1Central Avian Research Institute, IVRI, Izatnagar, 243 122, U.P., India.
2Division of Animal Biotechnology, IVRI, Izatnagar, 243 122, U.P., India.
The best-characterized genetic control of disease resistance and immune response in the chicken is that associated with the major histocompatibility complex (MHC). The MHC genes have a profound effect on the ability of animals to respond to specific antigens. The MHC in the chicken was first discovered as a blood group locus and is also termed the B complex. At the molecular level, the chicken MHC has unique features that will enhance its value as a marker for disease resistance i.e. the Class I and II genes overlap, therefore forming extremely tight linkage; introns are relatively small (10% of the size of most mammalian MHC); additional genes, including ones with homology to mammalian genes involved in lymphocyte activation and TAP2 (transporter associated with antigen processing) have been identified in the chicken MHC. The chicken MHC antigens perform crucial functions in the regulation of cellular communication in the immune response. The cell surface antigens of the MHC are unique to each genetically unique individual. This allows immune reactions to occur against disease organisms of an almost infinite spectrum, while simultaneously preserving the organism from self-destruction. The control of the MHC over communication events occurs at two levels: molecular interactions at the cell surface and cellular cooperation in an immune response. So the inclusion of genetic selection for disease-resistant genotypes can be a beneficial addition to a comprehensive program of disease control. Today to prevent disease in any commercial poultry business includes eradication and sanitation, minimizing environmental stressors, and employing good programs of biosecurity and vaccination. Although expensive to implement, genetic resistance has many desirable features as an approach to disease management. So in conclusion, identification of genetic markers for disease resistance can obviate the need for costly and hazardous disease-challenge testing. Enhancing immunocompetence can improve vaccine efficacy and reduce need for antibiotic treatment, thereby reducing residues.
