IN-VITRO CULTURE OF HUMAN PERIPHERAL-BLOOD MONOCYTES INDUCES HYALURONAN-BINDING AND UP-REGULATES MONOCYTE VARIANT CD44 ISOFORM EXPRESSION

CD44 is a cell surface proteoglycan homologous to cartilage link prote in that serves as a receptor for hyaluronan (HA). CD44 isoforms includ e an unspliced 80- to 90-kDa standard form (CD44S) and isoforms derive d from alternative splicing of nine CD44 variant exons (CD44V). Ligati on of CD44 isoforms on monocytes induces the production of IL-1 and TN F-alpha. In addition, CD44 mAbs and HA inhibit HIV infection of monocy tes by monocytotropic HIV, but do not inhibit T cell tropic HIV infect ivity of T cells. To determine the ability of PB lymphocytes and monoc ytes to bind HA and to define and compare CD44 isoforms present on PB monocytes and lymphocytes, we studied PBMC using a panel of CD44 mAbs, HA-FITC, flow cytometry, and Western blot analysis. We found that fre shly isolated PB monocytes and lymphocytes did not bind soluble HA. Ho wever, in vitro culture of PBMC for 8 to 16 h resulted in CD44-depende nt HA-FITC binding to monocytes, but not to lymphocytes. Western blot and flow cytometry analyses using CD44 mAbs demonstrated selective exp ression of high m.w. CD44V isoforms on cultured monocytes, but not on lymphocytes. Finally, tissue macrophages and multinucleated giant cell s from patients with inflammatory lesions expressed CD44V6- and CD44V9 -containing CD44 isoforms in vivo, suggesting that CD44V expression is associated with differentiation of monocytes to tissue macrophages in vivo in inflammatory sites. Taken together, our data demonstrate that PB monocytes, but not T or B lymphocytes, acquire the ability to bind HA and up-regulate CD44V expression after in vitro culture.