Protein degradation and peptide release from milk proteins in human jejunum. Comparison with in vitro gastrointestinal simulation.

Human jejunal digests after oral ingestion of casein and whey protein were collected by a nasogastric tube and protein degradation and peptide release was compared with that found in the digests of the same substrates using a standardised protocol. No intact casein was detected in the jejunal nor in the in vitro samples taken during the intestinal phase, while ß-lactoglobulin was found in one hour-jejunal samples in agreement with the in vitro digestion. In vivo and in vitro digests showed comparable peptide profiles and high number of common sequences. A selective precipitation step was used to strengthen the identification of phosphorylated peptides. Most of the sequences found in jejunum, some of them not previously described, were also identified in the simulated digests. Common resistant regions to digestion were identified, revealing that the in vitro protocol constitutes a good approximation to the physiological gastrointestinal digestion of milk proteins.

Human intestinal pro-inflammatory CD11chighCCR2+CX3CR1+ macrophages, but not their tolerogenic CD11c-CCR2-CX3CR1- counterparts, are expanded in inflammatory bowel disease.

Although macrophages (Mϕ) maintain intestinal immune homoeostasis, there is not much available information about their subset composition, phenotype and function in the human setting. Human intestinal Mϕ (CD45+HLA-DR+CD14+CD64+) can be divided into subsets based on the expression of CD11c, CCR2 and CX3CR1. Monocyte-like cells can be identified as CD11chighCCR2+CX3CR1+ cells, a phenotype also shared by circulating CD14+ monocytes. On the contrary, their Mϕ-like tissue-resident counterparts display a CD11c-CCR2-CX3CR1- phenotype. CD11chigh monocyte-like cells produced IL-1ß, both in resting conditions and after LPS stimulation, while CD11c- Mϕ-like cells produced IL-10. CD11chigh pro-inflammatory monocyte-like cells, but not the others, were increased in the inflamed colon from patients with inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis. Tolerogenic IL-10-producing CD11c- Mϕ-like cells were generated from monocytes following mucosal conditioning. Finally, the colonic mucosa recruited circulating CD14+ monocytes in a CCR2-dependent manner, being such capacity expanded in IBD. Mϕ subsets represent, therefore, transition stages from newly arrived pro-inflammatory monocyte-like cells (CD11chighCCR2+CX3CR1+) into tolerogenic tissue-resident (CD11c-CCR2-CX3CR1-) Mϕ-like cells as reflected by the mucosal capacity to recruit circulating monocytes and induce CD11c- Mϕ. The process is nevertheless dysregulated in IBD, where there is an increased migration and accumulation of pro-inflammatory CD11chigh monocyte-like cells.