Figure 7.

Speculative model for constitutive versus inducible M cell subsets. Top, constitutive mucosal lymphoid tissues such as Peyer’s patches and colonic patches are shown with speculative involvement of LTα1β2/LTβR and receptor activator of nuclear factor kappa-B ligand [RANKL]/RANK signalling in M cell development. Bottom, inducible mucosal lymphoid tissues are shown with speculative involvement of TNFα/TNFR2 and possible additional signals in M cell induction, and LTα1β2/LTβR signalling on stromal cells to induce RANKL expression.