Enhancement of natural killer cell activity by Marek's disease vaccines¹

Abstract

Vaccination against Marek's disease with herpesvirus of turkeys (HVT) has been reported to cause increased natural killer (NK) cell activity as detected in vitro against LSCC-RP9 target cells. The effect of vaccination with SB-1 (a nononcogenic chicken herpesvirus), HVT and the HVT/SB-1 combination on NK cell activation was compared in Marek's disease susceptible (P-2) and resistant (N-2) chickens. Birds were vaccinated at 7 days of age and NK cell activity was measured between 3 and 42 days after vaccination. Both SB-1 and HVT caused a significant increase in NK cell-induced specific release. The increase was similar in N-2 and P-2 chickens for either HVT or SB-1, while the combined vaccine induced a significantly higher increase in N-2 compared to P-2 birds. The maximal effect of vaccination on NK cells was detected at 7 days after vaccination. In contrast with the results in young birds, vaccination of birds between 31 and 45 days of age caused either no effect or a suppression rather than an enhancement in NK cell activity.