Although the gel precipitation method is valuable in the diagnosis of patients with aspergillosis, it is not infrequently negative in a certain number of cases of histologically and bacteriologically confirmed pulmonary aspergilloma. This is probably due to insufficient sensitivity. Because of these reasons, we developed a new paper disc solid phase immunoradiometric assay (IgG-IRA) to detect IgG type antibody specifically against Aspergillus fumigatus in sera with reasonable sensitivity.
New procedures which we developed were as follows; purification of anti-human IgG heavy chain antibody from goat labelled with ¹²⁵I with an affinity chromatography on Sepharose 4B column conjugated with human IgG, and a surface treatment of paper discs conjugated with Aspergillus fumigatus antigen with goat gammaglobulin. These procedures are essential to reduce background due to nonspecific binding of antibody. As a comparative study, we simultaneously carried out gel precipitation tests with double diffusion method and immunoelectrophoresis using same sera.
These studies were carried out in 101 subjects composed of 33 pulmonary aspergilloma patients, 36 non-aspergillosis patients with various respiratory diseases and 32 normal adults. In all pulmonary aspergilloma patients, %cpm of IgG-IRA were significantly greater than in the other two groups (p<0.001). In normal subjects and non-aspergillosis patients, %cpm of IgG-IRA were low and there was no significantly statistical difference between the two. Mean %cpm of IgG-IRA of pulmonary aspergilloma patients with positive gel precipitation tests was significantly greater than those of aspergilloma patients with negative gel precipitation tests (p<0.001). The sensitivity and the specificity of IgG-IRA were both 100% in pulmonary aspergilloma patients and control groups. On the other hand, the sensitivity and the specificity of gel precipitation tests were 76% and 100% respectively.
From these results, it may conclude that the newly developed IgG-IRA method is highly sensitive and specific for IgG type antibody to A. fumigatus, and patients with pulmonary aspergilloma respond to aspergillus infection with the production of specific IgG antibody even when it is not detected with gel precipitation tests.