γδ T cell-derived IL-4 initiates CD8<sup>+</sup> T cell immunity.

Abstract

Dendritic cells (DCs) are pivotal for initiating adaptive immunity, a process triggered by the activation of DCs via pathogen products or damage. Immunization with sporozoites from Plasmodium leads to CD8⁺ T cell priming in a response initiated by collaboration between conventional type 1 DCs (cDC1s) and γδ T cells. Here we show that Vγ1⁺ γδ T cells have an initiating role by directly supplying interleukin-4 (IL-4). IL-4 and interferon-γ (IFNγ) synergize with CD4⁺ T cell-derived CD40L to induce IL-12 production by cDC1. Both IL-12 and IL-4 then directly signal responding CD8⁺ T cells and drive enhanced IL-12 receptor expression and expansion. This study shows how Vγ1⁺ γδ T cells can initiate CD8⁺ T cell immunity to Plasmodium and that responses to some pathogens require help from innate-like T cells to pass an initiation threshold and further amplify the response in a process underscored by IL-4 production.