MHC heterozygosity limits T cell receptor variability in CD4 T cells

Area of Science:

• Immunology
• T cell biology
• Genetics

Background:

• T cell receptor (TCR) V(D)J genes generate vast TCR diversity.
• Thymocyte maturation requires specific affinity interactions with self-major histocompatibility complex (MHC)/peptides.
• MHC polymorphism influences peptide binding and T cell repertoire selection.

Purpose of the Study:

• To investigate the impact of MHC allele diversity on TCR repertoire diversity in T cells.
• To understand how thymus selection mechanisms are affected by varying MHC expression.

Main Methods:

• Comparison of TCR repertoires in CD4 T cells from mice with one versus two MHC alleles.
• Analysis of T cell receptor diversity in MHC heterozygotes and homozygotes.

Main Results:

• Mice expressing two MHC alleles exhibited reduced TCR diversity in naive CD4 T cells compared to the combined diversity of MHC homozygous relatives.
• Unexpectedly, increased MHC diversity led to a less diverse TCR repertoire.

Conclusions:

• Thymic negative selection may counteract the benefits of increased positive selection in MHC heterozygotes.
• MHC heterozygosity can result in a less diverse T cell receptor repertoire than anticipated.