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 [H-3]hyaluronan (135 cpm/mu g protein), but newly explanted PBMs did not. However, in vitro cultured PBM progressively acquired the ability to bind [H-3]hyaluronan and exhibited specific binding of hyaluronan similar to that of AM phi (113 cpm/mu g protein) after 4 days in culture. In both cases, the binding of [H-3]hyaluronan was specifically inhibited by the addition of monoclonal antibody directed against CD44. AM phi readily degraded [H-3]hyaluronan and reached a plateau after 4 days in culture (115 cpm/mu g protein). Newly explanted PBM exhibit no hyaluronan degradation and only a small deg radative activity after 4 days in culture (6 to 11 cpm/mu g protein). Thus, CD44 expression and function appear to change as PBM mature in vitro resembling more that found in AM phi.