Immunoassays have been recently developed that measure the avidity of IgG antibodies to complex microbial antigens and are suitable for serologic diagnosis of infectious diseases. In these avidity ELISAs, protein-denaturing agents are applied either as diluents of patient sera to prevent the immune complexing of IgG (diluting principle), or the preformed complexes are treated with the protein denaturants (eluting principle). We compared four protein denaturants previously used in such assays, in a diagnostic avidity ELISA for rubella IgG. Diethylamine, guanidine, thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate at an optimum pH. Patient sera obtained recently after primary infection were distinguished from sera representing past rubella immunity by any protein denaturant tested by the eluting principle, which was superior to the diluting principle.
Normal serum PAP levels on admission to the hospital in patiens with acute pancreatitis has been proposed to help select the patients who are not going to develop complications. The aims of this study were, first, to assess the specificity of serum pancreatitis associated protein (PAP) serology test and second, to evalute the usefulness of the test for prediciting complications in acute pancreatitis on admission to the hospital. The sensitivity of the PAP ELISA in patiens with acute pancreatitis on admission to the hospital was 70% and the serum PAP levels significantly higher than in healthy controls (p < 0.0001). However, the serum PAP levels in patients with acute pancreatitis were not significantly different from values in patients with various abdominal diseases (p < 0.58). Serum PAP levels gave good correlation to APACHE II (p = 0.02) and CRP (p = 0.01). Two patients with local complications (necrotizing pancreatitis, pancreatic fluid collection) had elevated serum PAP levels on admission to the hospital (> 100 ng/ml). The diagnostic specififity of PAP ELISA is low. Patients, who develop local complications in acute pancreatitis can not be excluded by normal serum PAP levels on admission to the hospital.
Amount and avidity of serum IgG antibodies to Pseudomonas aeruginosa exotoxin A in sera of 31 patients with cystic fibrosis (CF) was studied. Eight patients had P. aeruginosa isolated from the sputum on multiple occasions, while from 23 patients no P. aeruginosa was isolated. Amount of IgG antibodies to P. aeruginosa exotoxin A were significantly increased in the serum of patients with P. aeruginosa pulmonary colonization (p<0.0001). On the contrary, serum IgG avidity in the colonized and in the non-colonized CF patients was low (<10) and was statistically different when compared to the 30 age-matched healthy controls (p<0.0001). There was no change in IgG avidity in six chronically infected CF patients from whom we obtained serum samples after half a year period (p=0,55).
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