Which of the following cell surface molecules is classified as an MHC class II antigen?

Which of the following cell surface molecules is classified as an MHC class II antigen?

• A. HLA-A
• B. HLA-B
• C. HLA-C
• D. HLA-DR

Answer: (D)

MHC class II antigens are primarily involved in presenting processed antigens to CD4+ T cells, which play a crucial role in the immune response. Among the options listed, HLA-DR is classified as an MHC class II molecule. HLA-DR is expressed on professional antigen-presenting cells, such as dendritic cells, macrophages, and B cells. These molecules are essential for initiating and regulating immune responses, particularly in the activation of helper T cells. The correct identification of HLA-DR as an MHC class II antigen is vital, as it reflects the cellular interactions that facilitate adaptive immunity. In contrast, HLA-A, HLA-B, and HLA-C are all classified as MHC class I molecules, which present antigens to CD8+ cytotoxic T cells and are expressed on almost all nucleated cells. Understanding the distinction between MHC class I and class II molecules is critical in immunology as it highlights their different roles in the immune system and the types of immune cells they interact with.

MHC class II antigens are primarily involved in presenting processed antigens to CD4+ T cells, which play a crucial role in the immune response. Among the options listed, HLA-DR is classified as an MHC class II molecule.

HLA-DR is expressed on professional antigen-presenting cells, such as dendritic cells, macrophages, and B cells. These molecules are essential for initiating and regulating immune responses, particularly in the activation of helper T cells. The correct identification of HLA-DR as an MHC class II antigen is vital, as it reflects the cellular interactions that facilitate adaptive immunity.

In contrast, HLA-A, HLA-B, and HLA-C are all classified as MHC class I molecules, which present antigens to CD8+ cytotoxic T cells and are expressed on almost all nucleated cells. Understanding the distinction between MHC class I and class II molecules is critical in immunology as it highlights their different roles in the immune system and the types of immune cells they interact with.