EN
Six thoroughbred horses formed a study group which was immunized twice with a vaccine (Equigrip, Rhone-Merieux), the control group was six unvaccinated horses. Blood was collected for hematological examinations, cellular immune responses, specific humoral immunity (HI) at days 0, 17, 34, 83, 117 and 123 of the experiment. On day 117 of the experiment, 3 horses of the experimental group and 3 horses of the control group were infected intranasally with a mixture of 2 subtypes (A-l and A-2) of the influenza virus. It is worth noting that 17 days after the first vaccination the lymphocyte stimulation index increased in all horses in the experimental group, while in four of the six unvaccinated horses (control) the index decreased. During this time a statistically significant increase of the specific antibodies titres was not found in vaccinated horses. Six days after the infection, the fairly high level of specific humoral immunity was accompanied by a strong stimulation of cellular immunity, which was expressed as a statistically significant increase in the lymphocyte stimulation index (as determined by the specific blastic transformation test) and was higher in vaccinated horses. Reisolation of the virus, which was attempted five days after the challenge from the nasal cavities of vaccinated horses was unsuccessful, while influenza virus subtype 2 was isolated from each of the vaccinated horses.