MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-IV RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM MARKERS IN REPLICATED MEAT-TYPE CHICKEN LINES DIVERGENTLY SELECTED FOR HIGH OR LOW EARLY IMMUNE-RESPONSE

Information on MHC may improve the efficiency of selection for immunol ogical traits via the application of marker assisted selection or by s electing directly for a specific restriction fragment length polymorph ism (RFLP) band or MHC haplotype. An experimental procedure is present ed here for identifying MHC genes that are related to early immune res ponse. A Class IV cDNA clone was used to probe Southern blots of eryth rocyte genomic DNA from chickens. Chickens were taken from the second (S2) and third (S3) generations of replicated lines divergently select ed for high antibody response (HC1, HC2) or low antibody response (LC1 , LC2) to Escherichia coli vaccination at 10 days of age. These select ion criteria have been found to be associated with other immunological parameters. The hypothesis that these selected lines differ in their MHC loci was evaluated by comparing the frequencies of MHC RFLP marker s (single RFLP bands) and haplotypes (patterns of RFLP bands). The sig nificant differences between LC and HC in the frequency of many MHC RF LP bands and of five MHC haplotypes indicate that early antibody produ ction is influenced by MHC genes. The reliability of the association b etween the selection and frequency differences was tested and proven i n most cases by analysis of the replicated lines. These differences in RFLP markers represent a change in allelic frequencies in MHC genes, probably due to selection. The results imply a connection between the Class IV genes and early antibody production, and they show the potent ial of prospective breeding not only by immunological phenotype but al so by genotype (i.e., using RFLP markers of the MHC).