Coronavirus persistence in human respiratory tract and cell culture: An overview

ABSTRACT Emerging human coronaviruses, including the recently identified SARS-CoV-2, are relevant respiratory pathogens due to their potential to cause epidemics with high case fatality rates, although endemic coronaviruses are also important for immunocompromised patients. Long-term coronavirus infections had been described mainly in experimental models, but it is currently evident that SARS-CoV-2 genomic-RNA can persist for many weeks in the respiratory tract of some individuals clinically recovered from coronavirus infectious disease-19 (COVID-19), despite a lack of isolation of infectious virus. It is still not clear whether persistence of such viral RNA may be pathogenic for the host and related to long-term sequelae. In this review, we summarize evidence of SARS-CoV-2 RNA persistence in respiratory samples besides results obtained from cell culture and histopathology describing long-term coronavirus infection. We also comment on potential mechanisms of coronavirus persistence and relevance for pathogenesis.

Study on the infection of macrophage strain RAW264.7 by murine cytomegalovirus in vitro / 中华微生物学和免疫学杂志

Objective To study the feature that murine cytomegalovirus(MCMV)infect macrophage strain RAW264.7 and the influence of virus infection on proliferation and apoptosis of RAW264.7 in vitro.Methods RAW was infected by MCMV Smith with multiplicity of infection(MOI)1,0.1 and 0.01,respectivelv.The cells and culture supernatant were collected at 6,12,24,36,48,72,96 and 120 h post-infection(P.i.).Cytopathic effect(CPE)was found with microscope.Virus particles and uhrastructural changes of RAW were observed by transmission electron microscope(TEM). Early antigen(EA)expression was assaved bv immunohistochemical method.The proliferation of MCMV was studied by plaque formation assay.The influence of virus infection on proliferation and apoptosis of RAW were measured by MTT method and flow cytometry.The mouse embryo fibroblast(MEF)susceptible to MCMV infection was positive contro1.Results RAW was swollen and desquamated on 24-48 h P.i..The full-grown virus particles and swollen organelles in RAW were displayed with TEM.Preliminary positive expression of EA was demonstra ted from 6 h(MOI=1 and 0.1)to 12 h(MOI=0.01)P.i..Virus titer in RAw supernatant increased obviouslv on 24 h p.i.and reached the peak on 96-120 h P.i..The proliferation of RAW could be obviously inhibited by MCMV on 72-120 h p.i..When infected by virus with MOI=0.1,necrotic cells of RAW increased on 72-120 h D.i.and the influence of MCMV infection on apoptosis of RAW was not obvious.Conclusion Macrophage strain RAW264.7 is susceptible to MCMV,and it emerges faster cytolytic and productive infection than MEF.MCMV can inhibit the proliferation of RAW but not influence the apoptosis of it.These results can provide a practical experimental model for studying immunological pathogenic mechanism of cytomegalovirus in vitro.