Konrad Thorsteinsson, a PhD student in our lab, has been working in collaboration with Inga Rimkute, a previous PhD student in the lab of professor Göran Larson (University of Gothenburg), to investigate the role of different histo-blood groups in norovirus infections. This fruitful collaboration resulted recently in a publication in the Journal of Biological Chemistry, entitled “Histo-blood group antigens of glycosphingolipids predict susceptibility of human intestinal enteroids to norovirus infection”. (DOI:10.1074/jbc.RA120.014855)
Norovirus is one of the major causes of gastrointestinal infections worldwide, estimated to cause around 20 % of all gastrointestinal infections. The disease causes acute vomiting and/or diarrhea, which can last for several days. Although many people recover on their own without medical assistance, the disease presents a particular danger for infants, the elderly, and people with compromised immune system. In the developing world, the virus presents additional dangers. Since norovirus infections cause dehydration, outbreaks in countries with lack of access to drinking water can have excessive mortality rates. It is estimated that 200.000 children under the age of 5 die every year due to norovirus infections.
Research into norovirus is difficult, because until recently there was no way to culture human noroviruses in a laboratory setting. Most research has involved patient challenge studies, where patients are exposed to viruses shed from infected people, and the disease onset studied. This changed in 2016 when the research group of Mary K. Estes (Baylor College of Medicine, Houston, Texas, USA) reported a cell culture system, termed human intestinal enteroids. This system utilizes stem cells harvested from patients’ intestinal crypts, which are then cultured as miniature models of the intestine. Using these enteroid cells, they were able to culture human noroviruses in vitro for the first time in history.
Using this enteroid system, it was observed that some enteroid cells show susceptibility to norovirus infection, while others do not. The differences are believed to be related to different histo-blood group antigen expressions of the cells. Histo-blood group antigens are sugar molecules found on the surface of some cells, such as red blood cells and cells found in the human intestine and are the determining factor of a person’s blood type. Research into norovirus has determined that people with different blood types show different susceptibilities to norovirus infection. The cause for these differences is unknown but is believed to be due to the different binding behavior of the virus to cells with these sugar molecules.
In collaboration with the Estes lab, Inga Rimkute studied the histo-blood group antigen expression and lipid composition of several different enteroid cell types, originating from different patients, to attempt to determine the differences that can explain why some of them can sustain norovirus replications while other cannot. To complement these experiments, Konrad ran a fluorescent binding assay to study how virus-like particles of human norovirus interact with membranes from enteroid cells, and how the interaction differs between lipid membranes from susceptible and non-susceptible cells. Using fluorescently labelled vesicles made from the extracted lipids, and a microscopy method known as TIRF (Total Internal Reflection Fluorescence), Konrad was able to study virus binding and release to enteroid membranes in real-time, on a single particle scale, and was able to determine clear differences in the binding patterns of vesicles from susceptible cells versus non-susceptible cells.
Overall, this work has demonstrated the high importance of the role of histo-blood group antigens in the norovirus infectious cycle and brings us one step closer in understanding the mechanism behind norovirus infectivity.