| 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. |
