Fulminant Viral Hepatitis in Two Siblings with Inherited IL-10RB Deficiency

Genetic defects of brain immunity in childhood herpes simplex encephalitis

Herpes simplex virus 1 (HSV-1) encephalitis (HSE) is the most common sporadic viral encephalitis in humans. It is life-threatening and has a first peak of incidence in childhood, during primary infection. Children with HSE are not particularly prone to other infections, including HSV-1 infections of tissues other than the brain. About 8-10% of childhood cases are due to monogenic inborn errors of 19 genes, two-thirds of which are recessive, and most of which display incomplete clinical penetrance. Childhood HSE can therefore be sporadic but genetic, enabling new diagnostic and therapeutic approaches. In this Review, we examine essential cellular and molecular mechanisms of cell-intrinsic antiviral immunity in the brain that are disrupted in individuals with HSE. These mechanisms include both known (such as mutations in the TLR3 pathway) and previously unknown (such as the TMEFF1 restriction factor) antiviral pathways, which may be dependent (for example, IFNAR1) or independent (for example, through RIPK3) of type I interferons. They operate in cortical or brainstem neurons, and underlie forebrain and brainstem infections, respectively. Conversely, the most severe inborn errors of leukocytes, including a complete lack of myeloid and/or lymphoid blood cells, do not underlie HSE. Thus congenital defects in intrinsic immunity in brain-resident neurons that underlie HSE broaden natural host defences against HSV-1 from the leukocytes of the immune system to other cells in the organism.

Non-canonical IL-22 receptor signaling remodels the mucosal barrier during fungal immunosurveillance

Mucosal barrier integrity is vital for homeostasis with commensal organisms while preventing pathogen invasion. We unexpectedly found that fungal-induced immunosurveillance enhances resistance to fungal outgrowth and tissue invasion by remodeling the oral mucosal epithelial barrier in mouse models of adult and neonatal Candida albicans colonization. Epithelial subset expansion and tissue remodeling were dependent on interleukin-22 (IL-22) and signal transducer and activator of transcription 3 (STAT3) signaling, through a non-canonical receptor complex composed of glycoprotein 130 (gp130) coupled with IL-22RA1 and IL-10RB. Immunosurveillance-induced epithelial remodeling was restricted to the oral mucosa, whereas barrier architecture was reset once fungal-specific immunity developed. Collectively, these findings identify fungal-induced transient mucosal remodeling as a critical determinant of resistance to mucosal fungal infection during early stages of microbial colonization.

Human life within a narrow range: The lethal ups and downs of type I interferons

The past 20 years have seen the definition of human monogenic disorders and their autoimmune phenocopies underlying either defective or enhanced type I interferon (IFN) activity. These disorders delineate the impact of type I IFNs in natural conditions and demonstrate that only a narrow window of type I IFN activity is beneficial. Insufficient type I IFN predisposes humans to life-threatening viral diseases (albeit unexpectedly few) with a central role in immunity to respiratory and cerebral viral infection. Excessive type I IFN, perhaps counterintuitively, appears to underlie a greater number of autoinflammatory and/or autoimmune conditions known as type I interferonopathies, whose study has revealed multiple molecular programs involved in the induction of type I IFN signaling. These observations suggest that the manipulation of type I IFN activity to within a physiological range may be clinically relevant for the prevention and treatment of viral and inflammatory diseases.

In search of a function for human type III interferons: insights from inherited and acquired deficits

The essential and redundant functions of human type I and II interferons (IFNs) have been delineated over the last three decades by studies of patients with inborn errors of immunity or their autoimmune phenocopies, but much less is known about type III IFNs. Patients with cells that do not respond to type III IFNs due to inherited IL10RB deficiency display no overt viral disease, and their inflammatory disease phenotypes can be explained by defective signaling via other interleukine10RB-dependent pathways. Moreover, patients with inherited deficiencies of interferon-stimulated gene factor 3 (ISGF-3) (STAT1, STAT2, IRF9) present viral diseases also seen in patients with inherited deficiencies of the type I IFN receptor (IFNAR1/2). Finally, patients with autoantibodies neutralizing type III IFNs have no obvious predisposition to viral disease. Current findings thus suggest that type III IFNs are largely redundant in humans. The essential functions of human type III IFNs, particularly in antiviral defenses, remain to be discovered.

Hepatitis A virus infection

Hepatitis A is a vaccine-preventable infection caused by the hepatitis A virus (HAV). Over 150 million new infections of hepatitis A occur annually. HAV causes an acute inflammatory reaction in the liver that usually resolves spontaneously without chronic sequelae. However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure. Host factors, such as immunological status, age, pregnancy and underlying hepatic diseases, can affect the severity of disease. Anti-HAV IgG antibodies produced in response to HAV infection persist for life and protect against re-infection; vaccine-induced antibodies against hepatitis A confer long-term protection. The WHO recommends vaccination for individuals at higher risk of infection and/or severe disease in countries with very low and low hepatitis A virus endemicity, and universal childhood vaccination in intermediate endemicity countries. To date, >25 countries worldwide have implemented such programmes, resulting in a reduction in the incidence of HAV infection. Improving hygiene and sanitation, rapid identification of outbreaks and fast and accurate intervention in outbreak control are essential to reducing HAV transmission.

Autoantibodies Neutralizing Type III Interferons Are Uncommon in Patients with Severe Coronavirus Disease 2019 Pneumonia

Autoantibodies (AABs) neutralizing type I interferons (IFN) underlie about 15% of cases of critical coronavirus disease 2019 (COVID-19) pneumonia. The impact of autoimmunity toward type III IFNs remains unexplored. We included samples from 1,002 patients with COVID-19 (50% with severe disease) and 1,489 SARS-CoV-2-naive individuals. We studied the prevalence and neutralizing capacity of AABs toward IFNλ and IFNα. Luciferase-based immunoprecipitation method was applied using pooled IFNα (subtypes 1, 2, 8, and 21) or pooled IFNλ1-IFNλ3 as antigens, followed by reporter cell-based neutralization assay. In the SARS-CoV-2-naive cohort, IFNλ AABs were more common (8.5%) than those targeting IFNα2 (2.9%) and were related with older age. In the COVID-19 cohort the presence of autoreactivity to IFNλ did not associate with severe disease [odds ratio (OR) 0.84; 95% confidence interval (CI) 0.40-1.73], unlike to IFNα (OR 4.88; 95% CI 2.40-11.06; P < 0.001). Most IFNλ AAB-positive COVID-19 samples (67%) did not neutralize any of the 3 IFNλ subtypes. Pan-IFNλ neutralization occurred in 5 patients (0.50%), who all suffered from severe COVID-19 pneumonia, and 4 of them neutralized IFNα2 in addition to IFNλ. Overall, AABs to type III IFNs are rarely neutralizing, and do not seem to predispose to severe COVID-19 pneumonia on their own.

Human inherited complete STAT2 deficiency underlies inflammatory viral diseases

STAT2 is a transcription factor activated by type I and III IFNs. We report 23 patients with loss-of-function variants causing autosomal recessive (AR) complete STAT2 deficiency. Both cells transfected with mutant STAT2 alleles and the patients' cells displayed impaired expression of IFN-stimulated genes and impaired control of in vitro viral infections. Clinical manifestations from early childhood onward included severe adverse reaction to live attenuated viral vaccines (LAV) and severe viral infections, particularly critical influenza pneumonia, critical COVID-19 pneumonia, and herpes simplex virus type 1 (HSV-1) encephalitis. The patients displayed various types of hyperinflammation, often triggered by viral infection or after LAV administration, which probably attested to unresolved viral infection in the absence of STAT2-dependent types I and III IFN immunity. Transcriptomic analysis revealed that circulating monocytes, neutrophils, and CD8+ memory T cells contributed to this inflammation. Several patients died from viral infection or heart failure during a febrile illness with no identified etiology. Notably, the highest mortality occurred during early childhood. These findings show that AR complete STAT2 deficiency underlay severe viral diseases and substantially impacts survival.