Hyaluronan receptor (CD44) expression and function in human peripheral blood monocytes and alveolar macrophages

CD44 glycoproteins are present on the surfaces of many hematopoietic cells and in some cases can bind hyaluronan, a major component of the extracellular matrix. In the present study, we have found that newly explanted human peripheral blood monocytes (PBMs) exhibit a major CD44 band of 85 kDa, whereas autologous alveolar macrophages (AM phi) express multiple isoforms ranging from 85 to 200 kDa. Within 4 h in culture, PBMs began expressing new CD44 isoforms of 120, 150, and 180 kDa. Newly explanted AM phi specifically bound [3H]hyaluronan (135 cpm/microgram protein), but newly explanted PBMs did not. However, in vitro cultured PBM progressively acquired the ability to bind [3H]hyaluronan and exhibited specific binding of hyaluronan similar to that of AM phi (113 cpm/microgram protein) after 4 days in culture. In both case, the binding of [3H]hyaluronan was specifically inhibited by the addition of monoclonal antibody directed against CD44. AM phi readily degraded [3H]hyaluronan and reached a plateau after 4 days in culture (115 cpm/microgram protein). Newly explanted PBM exhibit no hyaluronan degradation and only a small degradative activity after 4 days in culture (6 to 11 cpm/microgram protein). Thus, CD44 expression and function appear to change as PBM mature in vitro resembling more that found in AM phi.