What molecules are produced by T helper cells that function to coordinate specific and nonspecific defenses and stimulate cell-mediated and antibody-mediated immunities?

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T helper cells release signaling proteins called cytokines. These molecules act as messengers that tell other immune cells what to do, coordinating both the innate (nonspecific) and adaptive (specific) defenses. Cytokines from helper cells stimulate cytotoxic T cells to attack infected targets and help B cells mature and undergo class switching to produce different antibody isotypes, thereby enabling antibody-mediated immunity. They also activate macrophages and recruit other immune cells, linking cell-mediated and humoral responses with innate defenses.

Cytokines are signaling proteins, not enzymes (which catalyze reactions), not antibodies (produced by B cells to target pathogens directly), and not hormones in the classic endocrine sense (though they can have hormone-like effects, they are produced by immune cells to regulate immune activity).