Hyaluronan receptors in the human ocular surface: a descriptive and comparative study of RHAMM and CD44 in tissues, cell lines and freshly collected samples

The purpose of this study was to demonstrate the presence of the receptor for hyaluronan-mediated motility (RHAMM) in human conjunctival epithelium and in two widely used cell lines from human corneal (HCE) and conjunctival (IOBA-NHC) epithelia. We compared the distribution of RHAMM proteins and mRNAs in human ocular surface tissues (corneal, limbal and conjunctival), HCE and IOBA-NHC cell lines, and corneal and conjunctival epithelia primary samples from healthy donors with the previously identified hyaluronan receptor CD44. We also aimed to determine if soluble CD44 (sCD44) was present in human tears, as it could have a role in the interaction of the tear fluid with hyaluronan. Protein expression was evaluated by Western blots and immunofluorescence microscopy. mRNA expression was evaluated by RT-PCR and Q-PCR. sCD44 was analyzed by ELISA in culture supernatants and in human tears. We describe the expression of RHAMM in human healthy conjunctiva and in HCE and IOBA-NHC cells at both protein and mRNA levels, and the presence of sCD44 in human tears. Furthermore, we detected CD44 and sCD44 expression variations in in vitro inflammatory conditions. This study also focused on the necessary caution with which the conclusions extracted from cell lines should be made, and in the great value of using primary samples as often as possible.