RÉSUMÉ
Infectivity titre of IBR virus in MDBK cells using monolayer, suspension and roller system revealed that the roller system produced the highest infectivity titre with an increase of log[10] 1.0 than their corresponding monolayer cell culture. On the other hand, the infectivity titres in cell suspension cultures were log[10] 0.6-log[10] 0.8 lower than their corresponding monolayer cell culture system. Influence of DEAE-dextran for the enhancement of IBR virus infectivity in different cell culture systems, 25 microg DEAE-dextran per ml is considered the safest concentration to the MDBK and VERO cell lines and giving these results: 1- Infectivity titre of IBR virus was markedly increased under the effect of both serial passages and DEAE-dextran in MDBK and VERO cells which showed an increase of log[10] 1.2 and log[10] 1.0, respectively more than their respective non treated passages. 2- In the roller system, DEAE-dextran enhanced the growth of virus by about 0.9, 0.7 log[10] more than growth of untreated virus in both MDBK and VERO cell lines, respectively. 3- The highest titre obtained when using DEAE-dextran MDBK roller system was log[10] 9.2 TCID[50]/ml