To evaluate the effect of SHAP on the CD44-hyaluronan interaction in a simpler system, we compared the cell adhesion activity of the SHAP-hyaluronan complex purified from pathological synovial fluid with that of free hyaluronan. The CD44-positive cutaneous T cell lymphoma cell line Hut78, known to bind strongly to hyaluronan, was used for the adhesion assay. The SHAP-hyaluronan complex or free hyaluronan was immobilized on dishes pre-coated with HABP. The cells were then added, and incubated at room temperature for 30 min. To observe significant cell adhesion, the concentration of immobilizing hyaluronan concentration had to be higher than 0.5 mg/mL; however, significant adhesion was still observed even when the concentration of the SHAP-hyaluronan complex was reduced to 0.02 mg/mL (our unpublished results). The results showed clearly that the presence of SHAP enhanced the cell adhesion. Although control experiments are necessary, the results are in line with the observation made by De La Motte et al. and further highlight the role of SHAP in cell-matrix interactions, which may be important in the pathogenesis of rheumatoid arthritis, IBD, MS, and other diseases.
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