Some monoclonal antibody reagents (C219 and JSB-1) to P-glycoprotein contain antibodies to blood group A carbohydrate determinants: a problem of quality control for immunohistochemical analysis.

Monoclonal antibodies (MAb) C219 and JSB-1 have been used extensively in the analysis of P-glycoprotein expression in normal and malignant tissues. This study demonstrates that some commercial lots of these MAb, even those supplied as purified immunoglobulins, contain contaminating anti-A blood group antibodies. In both sources of reagent, the antibody was specific for a particular A structure, known as repetitive or Type 3 A. These observations may account for earlier studies showing polymorphic variation in P-glycoprotein expression in epithelial tissues and an apparent correlation with the A blood type of the donor. Such reactivity can be eliminated by absorption of anti-P-glycoprotein reagents with A erythrocytes. These data re-emphasize the importance of evaluating MAb samples for unsuspected contaminating antibodies.