Are Intestinal Mucins Involved in the Pathogenicity of Transmissible Gastroenteritis Coronavirus?
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Transmissible gastroenteritis virus (TGEV) is a prototype of enteropathogenic coronaviruses. The virus causes diarrhea in pigs of all ages. Infections are most severe in newborn piglets where letality can be as high as 100% (Pensaert et al 1993). The determinants of the enterotropism of TGEV are not known. A crucial factor appears to be the sialic acid binding activity of this virus (Schultze et al 1996). The ability of TGEV to attach to sialoglycoconjugates allows the virus to bind to erythrocytes. This interaction results in an agglutination reaction that probably has no physiological importance. However, hemagglutination provides a convenient assay for the sialic acid binding activity and allows quantitation of the virus. Mutants of TGEV that have lost their haemagglutinating activity because of a single point mutation in the S protein also had lost enteropathogenicity (Krempl et al 1997). Porcine respiratory Coronavirus (PRCV), a respiratory variant of TGEV also lacks hemagglutinating activity. Both PRCV and the hemagglutination-deficient mutants are still able to grow in cell culture. Therefore, the sialic acid binding activity appears to be essential for enteropathogenicity but dispensible for growth in cultured cells. The sialic acid binding activity is located on the viral surface protein S. Another binding activity of this glycoprotein is the ability to interact with aminopeptidase N, the cellular receptor for TGEV (Delmas et al 1992). PRCV and the hemagglutination-deficient mutants have retained the ability to bind to aminopeptidase N. Therefore, the interaction with aminopeptidase N — though essential for the infection of cells — does not explain the enteropathogenicity of TGEV.
KeywordsHigh Performance Liquid Chromatography Sialic Acid Newborn Piglet Sialic Acid Content Transmissible Gastroenteritis Virus
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