| Sumario: | Respiratory syncytial virus (RSV) infects essentially all children before they reach the end of their second year of life. At least 1% of infected infants and young children are hospitalized amounting to 100,000 per year in the United States. Infections with RSV in infants range from mild rhinitis to severe bronchiolitis, pneumonia, and even death. RSV also causes upper and lower respiratory tract infections in the elderly and in immunocompromised patients. RSV entry into susceptible cells has not been fully elucidated. Two reports have concluded that a heparin-like molecule may mediate RSV infection, but they disagree on its location. Krusat et al. (1997) found that it is present on the cell surface, whereas Bourgeois et al. (1998) found that it is present on the viral envelope, not on the cell. Using a recombinant RSV that encodes the green fluorescent protein, we have developed a rapid, sensitive, quantitative system for the assessment of RSV infection by fixing cells 24-36 hr post inoculation and analyzing them by flow cytometry. We have used this system in infection studies of glycosaminoglycan (GAG) deficient cell mutants, in cells pretreated with GAG removing enzymes, and in neutralization studies with soluble, purified GAGs. We have determined the type and location of GAGs that are involve in RSV infection. We have found that two GAGs, heparan sulfate (HS) and to a lesser extent chondroitin sulfate B (CS-B), are required for efficient RSV infection, and that these critical GAGs are on the cell surface, not on the viral envelope. We have found that iduronic acid is present in the three GAGs that neutralize RSV (heparin, HS, and CS-B) but absent in three other GAGs that do not neutralize RSV, suggesting that iduronic acid plays a role in this interaction. We have found that N-sulfation, but not 6-O-sulfation or 2-O-sulfation, is required for efficient RSV infection and that the minimum heparin fragment size that can inhibit RSV infection is 10 sugar units long. In summary, cell surface HS and CS-B are critical for efficient RSV infection of cultured cells. Iduronic acid in these GAGs, and N-sulfation in HS are required for this function.
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