TCR Reserve: A Novel Principle of CD4 T Cell Activation by Weak Ligands

Abstract

Some ligand-receptor systems have a receptor reserve where a maximal response can be achieved by occupation of a fraction of available receptors. An implication of a receptor reserve is the expansion of the number of ligands for response. To determine whether T cells follow receptor reserve, we have characterized the effect of reducing TCR levels on CD4 T cell responses elicited by altered peptide ligands that vary in potency. Agonist peptide is unaffected by a 90% reduction in TCR level while proliferation to weak agonists is significantly inhibited when TCR expression is reduced by 40%. Thymocyte-negative selection similarly demonstrates a differential requirement of TCR for response to agonist, weak agonist, and partial agonist. Therefore, our data demonstrate receptor reserve as a novel principle of T cell activation in which excess TCRs expand the antigenic repertoire to include less potent ligands.

NADPH Oxidase Modifies Patterns of MHC Class II–Restricted Epitopic Repertoires through Redox Control of Antigen Processing

“…It could be argued that was assessed using MOG in a reconstituted system with increasing concentrations of H 2 O 2 . Following incubation at 37˚C, relative quantities of remaining substrate (MOG ) and cleavage products (MOG [42][43][44][45][46][47][48][49][50][51][52][53][54][55] and MOG [35][36][37][38][39][40][41] ) were quantified by reverse-phase HPLC following peak identification by MALDI-TOF MS. Data are presented as the abundance of the cleavage product MOG [42][43][44][45][46][47][48][49][50][51][52][53][54][55] relative to MOG (corresponding destruction of the I-A b binding region) and was calculated using the following formula: RPA = (P x /S x )/(P 0 /S 0 ), where RPA indicates relative peptide abundance; P x indicates product (MOG [42][43][44][45][46][47][48][49][50][51]…”

“…To achieve this, T cell hybridomas were first stably transfected with an NFA-T-enhanced IL-2 promoter-driven eGFP construct, followed by multiple rounds of selection by FACS to enrich those hybridoma clones that expressed eGFP only following presentation of their cognate peptide epitope by APCs (25). When added to BMMfs that were previously pulsed with HEL protein, we found that WT and Cybb 2/2 BMMfs were equally able to induce eGFP expression in two of the hybridomas (Hb1.9 and H46.13), indicating that the processing/presentation efficiency of HEL [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and HEL [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] peptides were unaffected by NOX2 (Fig. 2D).…”

“…The relative abundance of the peptides was quantified using the area under corresponding peaks. Abundance of the cleavage product MOG [42][43][44][45][46][47][48][49][50][51][52][53][54][55] relative to MOG (corresponding destruction of the I-A b binding region) was calculated using the following formula: RPA = (P x /S x )/(P 0 /S 0 ), where RPA indicates relative peptide abundance, P x indicates product (MOG [42][43][44][45][46][47][48][49][50][51][52][53][54][55] ) of sample, S x indicates substrate (MOG ) of sample, P 0 indicates product (MOG [42][43][44][45][46][47][48][49][50][51][52][53][54][55] ) without hydrogen peroxide, and S 0 indicates substrate (MOG ) without hydrogen peroxide.…”

“…In brief, BMMfs and BMDCs derived from WT and NOX2-deficient mice were allowed to endocytose unprocessed whole Ag or preprocessed antigenic peptides for a defined period. The activation of CD4 + T cells isolated from OTII and 2D2 mice and coincubated with the APCs were assessed by measuring surface expression of the early activation markers CD69 and CD25 as previously described (15,25,31,33,35,53,54).…”

“…To further interrogate the ability of NOX2 to alter processing patterns of a single Ag, we measured the efficiency of WT and Cybb 2/2 BMMfs to process four distinct HEL epitopes (HEL [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] , HEL [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] , HEL [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] , and HEL 74-90 ) from whole HEL protein and present them to epitope-specific CD4 + T cell hybridomas (Hb1.9, H30.44, H46.13, and B04, respectively) (26). To achieve this, T cell hybridomas...…”