The interleukin-12 (IL-12) family consists of four heterodimeric cytokines: IL-12, IL-23, IL-27, and IL-35. These cytokines share structural features and molecular partners but have distinct biological functions. IL-12 and IL-23 are pro-inflammatory, promoting Th1 and Th17 cell development, while IL-27 and IL-35 are immunoregulatory, suppressing immune responses. IL-35 is produced by regulatory T cells and plays a key role in inducing regulatory T cell populations. The family's unique structure allows for diverse signaling pathways, with different receptor combinations and STAT activation leading to varied functional outcomes. The IL-12 family's complexity presents challenges in therapeutic targeting, as cytokines can signal through shared receptors and chains, leading to competition and cross-talk. Understanding these interactions is crucial for developing effective therapies, as the family's unique properties influence immune responses and disease outcomes. Future research aims to clarify the mechanisms of cytokine signaling, receptor interactions, and the therapeutic potential of targeting this family.The interleukin-12 (IL-12) family consists of four heterodimeric cytokines: IL-12, IL-23, IL-27, and IL-35. These cytokines share structural features and molecular partners but have distinct biological functions. IL-12 and IL-23 are pro-inflammatory, promoting Th1 and Th17 cell development, while IL-27 and IL-35 are immunoregulatory, suppressing immune responses. IL-35 is produced by regulatory T cells and plays a key role in inducing regulatory T cell populations. The family's unique structure allows for diverse signaling pathways, with different receptor combinations and STAT activation leading to varied functional outcomes. The IL-12 family's complexity presents challenges in therapeutic targeting, as cytokines can signal through shared receptors and chains, leading to competition and cross-talk. Understanding these interactions is crucial for developing effective therapies, as the family's unique properties influence immune responses and disease outcomes. Future research aims to clarify the mechanisms of cytokine signaling, receptor interactions, and the therapeutic potential of targeting this family.