Introduction Inflammatory bowel disease (IBD) is thought to be dependent on cell populations of the mononuclear phagocyte (MNP) system; monocytes, macrophages and dendritic cells (DCs). However, it is not yet fully understood how these functionally different MNP populations contribute to IBD immunopathogenesis. To address this, it is necessary to identify the functional and phenotypic attributes of the different human intestinal MNP populations.
Methods Fresh colonoscopic biopsies were taken, after signed informed consent, from patient with Crohn’s disease, ulcerative colitis and controls undergoing polyp surveillance scope. Biopsies were rapidly transferred to the lab for analysis. Using 12 parameter flow cytometry we have developed new strategies to identify and differentiate human intestinal MNPs, to enhance our understanding of their involvement in IBD.
Results Within the colonic lamina propria, we unambiguously differentiate macrophage populations from dendritic cells (DCs: CD64− HLA-DR+ CD11c+; macrophages: CD64+ CD206+ HLA-DR+). The colonic macrophages homogeneously express CD33 and CD68, two previously reported markers of human macrophages. Furthermore, we demonstrate heterogeneous expression of CD14 within this macrophage population. Further characterisation of the colonic macrophages identified two distinct groups, identifiable by their differential expression of the mannose receptor, CD206. To address the characteristics of these macrophage populations we assessed their proliferation, by measuring Ki67 expression. Surprisingly, all populations were found to proliferate at higher than expected levels, both in the steady state and during inflammation.
Conclusion We have developed novel protocols to isolate and identify MNP populations from human intestinal lamina propria. Human macrophages exhibit significant levels of proliferation under steady state conditions, and in samples from patients with IBD.
Disclosure of Interest None Declared