Interindividual clinical variability in the course of SARS-CoV-2 infection is immense. We report that at least 101 of 987 patients with life-threatening COVID-19 pneumonia had neutralizing IgG auto-Abs against IFN-ω (13 patients), the 13 types of IFN-α (36), or both (52), at the onset of critical disease; a few also had auto-Abs against the other three type I IFNs. The auto-Abs neutralize the ability of the corresponding type I IFNs to block SARS-CoV-2 infection in vitro. These auto-Abs were not found in 663 individuals with asymptomatic or mild SARS-CoV-2 infection and were present in only 4 of 1,227 healthy individuals. Patients with auto-Abs were aged 25 to 87 years and 95 were men. A B cell auto-immune phenocopy of inborn errors of type I IFN immunity underlies life-threatening COVID-19 pneumonia in at least 2.6% of women and 12.5% of men.

Clinical outcome upon infection with SARS-CoV-2 ranges from silent infection to lethal COVID-19. We have found an enrichment in rare variants predicted to be loss-of-function (LOF) at the 13 human loci known to govern TLR3- and IRF7-dependent type I interferon (IFN) immunity to influenza virus, in 659 patients with life-threatening COVID-19 pneumonia, relative to 534 subjects with asymptomatic or benign infection. By testing these and other rare variants at these 13 loci, we experimentally define LOF variants in 23 patients (3.5%), aged 17 to 77 years, underlying autosomal recessive or dominant deficiencies. We show that human fibroblasts with mutations affecting this pathway are vulnerable to SARS-CoV-2. Inborn errors of TLR3- and IRF7-dependent type I IFN immunity can underlie life-threatening COVID-19 pneumonia in patients with no prior severe infection.

Significance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population.

Malnutrition is associated with a significant impairment of cell-mediated immunity, phagocyte function, immunoglobulin A concentrations and cytokine production. This situation -which is unfortunately very frequent in infants and children from developing countries -leads to a high risk of infection, and often to episodes of diarrhoea, hence aggravating the nutritional status. Fermented milks are known to exert a beneficial influence on the host's health. They act by modulating gut microflora, regulating any alteration of gut mucosa and stimulating immune response. A number of studies have shown that probiotics shorten the duration of diarrhoea and prevent recurrence of other episodes. Furthermore, probiotics can prevent diarrhoea from infection in infants with malnutrition. In addition, it has been shown that cytokines could be used as biological markers of both impaired immune system and the immune stimulation of probiotics. The aim of this review is to update the effect of fermented milks in situations of malnutrition and diarrhoea as a consequence of infection as well as the role of cytokines produced by fermented milks in these deficient conditions.

For several years cytokine production has been associated with infections but it was not suspected that some types of food could also induce cytokines, even in a state of non-infection. Lactic bacteria can induce interferon (IFN) production in human healthy subjects, thus, a better protection against infections would be expected. Therefore, we planned to evaluate the effect of two diets including yoghurt or milk on IFN-g production during nutritional recovery in two different situations of malnutrition: (1) children with diarrhoea; and (2) patients with anorexia nervosa (AN). Both the diet including yoghurt of that including milk seemed to increase IFN-g production at the end of nutritional recovery in the malnourished children with diarrhoea. The significance of interferon production and the lymphocyte subset increase should be explored to know if a better resistance against pathogens is related to them. Regulation of intestinal absorption and moderate stimulation of interferon production make the yoghurt-based diet a good choice in the nutritional care of children. In the same way, an increase in the IFN-g production was observed in AN patients consuming yoghurt. This increase of IFN-g production could be considered a biological marker to detect the effect of probiotics on the immune response, especially in the improvement of a deficient nutritional status.