Host immune responses and possible therapeutic targets for viral respiratory tract infections in susceptible populations: a narrative review.

BACKGROUND:Respiratory viruses are associated with significant global morbidity and mortality, as well as socioeconomic factors. Certain conditions and patient groups are more susceptible to develop severe viral respiratory tract infections (RTIs). OBJECTIVES:To summarise the data on deregulated immune pathways that have been associated with increased susceptibility to severe viral RTIs in certain populations. We also describe the commonalities of the defective immune pathways across these susceptible populations that may represent possible targets for future therapeutic or preventative approaches. SOURCES:We conducted free searches in Medline, Scopus, and Google Scholar for studies focusing on potential mechanisms of immune dysfunction that may be associated with severe viral RTIs in susceptible populations with conditions including pregnancy, obesity, diabetes mellitus, hypertension, cardiovascular disease, asthma, chronic obstructive pulmonary disease (COPD), chronic kidney disease, and extremes of age. We considered preclinical/animal data, original human studies, and reviews. CONTENT:Innate and adaptive immune responses become quantitatively and qualitatively compromised in aging, obesity, and diabetes mellitus, with the most pronounced changes affecting T cells. Moreover, immune dysregulation by the so-called inflamm-aging results in chronic low-grade inflammation in such conditions. Increased leptin levels affect the immune system particularly in obesity, while leptin dysregulation plays a role in asthma and COPD pathogenesis. Deficient production of interferon (IFN) type I and III in response to rhinovirus contributes to asthma exacerbations. Similar attenuation of IFN production in response to influenza and rhinovirus has been documented in pregnancy. Dampened type I IFN responses have also been found in diet-induced obese mice and in obese individuals. IMPLICATIONS:Immunosenescence and chronic low-grade inflammation accompanying aging and a variety of chronic conditions, such as diabetes, obesity, asthma, COPD, chronic renal disease, and hypertension, contribute to the poor outcomes observed following viral respiratory infections. Commonly affected pathways may represent potential future therapeutic targets.