Effect of chicken infectious bronchitis vaccine on morphogenesis and differentiation of cells in caecal tonsils

The study of the chickens’ immune system morphofunctional state allows assessing critical periods of their development and the body as a whole, as well as the effectiveness of vaccine prevention methods. The purpose of this study was to identify morphological and immunohistochemical changes in the caecal tonsils of chickens aged 8, 20, 40, 90, 110 days for vaccine prevention of infectious bronchitis. During the study, the following research methods were used: cytological, histological, immunohistochemical, morphometric, light-optical, statistical. Histological preparations of caecal tonsils of poultry aged 8, 20, 40, 90, 110 days of vaccinated and unvaccinated groups were analysed and studied. Up to 20 days of age, no lymphoid nodules were detected in the caecal tonsils of chickens, both vaccinated and non-vaccinated groups. Histological and morphometric studies were conducted, which showed that vaccination of poultry accelerates the development of lymphoid formations in the early stages of the postnatal period of ontogenesis, especially in chickens aged 20 days, which is manifested by an increase in the number and size of lymphoid nodules of caecal tonsils relative to the control group. Immunohistochemical studies have established that the placement and accumulation of T-lymphocytes with markers CD4+ , CD8+ , as well as B-lymphocytes (CD20+ ) and CD45RA+ cells in caecal tonsils, namely in lymphoid nodules and diffuse accumulation of lymphoid cells, depend on the age of chickens and multiplicity of vaccinations. It was proved that in chickens aged 8 days, the number of T-lymphocyte subpopulations with surface markers CD4+ , CD8+ prevailed over CD45RA+ and CD20+ . With the increase in the number of immunizations (after three-fold vaccination against infectious bronchitis of chickens), immunocytometric studies indicated that in vaccinated chickens aged 40 and 90 days, there was a clear increase in the number of mature B-lymphocytes by 1.58 and 1.37 times, respectively. Considering the fact that the number of CD8+ lymphocytes in vaccinated chickens aged 40 days was 1.49 times greater than the number of CD4+ cells, this led to a sharp decrease in the immunoregulatory index of the caecal tonsils, which must be factored in when carrying out preventive vaccinations