PURIFICATION AND CHARACTERIZATION OF SOLUBLE INTERCELLULAR-ADHESION MOLECULE-1 (SICAM-1) AND ITS EFFECT ON CELL-MEDIATED CYTOLYSIS OF TUMOR-CELLS

The aim of this study was to determine the effects of highly purified soluble ICAM-1 (sICAM-1) from a variety of sources on lymphokine-activ ated killer (LAK) cell-mediated cytolysis of bladder tumour cells. Sol uble ICAM-1 was isolated by immunoaffinity chromatography using two di fferent anti-ICAM-1 monoclonal antibody (mAb) columns from normal huma n serum, bladder tumour cell culture supernatants and the urine of pat ients receiving bacillus Calmette-Guerin (BCG) immunotherapy for bladd er cancer. Soluble ICAM-1 from all sources resolved as a single diffus e band with a molecular weight of 80 to 90 kilodaltons (kDa) on Wester n blots under both non-reducing and reducing conditions, consistent wi th the predicted molecular weight for monomeric sICAM-1. Monomeric sIC AM-1 isolated from serum retained its ability to inhibit the binding o f an anti-ICAM-1 mAb to ICAM-1 positive target cells. In contrast, mon omeric sICAM-1 isolated from serum and urine failed to inhibit LAK cel l-mediated cytolysis of four bladder tumour cell lines. These results are in agreement with recent observations that the monomeric form of s ICAM-1 binds to its receptor LFA-1 with extremely low affinity, indica ting that at physiological concentrations sICAM-1 does not interfere i n ICAM-1/LFA-1 mediated cellular adhesion events.