BACKGROUND: Celiac disease (CD) is a frequent inflammatory intestinal disease, 
with a genetic background, caused by gliadin-containing food. Some gliadin 
peptides are not digested by intestinal proteases and can have different 
biological effects. Gliadin peptides can induce innate and adaptive T 
cell-mediated immune responses. The major mediator of the stress and innate 
immune response to gliadin peptides (i.e., peptides 31-43 and 31-55) is the 
cytokine interleukin-15 (IL-15). Other peptides such as the 33 mer containing 
the P57-68 sequence, after tissue transglutaminase deamidation, are well 
presented to T cell in the intestine and can induce an adaptive immune response.
FINDINGS: In this paper, we review the recent studies on the digestion of 
gliadin and the peptides released by the digestion process. We will also discuss 
the mechanisms responsible for the internalization and transcytosis of 
indigested gliadin peptides in the intestinal epithelium.
CONCLUSIONS: Gliadin is not completely digested by the intestinal proteases 
producing bioactive peptides that have different biological effects. These 
peptides are internalized in the cells by an active process of endocytosis and 
can traverse the intestinal mucosa with different kinetics and immunological 
effects. In vivo findings will also be discussed.