What is the main role of Major Histocompatibility Complex (MHC) class II molecules in the immune response?

- The main role of MHC class II molecules is to present exogenous antigens (derived from extracellular pathogens) to CD4+ helper T cells.
- This presentation is crucial for initiating the adaptive immune response, as it activates CD4+ T cells, which in turn help coordinate antibody production and activate other immune cells.
- Unlike MHC class I, which presents endogenous antigens to CD8+ T cells, MHC class II specializes in alerting the immune system to extracellular threats.

Reference: Roitt's Essential Immunology, 13th Edition, Chapter 4