Swine Interleukin-12/Interleukin-23 p40 (IL-12/IL-23 p40) is a cytokine subunit that plays an important role in regulating immune responses in pigs (Sus scrofa). The p40 subunit is shared by two heterodimeric cytokines, IL-12 and IL-23, where it pairs with the p35 subunit to form IL-12 and with the p19 subunit to form IL-23. These cytokines are produced primarily by activated antigen-presenting cells, including macrophages and dendritic cells, in response to microbial infection or inflammatory stimuli. Swine IL-12/IL-23 p40 contributes to activation of natural killer (NK) cells and differentiation of T helper cells toward Th1-type immune responses, promoting production of interferon-γ (IFN-γ) and enhancing cell-mediated immunity against intracellular pathogens. Through IL-23 signaling, the p40 subunit also supports maintenance and expansion of Th17 cells involved in inflammatory and host defense pathways. In pigs, IL-12/IL-23 p40 participates in immune responses against viral, bacterial, and parasitic infections and is studied in the context of important swine diseases such as porcine reproductive and respiratory syndrome virus (PRRSV), African swine fever virus (ASFV), and Salmonella infections. Due to its role in regulating cellular immunity, swine IL-12/IL-23 p40 is widely studied in veterinary immunology and translational research, including investigations of host–pathogen interactions, vaccine development, and immune responses relevant to both swine health and comparative biomedical research.