Figure 4
From: Microfold (M) cells: important immunosurveillance posts in the intestinal epithelium
Potential routes of lumenal antigen sampling in the intestine by epithelial cell subsets and mononuclear phagocytes (MNP). (1) Sampling of gut lumenal microorganisms and macromolecules via M-cell-mediated transcytosis. (2) Although the incidence is rare in the steady state, certain inflammatory stimuli appear to recruit MNP from the lamina propria where they insert their dendrites through the tight junctions between enterocytes to directly sample the luminal contents.108, 109 (3) Another study has reported that MNP may even sample lumenal antigens by extending their dendrites directly through “transcellular pores” in the M cells themselves.7 (4) Mucin-secreting goblet cells can also function as passages for the delivery of low-molecular weight soluble antigens to CD103+ MNP in the lamina propria.107 (5) Ultrastructural analysis suggests that follicle-associated epithelia enterocytes can also acquire certain gut lumenal antigens and exocytose the intravascular contents of their large late endosomes into the extracellular space of the subepithelial dome where they are acquired by MNP.104 DC, dendritic cell.
