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How do helper T cells activate other immune cells?

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Helper T cells act as essential mediators of the immune system by producing cytokines—specialized chemical messengers—that activate other immune cells.12

Once activated themselves, helper T cells stimulate other cells through the following mechanisms:

Cytokine Secretion: Helper T cells release specific cytokines that interact with other immune cells to trigger their activity. For example, IL-2 allows cytotoxic T cells that recognize the same antigen to multiply.12
Subpopulation Specialization: Helper T cells are divided into two main groups based on the cytokines they produce:12
- T_H1 cells: Primarily secrete cytokines like gamma interferon to stimulate cell-mediated responses, including the activation of macrophages and cytotoxic T cells.12
- T_H2 cells: Primarily synthesize interleukins (such as IL-4 and IL-5) to assist in stimulating B cells to produce antibodies.12
Direct Interaction: After a helper T cell is activated by an antigen, it can directly interact with and activate B cells that have encountered the same antigen, providing additional stimulation through secreted cytokines.1