Molecular characterization of B-Lb II family (class II MHC) alleles in three strains of poultry and its association with immune response
Shanaz, Shafi (2003) Molecular characterization of B-Lb II family (class II MHC) alleles in three strains of poultry and its association with immune response. Masters thesis, College of Veterinary Science and Animal Husbandry, Anand Agricultural University, Anand, Gujarat, INDIA.
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Resistance or susceptibility to diseases is often attributable to the effects of more than one gene. However, no gene confers universal resistance to diseases since one gene may augment or cancel the effects of the other. One of the major genes governing diseases resistance is the major histocompatibility complex (MHC). It has been used as the set of candidate genes for association between DNA markers and antibody response, since it is the best characterized family of host genes that modulates immune response. Therefore, breeder can identify or use the identified haplotypes of MHC conferring resistance to particular diseases for genetic improvement and optimum returns. The present study was designed to investigate and comparatively evaluate the genetic aspects of immune response in Bantamised White Leghorn(WLH) vis-à-vis pure WLH and Bantam bird. Therefore, the present immunogenetic study involved the analysis of MHC B-Lb family (class II) alleles using one of the variants of PCR, the PCR-SSP (Polymerase Chain Reaction with sequence specific primers). Genomic DNA was isolated from blood of 36 Bantam, 36 Bantamised WLH and 36 WLH birds from CPRS, Gujarat Agricultural University, Anand. A 235 bp, exon-2region of chicken MHC B-Lb family was amplified using a set of degenerating primers. The upstream primer used was 5’CGT TCT TCT TCT RCG GTR BGA T3’ and the reverse primer was 5’ TAG TTG TGC CCG GCA GAM CSY G3’. The products of the 1st round of amplification were subjected to PCR-SSP at the specified annealing temperatures and replication cycles. The primers designed to amplify B2, B15, B19 and B21 could amplify the target sequences with the exception of primers for B13 allele producing a 222 bp, 213 bp, 213 bp and 222 bp fragments. The present research revealed nine genotypes viz., B2B2, B2B15, B2B19, B21B21, B15B15, B15B21, B15B19 B19B19 and B19B21. Allelic and genotypic frequencies differed significantly among the three genetic groups under study. It was observed that the allele B19 and B15 exhibited predominance in all the three genetic groups. Moreover, genotypic distribution also revealed abundance of B15B19 heterozygote in the selected population of birds. Immunocompetence studies were carried out to assess the immune status of the birds and correlate the antibody titers with allelic frequencies. Serum samples were collected pre- and post-vaccination with New castle disease virus, a viral antigen and inoculation with sheep red blood cells (SRBC) a particulate antigen (both used as indicator traits) on 21st, 34th, 49th and 56th day of age of chicks. Sera collected on 21st, 34th, 49th and 56th day of age of chicks was processed for antibody titers by microhaemagglutination inhibition (MHI) test while that collected against SRBC antigen on 49th and 56th day was processed by microhaemagglutination (MHA) test.Antibody titers varied significantly among three breed groups, sires, genotypes and sex. Correlations between antibody titres against NDV at different intervals were significant (P <0.05). However, a negative correlation between NDV and SRBC antibody titers were observed on 49th day of age of chicks. Immune response was studied under different genotypes and analysis revealed significant differences among Bantam, Bantamised White Leghorn birds and WLH birds. Genotype B15B19 showed highest antibody titers against NDV on 21st and 49th day of age of chicks. Immune response against intramuscularly administered SRBC (0.5ml of 1% suspension) a complex nonpathogenic T-cell dependent antigen was very low. However, significant differences in antibody titers were observed on 56th day of age of chicks. Heritability of immune response against NDV vaccine and SRBC antigen used as indicator traits were estimated by paternal half sib correlation method. The estimates showed higher S.E. values and many of the estimates were exceeding unity suggesting the greater variation within the sire, which might be due to the small size of selected sample. The present study reflected the predominance of B15 and B19 alleles among Bantam, Bantamised WLH and WLH birds, which was consistent with antibody responses against the indicator antigens (NDV and SRBC). Genotype B15B19 showed highest antibody titers on 21st day and 49th day of age, post vaccination against NDV followed by B2 B19, B2B15 and B2B2. From the above findings, it may be suggested that MHC class II (B-L) alleles B15 and B19 in the heterozygous condition are associated witha ntibody responses to NDV vaccines and particulate (T-cell) dependent antigens, SRBC. Furthermore, there exist negative correlations in mediating immune response between intramuscularly administered SRBC antigen and NDV vaccine.
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