Effect of heparin on infection of cells by porcine reproductive and respiratory syndrome virus.

OBJECTIVE: To investigate whether heparin has any effect on the growth of porcine reproductive and respiratory syndrome virus (PRRSV). SAMPLE POPULATION: 2 isolates of PRRSV, and as control viruses, 1 isolate of pseudorabies virus (PRV) and 1 isolate of parainfluenza 3 virus (PIV-3). PROCEDURES: Plaque assays, using a continuous cell line (MARC-145) derived from African green monkey kidney cell line (MA104), were performed for determination of inhibitory effect of heparin on PRRSV, PRV, and PIV-3. The effect of various doses of heparin and heparinase on the growth of PRRSV, PRV, and PIV-3 was evaluated and compared. In each experiment, value were expressed as the mean value for duplicate samples. RESULTS: The number of plaques formed by PRRSV and PRV was reduced to 24 to 25 and 15% of the untreated control (100%), respectively, by 1 U of heparin/ml, but could not be reduced below 6 to 7 and 3%, respectively, by use of concentrations up to 50 U/ml. An inhibitory effect of heparin, at a concentration up to 50 U/ml, was not observed on PIV-3. Delaying addition of heparin for 30 minutes after the addition of PRRSV and PRV reduced plaque formation by 48 to 51 and 68%, respectively, compared with 91 to 92 and 95%, respectively, if heparin was added at the time of infection. In addition, most PRRSV added was retained by heparin beads, as was PRV. Heparinase treatment of MARC-145 cells reduced the number of PRRSV-, as well as PRV-induced plaques. On the other hand, the number of PIV-3-induced plaques did not decrease after treatment of MARC-145 cells with heparinase. CONCLUSIONS: Addition of heparin to PRRSV or to the MARC-145 cells before virus inoculation and treatment of the cells with heparinase prevented the virus from infecting the cells.