MHC class II molecules bind to _________ and trigger __________ .
a. endogenous antigens; cytotoxic T cells
b. exogenous antigens; cytotoxic T cells
c. antibodies; B cells
d. endogenous antigens; helper T cells
e. exogenous antigens; helper T cells

Verified step by step guidance

1. Understand the role of MHC class II molecules: MHC class II molecules are primarily found on antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. Their main function is to present antigens to T cells.
2. Identify the type of antigens MHC class II molecules bind: MHC class II molecules present exogenous antigens, which are antigens that originate outside the cell and are taken up by the APC through processes like phagocytosis or endocytosis.
3. Determine which T cells interact with MHC class II: MHC class II molecules present these exogenous antigens to helper T cells (CD4+ T cells), which then become activated to coordinate the immune response.
4. Recall the function triggered by this interaction: When helper T cells recognize the antigen-MHC class II complex, they become activated and help stimulate other immune cells, such as B cells and cytotoxic T cells, to respond effectively.
5. Match the correct option based on the above information: MHC class II molecules bind to exogenous antigens and trigger helper T cells.

Key Concepts

MHC Class II Molecules

MHC class II molecules are proteins found on the surface of antigen-presenting cells like macrophages, dendritic cells, and B cells. They present processed exogenous antigens, which originate outside the cell, to the immune system. This presentation is crucial for initiating specific immune responses.

Exogenous vs. Endogenous Antigens

Exogenous antigens come from outside the cell and are engulfed and processed by antigen-presenting cells, whereas endogenous antigens originate within infected or abnormal cells. MHC class II molecules present exogenous antigens, while MHC class I molecules present endogenous antigens.

Helper T Cells Activation

Helper T cells recognize antigens presented by MHC class II molecules and become activated. Once activated, they coordinate the immune response by stimulating other immune cells, such as B cells and cytotoxic T cells, to effectively combat pathogens.