LATERAL ORGANIZATION OF THE ICAM-1 MOLECULE AT THE SURFACE OF HUMAN LYMPHOBLASTS - A POSSIBLE MODEL FOR ITS CODISTRIBUTION WITH THE IL-2 RECEPTOR, CLASS-I AND CLASS-II HLA MOLECULES

Lateral distribution of the ICAM-1 molecule and its topological relati onship (mutual proximity) to the heavy and light chains of class I HLA molecules, HLA-DR and interleukin-2 receptor alpha-chain (IL-2R alpha ) were studied in the plasma membrane of HUT-102B2 T and JY B lymphobl astoid cell lines by the technique of flow cytometric energy transfer (FCET). Effects of adherency and treatments with recombinant interfero n-gamma or tumor necrosis factor-alpha on the relative expression leve l of ICAM-1 to the above cell surface proteins were also investigated. While the cytokines did not significantly affect the ICAM-1 level of either cell line, an increased ICAM-1 expression was found on adherent JY cells. The ICAM-1 expression varied significantly with the cell cy cle and culture conditions, as well. The statistical analysis of the d ifferences observed in the energy transfer efficiency histograms resul ted in a possible model of lateral co-distribution of these proteins i n the plasma membrane. These two-dimensional patterns proved to be dif ferent for T and B lymphoma lines. ICAM-1 molecules showed a high degr ee of self-association on HUT-102B2 (T) cells, while they were mainly expressed as monomers on the surface of JY (B) cells. Both cells showe d a significant (ca. 30%) difference between densities of the heavy an d light chains of class I HLA antigen, suggesting a substantial amount of beta 2-microglobulin free heavy chains on these cell lines. The cl ass I HLA molecules also showed partial self-association, but on both cell lines. The beta(2)-microglobulin and the heavy chain of the class I HLA showed strongly different proximities to the IL-2R alpha, HLA-D R and ICAM-1 molecules, indicating that their orientations relative to the other proteins are dissimilar. IL-2R alpha molecules of the HUT-1 02B2 (T) cells are located mostly in the vicinity of the beta(2)-micro globulin. In contrast, the local density of HLA-DR antigens is higher in the proximity of the heavy chain than in the vicinity of the beta(2 )-microglobulin. The possible functional significance of these protein patterns is also discussed herein.