A DIFFERENT PROFILE OF EPITOPIC DOMINANCE IN THE IMMUNOGLOBULIN-G RESPONSE TO BOVINE BETALACTOGLOBULIN IN LUNG-CANCER

Background. The authors previously documented a quantitative defect in the immunoglobulin G (IgG) response toward bovine betalactoglobulin ( BLG), the major cow's milk antigen, and antigen pi of the house dust m ite, Dermatophagoides pteronyssinus (Der p1), in patients with lung ca ncer. In the Der pi model, the authors documented at the IgG level an epitope specificity that differed between patients with lung cancer (p referential specificity for cryptic epitopes) and healthy control subj ects and patients with mite allergy. The current study investigated wh ether this varying specificity might be extended to the IgG response t oward BLG. Methods. The authors compared the IgG binding to native BLG (nBLG) and its products of pepsin hydrolysis (dBLG) in a solid-phase enzyme-linked immunosorbent assay (ELISA) using peroxidase-conjugated protein A in 120 patients with lung cancer, 52 patients with chronic o bstructive pulmonary disease (COPD) who were closely matched for age, sex, and smoking habits with the patients with cancer, and 120 healthy control subjects (blood donors). Results. Expressing the ratio betwee n optical densities observed for dBLG and nBLG, respectively, the auth ors documented two groups: patient with lung cancer with higher levels of binding on dBLG (mean ratio +/- SD, 1.66 +/- 0.26) and healthy con trol subjects and patients with COPD with similar levels of retention for dBLG and nBLG (mean ratios +/- SD, 1.00 +/- 0.10 and 1.01 +/- 0.07 , respectively). Influence of population characteristics could be excl uded. The histologic type of cancer and its extent had no influence on the defined ratio. Conclusion. These results suggest a preferential r ecognition of epitopes unmasked by pepsin hydrolysis (cryptic epitopes ?) by lung cancer IgG, contrasting with the preferential specificity o f IgG from healthy control subjects and patients with COPD for structu ral epitopes unaffected by the proteolysis. These findings are similar to those observed previously with Der pi and indicate a varying, and possibly specific, profile of epitopic dominance in the IgG response t o antigens naturally presented at the mucosal level in patients with l ung carcinoma, a model of mucosal cancer.