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Natural killer (NK) cells are innate lymphoid cells that protect a host from viral infections and malignancies. MicroRNA‐146a (miR‐146a) is an important regulator of immune function that is highly expressed in NK cells and is further upregulated during murine cytomegalovirus (MCMV) infection. Here we utilized mice with a global targeted deletion of miR‐146a to understand its impact on the innate immune responses to MCMV infection. MiR‐146a−/− mice were protected from lethal MCMV infection, which was intrinsic to the hematopoietic compartment based on bone marrow chimera experiments. NK cell depletion abrogated this protection, implicating NK cells as critical for the miR‐146a−/− protection from MCMV. Surprisingly, NK cells from miR‐146a‐deficient mice were largely similar to control NK cells with respect to development, maturation, trafficking, and effector functions. However, miR‐146a−/− mice had increased NK cell numbers and frequency of the most mature Stage IV (CD27−CD11b+) NK cells in the liver at baseline, enhanced STAT1 phosphorylation, and increased selective expansion of Ly49H+ NK cells and T cells during MCMV infection. This study demonstrates a critical role for miR‐146a in the host response to MCMV, arising from mechanisms that include increased NK cell numbers and early T‐cell expansion. [ABSTRACT FROM AUTHOR]

Objectives Takayasu arteritis (TAK) is a large-vessel vasculitis rarely reported in children and infants. Most articles on paediatric TAK have not focused on infants. We present the largest case series of infantile TAK, aiming to identify its demographic and clinical characteristics and compare them with existing data on older children. Methods We conducted an international multicentre retrospective cohort study. Epidemiological and clinical data were collected from patients' charts from six rheumatology centres. All patients met both the EULAR/PReS 2008 criteria and the 1990 ACR/EULAR criteria and were diagnosed with TAK at age <5 years. Results Twelve patients were included (50% female). Median age of symptom onset was 11 months, with a diagnostic delay of 4 months. The most common symptoms at presentation were hypertension, blood pressure differences between limbs, and fever. The most commonly involved arteries were the abdominal aorta and renal artery. Medications included steroids, conventional and biologic DMARDs, and other immunosuppressive therapies. Half of the patients received biologic agents, of which infliximab had the highest complete remission rate (40%). Other medications resulting in complete remission were CYC (40%) and MTX (38%). Invasive procedures were required for 58% of patients. The most common complications were cardiac (50%), stroke (42%), and serious infections (33%). No patients died. Conclusion This study presents the largest series of infantile TAK. Compared with other reported series on older children, infants with TAK have more severe disease and were more likely to receive biologic agents, develop complications, and require invasive interventions. [ABSTRACT FROM AUTHOR]