M cells in the follicle-associated epithelium of the rabbit conjunctiva preferentially bind and translocate latex beads.

PURPOSE: This study investigates the presence of M cells in the rabbit conjunctiva. Resolving whether the conjunctiva contains M cells is important, because at other mucosal sites, these antigen sampling cells are known to initiate the mucosal immune response and to act as a site of entry for opportunistic pathogens.

METHODS

Fluorescent 0.2-microm polystyrene latex beads were either instilled into the conjunctival sac for 20 to 120 minutes in vivo or applied to flat mounts in vitro. Specimens were assessed by epi-fluorescence stereomicroscopy, widefield fluorescence microscopy, confocal scanning laser microscopy, and transmission and scanning electron microscopy.

RESULTS

Latex beads preferentially bound to a subpopulation of cells in the epithelium overlying mucosal lymphoid follicles in the fornix region. At 4 degrees C, the beads were associated with the apical surface of cells that had longer, more irregular microvilli than the surrounding epithelial cells. Within 20 minutes of an in vivo exposure, latex beads were internalized by the follicle-associated epithelial cells and with time moved into the underlying follicle region. After 120 minutes of in vivo exposure, latex beads could be found in cervical lymph nodes.

CONCLUSIONS

This study demonstrates that the follicle-associated epithelium of the rabbit conjunctiva contains a cell with morphologic characteristics and the ability to bind and translocate latex beads, which make it indistinguishable from antigen sampling M cells in the rabbit cecum and tonsils. Consistent with its hypothesized antigen sampling role, beads that have been translocated by this cell are rapidly transferred to cervical lymph nodes.