Question

Identify which of the following describes how antigen processing and presentation of self antigens by thymic epithelial cells differs from that of antigen-presenting cells in peripheral tissues. (Select all that apply.)

a. Thymic epithelium expresses MHC class I molecules but not MHC class II molecules.
b. Thymic epithelium uses cathepsin L for proteolytic degradation of self proteins.
c. Thymic epithelium expresses MHC class II molecules but not MHC class I molecules.
d. Thymic epithelium uses the transcription factor AIRE to activate thymic expression of tissue-specific genes.
e. Thymic epithelium expresses transcription repressor protein FoxP3.

Answer 1

Thymic epithelial cells use cathepsin L for proteolytic degradation and the transcription factor AIRE to express tissue-specific genes, which differs from peripheral APCs. They also do not express the FoxP3 protein. They express both MHC class I and II molecules, not just one type as suggested in the incorrect options.

Step-by-step explanation:

Antigen processing and presentation by thymic epithelial cells differs from that of antigen-presenting cells (APCs) in peripheral tissues in several ways. Notably:

• Thymic epithelium uses cathepsin L for proteolytic degradation of self-proteins, distinguishing it from peripheral APCs.
• Thymic epithelium uses the transcription factor AIRE to activate thymic expression of tissue-specific genes, a unique aspect compared to peripheral APCs.
• Thymic epithelium does not express the transcription repressor protein FoxP3, which is instead associated with regulatory T cells.

Thymic epithelial cells express both MHC class I and class II molecules, essential for the positive selection of developing thymocytes, which contrasts with the statement given in option a and c.