Decline in specificity of the ELISA due to storage of serum, and its recovery by adsorption with kaolin

Pathogenetic and serological aspects of pulmonary aspergillosis

Af is an important pathogen of the bronchopulmonary system, and the clinical spectrum encompasses aspergilloma, CNPA, IPA, ABPA, bronchial asthma, and allergic alveolitis. Bronchial carriage may, however, not always be associated with pathological effects. The polymorphism of the aspergillus-related disorders seems mostly to depend upon the different responses of the hosts. This review considers the antigenic composition of Af and specific antibody responses in man in relation to the pathogenesis and diagnosis of the various forms of pulmonary aspergillosis. More than 200 macromolecular components have been listed for Af and more than 30 antigens found to react with human sera. Serum antibodies to Af are common in healthy subjects. Schønheyder and his associates (A-L) have shown that IgG, IgA and IgM antibodies in healthy subjects are directed towards antigens to which also patients with aspergillosis strongly react. With immunofluorescent staining these antigens were found to be associated with hyphal walls, and a MW 470,000 fraction from ruptured mycelium was most reactive in ELISA. The respiratory tract appears to be the major route for exposure since the humoral responses include IgA class antibodies, and sIgA antibodies are found in bronchial secretions. Moreover, IgG antibody levels to the MW 470,000 fraction correlate with occupational exposure and smoking habits. In patients with cystic fibrosis high IgG antibody levels to MW 470,000 and MW 25,000-50,000 antigen fractions were associated with the carriage of Af in the sputum. An individual patient's level of IgA antibodies to the MW 470,000 fraction was inversely related to the Af carrier rate, and this was also true for IgE dependent reactivity to Af antigens. These observations indicate that IgG antibodies to some antigens mirror the extent of antigenic exposure, whereas some IgA and IgE antibodies may play a protective role against bronchial colonization with Af. IgG antibody determinations by ELISA were found to provide a higher diagnostic efficacy in pulmonary aspergillosis than IgA antibody assays. With IgG antibodies there were statistically significant differences between patients and the controls and there was little overlap of ELISA values between the groups. The fractions of MW 250,000 with catalase activity and MW 25,000-50,000 with protease activity, were most suitable for serological diagnosis. A gel immunoelectrophoretic assay proved Af catalase to be a major diagnostic antigen in patients with aspergilloma or with an apical aspergillus lung infiltrate.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-term storage of peroxidase-labelled immunoglobulins for use in enzyme immunoassay

Optimal conditions for long-term storage of peroxidase-labelled immunoglobulins for use in enzyme immunoassays have been investigated with particular emphasis on the preservation of the immunological and enzyme activity. Immunoglobulin G preparations from different animal species were purified according to conventional methods and labelled with horseradish peroxidase. Conjugates were stored at different temperatures either in liquid form with 50% glycerol, after lyophilization or as ammonium sulphate precipitates. In addition, the conjugates were also frozen and stored at -40 degrees C. The immunological and enzymatic activity of the conjugates was evaluated at regular intervals throughout storage. The best results were obtained with conjugates stored as ammonium sulphate precipitates at 4 degrees C. Under these conditions, the complexes retained after 2 years of storage 92 and 91% of their enzymatic and immunological activity respectively and gave excellent reproducibility in ELISA. The conjugates exhibited a very low degree of self-aggregation. The ammonium sulphate did not interfere in the ELISA. Storage at elevated temperatures resulted in a greater decrease in enzymatic than immunological activity but the results obtained with the ammonium sulphate precipitates were clearly superior to those obtained with alternative storage procedures. The estimated half life of the whole enzymatic-immunological activity of conjugates at 4 degrees C was 9 years. The stability of both activities at 25 degrees C was also reasonably good for short periods. Conjugates stored for 40 days at 37 degrees C lost 60% enzyme activity but retained unaltered their immunological activity and gave rise to high blanks in the ELISA, due to auto-aggregation.

Elimination of nonspecific cytomegalovirus immunoglobulin M activities in the enzyme-linked immunosorbent assay by using anti-human immunoglobulin G

Direct enzyme-linked immunosorbent assay methods offer several advantages in assessing past or recent exposure to cytomegalovirus (CMV) infection, but there persist many pitfalls in the use of these methods for determining specific immunoglobulin M (IgM). The efficiency of absorption of sera by IgG-coated latex beads, aggregated human IgG, or Staphylococcus aureus, i.e., for removing nonspecific CMV IgM activities, was evaluated in comparison with the effect of an anti-human IgG hyperimmune serum. Large routine series comprising serum samples from patients of various clinical groups and healthy individuals were examined. The CMV IgM-positive samples were at first treated with latex or aggregated IgG, but these absorptions left too many CMV IgM-positive individuals. S. aureus increased the nonspecific activity of some sera and, in other cases, removed or impaired specific IgM activities. The anti-IgG treatment caused the disappearance of nonspecific CMV IgM activities that had resisted the other treatments, whereas specific activities remained intact. Utilizing this method, only 1.03% of the routine series patients remained CMV IgM positive by the enzyme-linked immunosorbent assay, a figure in good agreement with a mean probability of CMV antibody acquisition of 0.33% for the population living in Belgium. On the other hand, in a series of patients who were investigated for serological response to several viruses, eight individuals displayed multiple IgM activities after anti-IgG treatment. In these cases, most IgM activities were found in patients who had IgG toward the related antigen for a long time before transient IgM was detected. This result implies that to assess a diagnosis of primary infection, it is necessary to examine serial specimens for IgG acquisition accompanying specific IgM.

Antibody to early and late antigens of herpes simplex virus type 1 in patients with oral cancer

HEp-2 cells were infected with herpes simplex virus type 1 (HSV-1) and harvested at selected times thereafter. IgG, IgA, and IgM antibody to virus antigens present in these cells at each time was measured in sera from oral cancer patients, and in matched controls. The IgA response of oral cancer patients was significantly greater than that of controls both at 8 and at 48 hours after infection, but showed no difference in response to HSV-1 virus particles. IgM antibody detected two peaks of antigen synthesis, at 4 and 48 hours after infection. Oral cancer patients had a stronger IgM response than did controls to both early and late peaks; the latter was significant at the 5% level. Oral cancer patients also had a significantly higher IgM response to the virus particle. These results imply the existence of at least two different HSV-1 antigens associated with oral cancer. Both are late antigens; one is recognized by IgA, and the other is recognized by IgM antibody.