Antigen compartmentation and T helper cell tolerance induction

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Antigen recognition is governed by peptide antigen availability and T cell receptor (TCR) affinity for peptide-MHC complexes.
• Antigen processing pathways are compartmentalized, with MHC class I presenting cytoplasmic antigens and MHC class II presenting endocytic antigens.
• This segregation may limit the diversity of self-antigens influencing T cell development and selection.

Purpose of the Study:

• To investigate the impact of antigen compartmentalization on T cell development and tolerance induction in the thymus.
• To determine if cytoplasmic or endosomal localization of self-antigens affects thymocyte selection.
• To explore the mechanisms by which antigens access the MHC class II pathway.

Main Methods:

• Generation of transgenic mice expressing pigeon cytochrome c in different cellular compartments (plasma membrane, mitochondria).
• Analysis of thymocyte development and tolerance induction in these transgenic mice.
• Use of radiation bone marrow chimeras to track antigen presentation pathways.
• Examination of thymic anatomy to correlate antigen presentation with thymocyte apoptosis.

Main Results:

• Tolerance is induced in the thymus irrespective of the antigen's cellular compartment.
• Cytoplasmic and mitochondrial antigens gain access to the MHC class II pathway via direct presentation.
• Antigen amount and TCR affinity influence the location and timing of thymocyte apoptosis within the thymus.

Conclusions:

• Antigen compartmentalization does not prevent tolerance induction in the thymus.
• Direct presentation allows cytoplasmic antigens to engage the MHC class II pathway.
• Thymocyte apoptosis timing and location are modulated by antigen load and TCR affinity, impacting T cell repertoire selection.