CELL-SURFACE PHENOTYPE AND ULTRAMICROSCOPIC ANALYSIS OF PURIFIED HUMAN ENTEROCYTES - A POSSIBLE ANTIGEN-PRESENTING CELL IN THE INTESTINE

Epithelial cells of the intestine seem to act as antigen-presenting ce lls to surrounding lymphoid tissue and may be crucial to maintain the pool of peripheral T lymphocytes. The scope of this study was to carry out an immunophenotypic and ultramicroscopic analysis of purified hum an enterocytes to elucidate their role as antigen-presenting cells, in the immune responses in the gut-associated lymphoid tissue. A method has been developed to obtain purified and viable human enterocyte popu lations, later labeled with relevant monoclonal antibodies directed to leukocyte antigens and subjected to cytofluorometric analysis. Phenot ypic analysis revealed the presence of markers common to ''classical'' antigen-presenting cells (CD14, CD35, CD39, CD43, CD63 and CD64), rei nforcing the idea that enterocytes may act as such. Moreover, several integrins (CD11b, CD11c, CD18, CD41a, CD61 and CD29) were also found. CD25 (IL-2 receptor alpha chain) and CD28, characteristic of T cells, were detected on the surface of these cells; this latter finding rises the possibility that enterocytes could be activated by IL-2 and/or vi a CD28 through binding to its ligands CD80 or CD86. Finally, the prese nce of CD21, CD32, CD35 and CD64 that may bind immune complexes via Fc or C3, suggests their participation in the metabolism of immune compl exes. Furthermore, the finding of a Birbeck's-like granule in the cyto plasm of the cells, shows that enterocytes contain an ultramicroscopic feature previously thought to be characteristic of Langerhans' cells, an antigen-presenting cell. The phenotype detected on the surface of enterocytes, along with their ultramicroscopic characteristics, sugges ts that they may play an important role in the immune responses elicit ed in the gut, presenting antigens to surrounding lymphoid cells, and establishing cognate interactions with them.