Tools to study pathogen-host interactions in bats

Abstract

Bats are natural reservoirs for a variety of emerging viruses that cause significant disease in humans and domestic animals yet rarely cause clinical disease in bats. The co-evolutionary history of bats with viruses has been hypothesized to have shaped the bat-virus relationship, allowing both to exist in equilibrium. Progress in understanding bat-virus interactions and the isolation of bat-borne viruses has been accelerated in recent years by the development of susceptible bat cell lines. Viral sequences similar to severe acute respiratory syndrome corona virus (SARS-CoV) have been detected in bats, and filoviruses such as Marburg virus have been isolated from bats, providing definitive evidence for the role of bats as the natural host reservoir. Although viruses can be readily detected in bats using molecular approaches, virus isolation is far more challenging. One of the limitations in using traditional culture systems from non-reservoir species is that cell types and culture conditions may not be compatible for isolation of bat-borne viruses. There is, therefore, a need to develop additional bat cell lines that correspond to different cell types, including less represented cell types such as immune cells, and culture them under more physiologically relevant conditions to study virus host interactions and for virus isolation. In this review, we highlight the current progress in understanding bat-virus interactions in bat cell line systems and some of the challenges and limitations associated with cell lines. Future directions to address some of these challenges to better understand host-pathogen interactions in these intriguing mammals are also discussed, not only in relation to viruses but also other pathogens carried by bats including bacteria and fungi.

Novel Insights Into Immune Systems of Bats

“…Studies with these isolates [MERS-CoV/ EMC2012 (26,59), Nipah virus/ Bangladesh/ human/ 2004/ Rajbari R1 (68) and Nipah virus/ Malaysia/ human/ 1000/ PKL (68)] do not represent true virus-host interactions that are occurring in the natural setting. Given the limitations and challenges associated with isolating viruses from bats (138), these studies represent our best understanding of these interactions. Isolating bat viruses, such as recently discovered bat ebolaviruses (6,7,139) and propagating them in relevant bat cells will represent true virushost interactions and selection pressure.…”

“…The limited repertoire of cell lines from few species of bats and their tissues have led to studies where viruses have been propagated and studied in cell lines that are derived from unrelated or closely related species of bats. This important topic was recently reviewed by us and a call for collaboration and sharing of resources was put out to advance bat-virus interaction studies at a faster pace (138). Similarly, inability to isolate majority of the "detected" bat viruses have led to studies in bats and bat cells with human isolates of closely related viruses (24,26).…”

“…Most infection studies in bats and bat cells have used human isolates or virus stocks that have been propagated in non-bat cell lines (138). Propagating viruses in non-natural hosts generates adaptive mutations, such as mutations that were detected during sequential passages of Marburg virus in mice and cell-culture (150).…”

Infection of bat and human intestinal organoids by SARS-CoV-2

“…Except for three strains isolated using interferon (IFN)-deficient Vero E6 or Vero cells 13,14 and one strain of genetically synthesized virus 15 , to date, most identified bat SARSr-CoVs have not been successfully isolated and cultivated. Despite many reports of bat primary cell cultures and immortalized bat cell lines 16 , as well as the commercially available bat cell lines in ATCC, isolation of SARSr-CoV using a bat cell line has never been documented.…”

“…However, no direct evidence exists of SARSr-CoV infection in these bats, which might be owing to the nature of acute and self-limiting infection, seasonal fluctuation of virus growth in these bats 18 and the difficulty in accessing these animals in the wild. Thus, the absence of a readily accessible in vitro model that can faithfully represent native bat cells is a major obstacle to isolate and study bat viruses 16 , including bat SARSr-CoVs, which are predicted to possess high zoonotic potential 15 .…”