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

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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.