitis (18%), sarcoidosis (18%), fibrosing alveolitis (50%), bronchogenic carcinoma (52%) and bronchiectasis (67%). Studies with the reducing agent 2-mercaptoethanol (2-ME) suggested a role for IgM rheumatoid factor (RF) and/or IgG-containing complexes in the C1q-reactive material of sera from patients with bronchiectasis and bronchogenic carcinoma. In the latter two groups, C1qBA was found to correlate with serum levels of IgG and IgA but not with C3 and C4. A weak condition between levels of C-reactive protein (CRP) and C1qBA was found in the bronchogenic carcinoma group. Carcinoembryonic antigen (CEA) levels were elevated in all groups studied but no correlation with C1qBA was demonstrated, suggesting that CEA and CEA-ICs, if present, do not have an influence on the C1qBA of such sera. The results indicate that elevated serum C1qBA is a concomitant of both chronic inflammatory and neoplastic diseases of the lung but the extent of any similarity in the non-immunoglobulin components of the immune complexes in the respective conditions remains unknown.