Differential usage of carbohydrate co-receptors influences cellular tropism of Theiler's murine encephalomyelitis virus infection of the central nervous system.

Theiler's murine encephalomyelitis viruses (TMEV) are ubiquitous pathogens of mice, producing either rapidly fatal encephalitis (high-neurovirulence strains) or persistent central nervous system infection and inflammatory demyelination (low-neurovirulence strains). Although a protein entry receptor has not yet been identified, carbohydrate co-receptors that effect docking and concentration of the virus on the cell surface are known for both TMEV neurovirulence groups. Low-neurovirulence TMEV use alpha2,3-linked N-acetylneuramic acid (sialic acid) on an N-linked glycoprotein, whereas high-neurovirulence TMEV use the proteoglycan heparan sulfate (HS) as a co-receptor. While the binding of low-neurovirulence TMEV to sialic acid can be inhibited completely, only a third of the binding of high-neurovirulence TMEV to HS is inhibitable, suggesting that high-neurovirulence strains use another co-receptor or bind directly to the putative protein entry receptor. Four amino acids on the surface (VP2 puff B) of low-neurovirulence strains make contact with sialic acid through non-covalent hydrogen bonds. Since these virus residues are conserved in all TMEV strains, the capsid conformation of this region is probably responsible for sialic acid binding. A persistence determinant that maps within the virus coat using recombinant TMEV is also conformational in nature. Low-neurovirulence virus variants that do not bind to sialic acid fail to persist in the central nervous system of mice, indicating a role for sialic acid binding in TMEV persistence. Analysis of high-neurovirulence variants that do not bind HS demonstrates that HS co-receptor usage influences neuronal tropism in brain, whereas, the HS co-receptor use is not required for the infection of spinal cord anterior horn cells associated with poliomyelitis.