MHC Class II antigens are found only on which type of cells?

MHC Class II antigens are found only on which type of cells?

• A. All body cells
• B. B cells, dendritic cells, and macrophages
• C. T cells and memory cells
• D. Red blood cells and plasma cells

Answer: (B)

MHC Class II antigens are specifically expressed on professional antigen-presenting cells (APCs), which include B cells, dendritic cells, and macrophages. These cells play a crucial role in the immune system by presenting processed antigens to CD4+ T helper cells, facilitating a specific immune response.

The reason why only these types of cells express MHC Class II antigens is that they are responsible for the uptake, processing, and presentation of antigens derived from extracellular pathogens. This is critical for activating T cells, which then help instigate a broader immune response, including the activation of B cells for antibody production.

In contrast, other cell types such as all body cells, T cells, and red blood cells do not generally express MHC Class II molecules. T cells primarily express MHC Class I molecules for recognition of endogenous antigens, while red blood cells lack MHC molecules entirely since they do not participate in antigen presentation.