Analytical studies of the binding parameters describing the interaction of HLA-DR epitopes with a specific...

In this paper we present an analytical study of the binding parameters related to the interactions of the HLA-DR-specific monoclonal antibody (L243) and its reacting epitope as expressed on the cell surface of seven Epstein-Barr virus-transformed B cell lines. Scatchard, Sips and Langmuir equations were used to plot and analyse the data obtained from each reaction. A single affinity constant (K) value was derived at low and high concentrations of free antibody for each antibody-cell interaction tested and was of the order of 10(7) M-1. Similar heterogeneity indices (a) (close to 1.0) and K values were obtained for most of the cells. These results suggest that the reacting HLA-DR epitopes are homogeneously distributed and equally accessible to the antibody on all the cells tested. The average number of epitopes per cell was 3.4 X 10(6), SD 0.5 X 10(6) and were similar for all the cell lines. The analytical and experimental model presented here can be useful for studying quantitative and qualitative variations in the expression of MHC epitopes in oncogenesis and disease associations.