Evaluation and enhancement of chicken cell-mediated immunity in Marek's disease virus infection

The evolving nature of Marek's disease virus (MDV) has promoted the emergence of higher virulence strains causing increased MD economical losses. Because outbreaks cannot be prevented through vaccination, a multiple trait selection of MD resistant chickens is urged. The purpose of this research was to evaluate and enhance the chicken cell mediated immunity, particularly the NK-like cell activity, and determine its response to Marek's disease virus infection. To achieve this purpose, multiple experimental studies were performed using standard NK cell and MHC-restricted cytotoxicity chromium release assays, direct immunostaining of spleen cells and standard virological procedures.; The inherent NK cell activity of broiler lines was compared and the immune enhancement via NK cell function of different oral compounds was evaluated. There was a differential NK cell activity between the broiler lines that exactly correlated with their reported resistance to infectious diseases, and a beta-carotene positive modulation of NK cell function. Immunophenotyping of spleen cells showed a sex-related beta-carotene modulation of T-cell antigens and major histocompatibility complex (MHC) molecules, likely by enhancement of the immune system maturation, suggesting that females may have a delayed immune maturity.; The effects of beta-carotene in MDV infection were further assessed. The spleen cells from beta-carotene supplemented MDV inoculated birds had increased NK cell activity, reduced infection rate and decreased proportion of activated CD4 cells compared to non-modulated MDV-infected chicken splenocytes, showing high correlation with a decrease in MD severity. It is proposed beta-carotene functions through direct enhancement of NK cell function and/or macrophage activation, promoting a proinflammatory cytokine loop and increased nitric oxide levels. The latter may decrease MDV replication with downregulation of immune response that decreased activation of CD4+ cells. Therefore, there are fewer targets for neoplastic transformation.; Using resistant and susceptible inbred lines, it was determined that resistant birds had earlier and more sustained NK cell and MHC-restricted cytotoxicity than susceptible chickens, whose responses were delayed, transient and markedly reduced. The resistant birds showed superior NK cell function. We concluded that selection and modulation of a higher inherent NK cell activity may be beneficial in MD control.