Effect of homologous delayed hypersensitivity testing on specific and non-specific lymphoblastic transformation in cattle latently infected with bovine rhinotracheitis virus (bovine herpesvirus 1, BHV 1).

Two cattle latently infected with infectious bovine rhinotracheitis virus (Bovine herpesvirus 1, BHV 1) were intradermally injected with inactivated BHV 1 antigen (delayed hypersensitivity test, DHT, skin test). Another animal, free of BHV 1 infection was similarly treated. Two latent carriers of the virus, intradermally injected with Phosphate-Buffered Saline solution were used as control. The evolution of spontaneous multiplication of lymphocytes and lymphoblastic transformation in vitro induced by three phytomitogens (con A, PHA, PWM) and BHV 1 antigen was followed in all animals. The delayed hypersensitivity test provoked an increase in spontaneous lymphocyte multiplication in latent carriers as well as an increase in mitogen- and antigen-induced blastogenesis on the 2nd and the 9th day following the treatment. A similar increase occurred on the 9th day in the BHV 1-free animal. Therefore, in latent carriers of BHV 1, delayed hypersensitivity testing induces an anamnestic lymphocyte reaction corresponding to the cutaneous one. This first lymphocyte activity is followed, one week later, by a new reaction which occurs both in infected and uninfected animals.