MHC Class II molecules are proteins found on the surface of certain immune cells, such as B cells, dendritic cells, and macrophages. They play a crucial role in the immune system by presenting antigens, which are pieces of pathogens, to CD4+ T cells. This interaction helps activate T cells, leading to a coordinated immune response. These molecules are essential for the adaptive immune system, allowing the body to recognize and respond to specific infections. MHC Class II is inherited and varies among individuals, influencing how effectively their immune system can respond to different pathogens.