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-activated killer (LAK) cell-mediated cytolysis of bladder tumour cells. Soluble ICAM-1 was isolated by immunoaffinity chromatography using two different anti-ICAM-1 monoclonal antibody (mAb) columns from normal human serum, bladder tumour cell culture supernatants and the urine of patients receiving bacillus Calmette-Guerin (BCG) immunotherapy for bladder cancer. Soluble ICAM-1 from all sources resolved as a single diffuse band with a molecular weight of 80 to 90 kilodaltons (kDa) on Western blots under both non-reducing and reducing conditions, consistent with the predicted molecular weight for monomeric sICAM-1. Monomeric sICAM-1 isolated from serum retained its ability to inhibit the binding of an anti-ICAM-1 mAb to ICAM-1 positive target cells. In contrast, monomeric sICAM-1 isolated from serum and urine failed to inhibit LAK cell-mediated cytolysis of four bladder tumour cell lines. These results are in agreement with recent observations that the monomeric form of sICAM-1 binds to its receptor LFA-1 with extremely low affinity, indicating that at physiological concentrations sICAM-1 does not interfere in ICAM-1/LFA-1 mediated cellular adhesion events.

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