The evolution and maintenance of polymorphism in the major histocompatibility complex

Area of Science:

• Immunogenetics
• Animal Science
• Parasitology

Background:

• The ovine major histocompatibility complex (MHC) plays a crucial role in immune responses.
• Previous studies indicated a link between MHC alleles and nematode resistance in sheep.
• Genetic variation within the MHC is known to influence disease resistance.

Purpose of the Study:

• To confirm the association between specific ovine MHC DRB1 alleles and nematode egg counts.
• To investigate the role of MHC variation in genetic resistance to nematode infections.
• To explore the impact of heterozygote advantage on MHC polymorphism and parasite resistance.

Main Methods:

• Analysis of faecal nematode egg counts in lambs.
• Genotyping of the ovine MHC class II DRB1 locus.
• Comparison of nematode resistance between lambs with different MHC genotypes (G2 vs. I alleles, homozygotes vs. heterozygotes).

Main Results:

• Lambs with the G2 allele at the ovine MHC DRB1 locus exhibited lower faecal nematode egg counts compared to those with the I allele.
• This association was consistently observed across separate lamb cohorts from the same farm.
• Heterozygotes for MHC alleles demonstrated increased resistance to nematodes compared to homozygotes.

Conclusions:

• Variation within the ovine MHC significantly contributes to the genetic basis of nematode resistance.
• The G2 allele at the MHC DRB1 locus is associated with enhanced nematode resistance in lambs.
• Heterozygote advantage at MHC loci is a key factor in maintaining MHC polymorphism and driving parasite resistance.