IL12B expression is sustained by a heterogenous population of myeloid lineages during tuberculosis

Abstract

Summary IL12B is required for resistance to Mycobacterium tuberculosis (Mtb) infection, promoting the initiation and maintenance of Mtb-specific effector responses. While this makes the IL12-pathway an attractive target for experimental tuberculosis (TB) therapies, data regarding what lineages express IL12B after infection is established are limited. This is not obvious in the lung, an organ in which both hematopoietic and non-hematopoietic lineages produce IL12p40 upon pathogen encounter. Here, we use radiation bone marrow chimeras and Yet40 reporter mice to determine what lineages produce IL12p40 during experimental TB. We observed that hematopoietic IL12p40-production was sufficient to control Mtb, with no contribution by non-hematopoietic lineages. Furthermore, rather than being produced by a single subset, IL12p40 was produced by cells that were heterogenous in their size, granularity, autofluorescence and expression of CD11c, CD11b and CD8α. While depending on the timepoint and tissue examined, the surface phenotype of IL12p40-producers most closely resembled macrophages based on previous surveys of lung myeloid lineages. Importantly, depletion of CDllchi cells during infection had no affect on lung IL12p40-concentrations. Collectively, our data demonstrate that IL12p40 production is sustained by a heterogenous population of myeloid lineages during experimental TB, and that redundant mechanisms of IL12p40-production exist when CD11chi lineages are absent.

Dietary Vitamin D3 Suppresses Pulmonary Immunopathology Associated with Late-Stage Tuberculosis in C3HeB/FeJ Mice

“…Instead, we found the Mtb growth characteristics in C3HeB/FeJ mice to resemble those historically observed in C57BL/6 mice (52). Nevertheless, the immunopathology we observed in C3HeB/FeJ mice was more severe than any we have ever seen in C57BL/6 mice (5, 6). Specifically, we observed necrotic areas in H37Rv-infected VitD LO mice during late stage TB that contained abundant AFB.…”

“…Two days later, culture supernatants were collected and used for ELISA measurements of both IL12/IL23p40 and IFNγ; macrophages and DCs are the principal sources of IL12/IL23p40 during experimental tuberculosis (6), while αβ T cells, NK cells, and neutrophils are the sources of IFNγ (5). The results of these recall experiments are shown in Fig 2E–F, and demonstrate that VitD LO splenocytes secreted significantly higher levels of IL12/IL23p40 and IFNγ on post-infection day 62 relative to VitD HI mice.…”

“…vdr +/+ and vdr −/− progeny were used to generate radiation bone marrow chimeras per our reported protocols, the percent reconstitution being ≥94% (5, 6). Mice were allowed 10 weeks to reconstitute prior to their use.…”

“…Mice were aerosol infected with virulent Mtb H37Rv per our reported protocols (5, 6). For bacterial load determinations, lungs and ½ spleen were removed and individually homogenized in normal sterile saline; serial dilutions of each homogenate were then plated on 7H11 and colonies counted after ≥ 2 weeks incubation at 37°C and 5% CO 2 .…”

“…In experimental TB there is a delay in Ag-specific T cell activation (4), allowing for dissemination of Mtb to extrapulmonary sites. Phagocyte production of IL12 is essential for activation of T cells and their subsequent production of IFNγ and TNFα (5, 6), which are the two major T H 1 cytokines that promote macrophage killing of intracellular Mtb (1). The necessity of IFNγ during infection is highlighted by the observation that T cells incapable of IFNγ-production are unable to control Mtb burdens (5, 7).…”