Helper T cells, also known as T_H cells, play a crucial role in the immune system by activating other immune cells, particularly macrophages. Initially, naive or inactive helper T cells become activated when they encounter dendritic cells that present antigens on MHC class II molecules. Unlike cytotoxic T cells, which induce apoptosis in infected cells, helper T cells primarily function by producing cytokines—signaling molecules that enhance the immune response.

Macrophages are essential immune cells that continuously engulf, degrade, and process pathogens. They can also present these pathogens as antigens on their own MHC class II molecules. When effector helper T cells bind to these antigens, they become activated and release cytokines that further stimulate macrophages. This interaction significantly boosts the macrophages' immune capabilities, enabling them to produce more lysosomes—organelles that aid in the destruction of pathogens—and increase the production of antimicrobial substances that effectively eliminate invaders.

The activation process can be visualized as follows: an unactivated macrophage engulfs a pathogen, processes it, and presents the resulting antigens on its surface via MHC class II molecules. When a helper T cell recognizes these antigens, it releases cytokines that activate the macrophage. This activation enhances the macrophage's ability to destroy pathogens, resulting in a more robust immune response.

In summary, helper T cells are vital for enhancing the immune response by activating macrophages and other immune cells through cytokine signaling. This collaboration improves the overall effectiveness of the immune system in combating infections.