All ETDs from UAB

Advisory Committee Chair

Harry W Schroeder

Advisory Committee Members

Peter Burrows

Lesley Smythies

Laura Timares

Allan Zajac

Document Type

Dissertation

Date of Award

2018

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

T cell receptor (TCR) is a surface glycoprotein found on T cells that recognizes peptides bound to major histocompatibility complex (MHC) molecules (pMHC). Each TCR is a heterodimer consisting of an alpha (α) and a beta (β) chain that are created by rearrangements of variable (V), diversity (D), and joining (J) gene segments in the thymus. The most diverse component of the β chain is its third complementarity determining region, or CDR-B3. CDR-B3 is created de novo for each individual T cell by VDJ rearrangement and together with its TCRα partner, CDR-A3, creates the center of the TCR pMHC binding site. The sequences of D gene segments are highly conserved, with humans, mice, and trout having identical Dβ1 gene sequence. It is a central tenet of natural selection that the more conserved the gene sequence, the more likely the encoded protein has a critical functional role. Therefore, the goal of this study was to investigate the role of the conservation of Dβ in determining CDR-B3 content, as well as the fate and function of T cells. To do this, gene targeting was performed on mice that only possessed a single DβJβ gene segment, altering the remaining Dβ gene segment by an immunoglobulin DH with reading frames coding for tyrosine or hydrophobic amino acids, or by a novel Dβ sequence that codes for charged amino acids. Previous studies on immunoglobulin CDR-H3 (the B cell homologue to TCR) showed that similar alterations to the DH gene segment drastically changed the B cell repertoire, had deleterious effects on B cell numbers, diminished antibody production, and altered epitope recognition. We found that these changes to the Db gene segment elicited the same effects in T cells. Mutant Dβ mice had a drastically altered repertoire, were highly selected against in the periphery, and had reduced recognition of immunodominant epitopes post-vaccination. This study supports the view that the sequences of the D gene segments have undergone natural selection to counter the effect of random N nucleotide addition by constraining the core of the antigen binding site repertoire to favor the presence of specific amino acids at specific positions.

Share

COinS