Age-specific different immune responses due to capabilities of secreting primal immunoglobulins responding to unexperienced antigens

Abstract

Among numerous studies on COVID-19, we noted that the infection and mortality rates of SARS-CoV-2 increased with age and that fetuses known to be particularly susceptible to infection were better protected despite various mutations. Hence, we established the hypothesis that a new immune system exists that forms before birth and decreases with aging. To prove this, we analyzed the components from early pregnancy fetal stem cells cultivated in various ex-vivo culture conditions simulating the environment during pregnancy. Resultingly, we confirmed that IgM, a natural antibody produced only in early B-1 cells, immunoglobulins including IgG3, which has a wide range of antigen-binding capacity and affinity, complement proteins, and antiviral proteins are induced. Our results suggest that fetal stem cells can form an independent immune system responding to unlearned antigens as a self-defense mechanism before establishing mature immune systems. Moreover, we propose the possibility of new solutions to cope with various infectious diseases based on the factors therein.