Splenic red pulp macrophages produce type I interferons as early sentinels of malaria infection but are dispensable for control.

Type I interferons (T1IFNs) are among the earliest cytokines produced during infections due to their direct regulation by innate immune signaling pathways. Reports have suggested that T1IFNs are produced during malaria infection, but little is known about the in vivo cellular origins of T1IFNs or their role in protection. We have found that in addition to plasmacytoid dendritic cells, splenic red pulp macrophages (RPMs) can generate significant quantities of T1IFNs in response to P. chabaudi infection in a TLR9-, MYD88-, and IRF7-dependent manner. Furthermore, T1IFNs regulate expression of interferon-stimulated genes redundantly with Interferon-gamma (IFNG), resulting in redundancy for resistance to experimental malaria infection. Despite their role in sensing and promoting immune responses to infection, we observe that RPMs are dispensable for control of parasitemia. Our results reveal that RPMs are early sentinels of malaria infection, but that effector mechanisms previously attributed to RPMs are not essential for control.