Patients with ulcerative colitis (UC) who are in remission from their disease lack luminal signals capable of inducing macrophage hyporesponsiveness, which may contribute to a patient’s persistent vulnerability to relapse, according to a new study.
“Together with the distinct fecal metabolomic profile of UC patients in remission, our data suggest that UC patients may lack the signals required for proper macrophage education, rendering them vulnerable to relapse,” wrote study authors Lujain Maasfeh, PhD, of the University of Gothenburg (Sweden) and colleagues in Cellular and Molecular Gastroenterology and Hepatology.
Macrophages found in the lamina propria play a role in sustaining intestinal homeostasis. Through education by local signals, intestinal macrophages adopt a hyporesponsive phenotype and tolerogenic nature and are replenished constantly from monocytes. In patients with UC who are in remission, however, the lack of proper macrophage maturation may result in gut inflammation.
Current evidence has yet to define fully the immunomodulating determinants in the education of intestinal macrophages; however, Dr. Maasfeh and associates wrote that “intestinal microbiota and microbiota-derived metabolites increasingly are recognized for their role in imprinting tissue-specific features of intestinal macrophages.”
The researchers added that previous evidence has established that patients with UC demonstrate dysbiosis, which may impact maturation of intestinal macrophages. As such, the hyporesponsive state of intestinal lamina propria macrophages induced by the microbiota may be lost in patients with UC who are in remission, ultimately resulting in disease relapse.
To gauge the effects of fecal luminal factors on macrophage phenotype and function, the researchers extracted fecal supernatants (FS) from the fecal samples of 10 healthy volunteers and 17 patients with UC who were in remission. Following maturation of monocytes to macrophages in the presence of granulocyte-macrophage colony-stimulating factor without and with FS, the researchers assessed macrophage phenotype and function. The investigators also used gas chromatography and mass spectrometry to analyze fecal metabolomic profiles.
In healthy donors, fecal luminal factors effectively downregulated Toll-like receptor signaling, cytokine signaling, as well as antigen presentation in macrophages. In contrast, the fecal luminal factors in patients with UC demonstrated less potency in their ability to induce lipopolysaccharide hyporesponsiveness. An immune pathway scoring analysis also showed a consistently higher reaction potential among UC remission FS-treated macrophages vs. healthy FS-treated macrophages.
While FS treatment did not seem to affect the phagocytic and bactericidal abilities of macrophages, the researchers observed that the healthy FS-treated macrophages better suppressed a cluster of differentiation 4+ T-cell activation as well as interferon gamma secretion vs. FS-treated macrophages from patients with UC in remission. The FS-treated macrophages in the UC remission population also featured less potency in their ability to suppress CD4+ T-cell activation and cytokine secretion.
The authors acknowledged a few limitations, including the small sample size and the effects from using in vitro system.
“Identification of the factors involved in intestinal macrophage education is important to maintain/reestablish gut homeostasis in patients with UC,” they concluded.
The study received financial support from Swedish Research Council-Medicine, in addition to funding from a Region Västra Götaland ALF-agreement, the Knut och Alice Wallenberg Foundation Wallenberg Centre for Molecular and Translational Medicine at the University of Gothenburg, Ruth and Richard Julin’s foundation, Adlerbertska Foundation, Wilhelm and Martina Lundgren Foundation, and Apotekare Hedberg’s Foundation. The authors disclose no conflicts.