Human CD44std Recombinant Protein, eBioscience?. CD44 cell surface antigen is a 100 kDa type 1 transmembrane glycoprotein widely expressed on human leucocytes, white matter of the brain and by some epithelial cells of the intestine and breast. Several isoforms of CD44 exist, including the predominant CD44H isoform detected in many normal tissues. CD44 is a receptor for hyaluronic acid (HA) and is involved in cell-cell interactions, cell adhesion and migration. CD44 also participates in a wide variety of cellular functions including lymphocyte activation, recirculation and homing. CD44 expression may be up-regulated upon some carcinomas, and it has been speculated that this may be related to metastatic potential. CD44 is expressed by h