The subunits of IL-12, originating from two distinct cells, can functionally synergize to protect against pathogen dissemination in vivo

Cytokines are typically single gene products, except for the heterodimeric interleukin (IL)-12 family. The two subunits (IL-12p40 and IL-12p35) of the prototype IL-12 are known to be simultaneously co-expressed in activated myeloid cells, which secrete the fully active heterodimer to promote interferon (IFN)γ production in innate and adaptive cells. We find that chimeric mice containing mixtures of cells that can only express either IL-12p40 or IL-12p35, but not both together, generate functional IL-12. This alternate two-cell pathway requires IL-12p40 from hematopoietic cells to extracellularly associate with IL-12p35 from radiation-resistant cells. The two-cell mechanism is sufficient to propel local T cell differentiation in sites distal to the initial infection and helps control systemic dissemination of a pathogen, although not parasite burden, at the site of infection. Broadly, this suggests that early secretion of IL-12p40 monomers by sentinel cells at the infection site may help prepare distal host tissues for potential pathogen arrival. [Display omitted] •Both p35 and p40 subunits of IL-12 are required to differentiate IFNγ-producing T cells•p35 and p40 produced by two different cells can collaborate to drive T cell responses•The two-cell IL-12 activity requires hematopoietic p40 but can use stromal p35•Two-cell IL-12 activity is useful for controlling pathogen dissemination in vivo The innate cytokine IL-12 is a critical enhancer of IFNγ production. Gerber et al. show that IL-12 activity can result from two distinct cells contributing different subunits of IL-12 independently, in vivo. This collaborative, two-cell version of IL-12 could limit pathogen dissemination to tissues distant from the primary infection site.