The gut immune system at homeostasis is 'tolerogenic'. This is achieved by all the following EXCEPT:
a) Presence of Tregs in the submucosal space
b) The production of cytokines such as TGF-β by resident dendritic cells
c) An ongoing production of antimicrobial peptides that limit microbiota overgrowth
d) Presence of granulocytes in the submucosal space