Germline-enforced enrichment for charged amino acids in TCR beta chain (TCR β) complementarity determining region 3 (CDR-B3) alters T cell development, repertoire content, and antigen recognition

AbstractT cell receptor beta chain (TCR β) diversity (Dβ) gene segments are highly conserved across evolution, with trout Dβ1 sequence identical to human and mouse Dβ1. A key conserved feature is enrichment for glycine in all three Dβ reading frames (RFs). Previously, we found that replacement of mouse Dβ1 with a typical immunoglobu lin DH sequence, which unlike D β is enriched for tyrosine, leads to an increase in the use of tyrosine in TCRβ complementarity determining region 3 (CDR-B3) after thymic selection, altering T cell numbers, CDR-B3 diversity, and T cell function. To test whether the incorporation of charged amino acids into the Dβ sequence in pl ace of glycine would also influence T cell biology, we targeted the TCRβ locus with a novel glycine-deficientDβDKRQ allele that replaces D β1 coding sequence with charged amino acids in all three reading frames. Developing T cells usingDβDKRQ expressed TCR CDR-B3s depleted of tyrosine and glycine and enriched for germline-encoded lysine, arginine, and glutamine. Total thymocytes declined in number during the process of β selection that occurs during the transition from the DN3bc to DN4 stage. Conventional thymocyte and T cell numbers remained reduced at all subsequent thymic stages and in the spleen. By contrast, regulatory T cell numbers were increased in Peyer’s patches and the large intestine. In terms of fu nctional consequences, T cell reactivity to an ovalbumin immunodominant epitope was reduced. These...

Source: Immunogenetics - April 29, 2023 Category: Genetics & Stem Cells Source Type: research