Soluble CD44 Is Not Elevated in Blood Products

Dr. Reinhold Munker, UCLA Cedars Sinai Medical Center, Division of Hematology/Oncology, 8700 Beverly Blvd-Davis 5019, Los Angeles, CA 90048-1804 (USA) Blood transfusion can be immunosuppressive: this may manifest itself as enhanced graft survival after renal transplantation [1] and may be associated with an enhanced rate of infection or tumor recurrence after surgery for cancer [2]. The mechanism of immunosuppression appears to involve cellular components of blood, especially lymphocytes: for example in patients waiting for renal transplantation it was shown that blood transfusion with common HLA types or shared HLA-B and DR antigens induces tolerance to donor antigens [3]. An alternative explanation may be that immunosuppression is mediated by soluble factors in blood products [4]. Recently, the involvement of the cell surface adhesion molecule CD44 in tumor metastasis was characterized [5, 6]. CD44 is expressed on many different cell types including hemato-poietic cells. An isoform of CD44 promotes metastasis in lymphoma cells [7] and soluble CD44 is elevated in the sera of patients with metastatic cancer [8] and untreated malignant lymphoma [9]. We speculated that soluble CD44 may be involved in the mechanism of immune suppression by blood transfusion and we therefore measured two isoforms of CD44 in blood products. Supernatants from various blood products were obtained by centrifugation at 400 g and frozen immediately at -80°C. Serum samples from the same blood donors were obtained by clotting at room temperature, centrifugation at 200 g and also stored at -80°C. Packed red cells were prepared with standard methods and anti-coagulated with CPDA-1 at 4-6 °C. Red cells of all ABO groups were represented and studied 4-21 days after donation. Platelet concentrates were prepared with Cobe Spectra and Baxter CS 3000 blood cell separators and Table 1. Concentration of soluble CD44 in blood products (mean ± standard deviation, ng/ml) Type of blood product Concentration Concentration soluble CD44 (Std) soluble CD44 (Var) Serum of normal blood donors 414 ± 96 (11) 168 ± 46(11) Platelet concentrates 306 ± 61 * (6) 113 + 27 (6) Packed red blood cells 115 ± 44** (9) 37 ± 17(6) Figures in parentheses represent number. * p < 5%; ** p < 0.1 %. stored at room temperature with gentle agitation. The concentration of soluble CD44 standard (Std) and CD44 variant (Var) was determined with an enzyme immunoas-say developed by Bender MedSystems, Vienna (Austria). As normal serum levels, the manufacturer indicated 443