A Unique Presentation of Infantile-Onset Colitis and Eosinophilic Disease without Recurrent Infections Resulting from a Novel Homozygous CARMIL2 Variant.

PURPOSE: This study aimed to characterize the clinical phenotype, genetic basis, and consequent immunological phenotype of a boy with severe infantile-onset colitis and eosinophilic gastrointestinal disease, and no evidence of recurrent or severe infections. METHODS: Trio whole-exome sequencing (WES) was utilized for pathogenic variant discovery. Western blot (WB) and immunohistochemical (IHC) staining were used for protein expression analyses. Immunological workup included in vitro T cell studies, flow cytometry, and CyTOF analysis. RESULTS: WES revealed a homozygous variant in the capping protein regulator and myosin 1 linker 2 (CARMIL2) gene: c.1590C>A; p.Asn530Lys which co-segregated with the disease in the nuclear family. WB and IHC analyses demonstrated reduced protein levels in patient's cells compared with controls. Moreover, comprehensive immunological workup revealed severely diminished blood-borne regulatory T cell (Treg) frequency and impaired in vitro CD4+ T cell proliferation and Treg generation. CyTOF analysis showed significant shifts in the patient's innate and adaptive immune cells compared with healthy controls and ulcerative colitis patients. CONCLUSIONS: Pathogenic variants in CARMIL2 have been implicated in an immunodeficiency syndrome characterized by recurrent infections, occasionally with concurrent chronic diarrhea. We show that CARMIL2-immunodeficiency is associated with significant alterations in the landscape of immune populations in a patient with prominent gastrointestinal disease. This case provides evidence that CARMIL2 should be a candidate gene when diagnosing children with very early onset inflammatory and eosinophilic gastrointestinal disorders, even when signs of immunodeficiency are not observed.

Impaired IL-10 Receptor-mediated Suppression in Monocyte From Patients With Crohn Disease.

OBJECTIVES: Interleukin-10 (IL-10) is an immunoregulatory cytokine that has a central role in suppressing proinflammatory responses. Patients with deleterious mutations in interleukin (IL)-10 or IL-10 receptor (IL-10R) genes develop severe colitis and perianal disease in the first months of life. Whether IL-10R expression and signaling in pediatric- or adult-onset Crohn disease (CD) are altered is unknown. The objective of this study was to characterize IL-10R expression and IL-10R-mediated suppression in patients with CD. METHODS: Monocytes were sorted from peripheral blood mononuclear cells of patients with CD and control subjects. IL-10R expression was determined by flow cytometry. Monocytes were stimulated with lipopolysaccharide (LPS) for 3 hours in the presence of different concentrations of IL-10 to determine IL-10-mediated suppression of tumor necrosis factor α production. Signaling through the IL-10R was evaluated by quantifying STAT3 phosphorylation in response to IL-10 stimulation. RESULTS: Forty-two subjects were enrolled in this study: 19 with CD and 23 controls. Stimulation of monocytes with LPS markedly increased IL-10R expression in both groups but to a much lower extent in patients with CD. In addition, IL-10-mediated suppression of TNFα production upon LPS stimulation and IL-10-induced STAT3 phosphorylation were attenuated in patients with CD versus controls. Finally, LPS-stimulated monocytes from patients with CD secreted significantly lower quantities of IL-10, compared with control monocytes. CONCLUSIONS: IL-10R expression and signaling are decreased in monocytes from patients with CD. Additional studies are required to assess whether similar patterns occur in other innate immune cells, especially in the gut, and whether disease activity, medical therapy, and genetic factors modulate these findings.