Which type of immune cells present antigens to CD4+ T cells?

• A. MHC Class I cells
• B. MHC Class II cells
• C. Plasma cells
• D. Natural killer cells

Answer: (B)

MHC Class II cells are specialized in presenting antigens to CD4+ T cells, which are a subset of T lymphocytes that play a crucial role in the immune response. The key function of MHC Class II molecules is to display processed exogenous antigens—those that have been engulfed and internally processed by antigen-presenting cells, such as B cells, macrophages, and dendritic cells.

When these antigen-presenting cells express MHC Class II molecules on their surface, they bind to the CD4+ T cell receptors, which is essential for initiating a robust immune response. This interaction not only helps to activate the CD4+ T cells but also aids in their differentiation into various helper T cell subtypes that orchestrate and enhance other elements of the immune system, including B cell activation and coordination of the attack against pathogens.

Understanding the role of MHC Class II in this context is fundamental because it highlights the intricacies of antigen presentation and how immune cells communicate to mount an effective defense against infections.