The Inflammation and Innate Immunity Unit has been focusing on purchasing equipment and research supplies, successfully recruited post-doctoral fellows and advancing research projects in various areas related to host resistance against Mycobacterium tuberculosis infection as detailed below. The laboratory own BL3 laboratory is in the process fully equipped and set-up and awaits certification. The development of effective vaccines and host directed therapies (HDT) against M. tuberculosis (Mtb) infection requires a detailed understanding of the cellular basis of protective immunity. Considerable progress has been made in our understanding of protective adaptive immunity, yet relatively little is known about the contribution of innate effector cells. Particularly, the biological relevance of granulocytes like neutrophils and eosinophils is poorly understood. The innate inflammatory response is a prime target for HDT and manipulation of granulocytes could have major inflammatory and immunoregulatory implications for host resistance. Similar to neutrophils, eosinophils are phagocytic cells of the myeloid lineage that are thought to play an important effector role in the innate immune response. Their lineage-specific secondary granules contain cytotoxic cationic granular proteins (ECP, EDN, MBP and EPO) that have been shown to exhibit anti-microbial activity and cause tissue damage. Preformed cytokines contained in these same granules include inflammatory cytokines like TNF-, IL-1, IL-6 and IL-8 and pro-fibrogenic cytokines that can stimulate fibroblast proliferation, fibrotic and wound healing responses. In addition, lipid bodies, which form in response to eosinophil activation, contain a wide variety of leukotrienes, prostaglandins and reactive oxygen species that can contribute to these processes. More recently, eosinophils have been shown to play an important role in immunoregulation and homeostatic functions, including maintenance of long-lived plasma cells in the bone marrow and alternatively activated macrophages in adipose tissue. Eosinophils and their biological functions of have been studied primarily in the context of type 2 immunity, including parasitic helminth and pulmonary fungal infection, allergies and asthma. The role of eosinophils during bacterial infection remains largely unexplored. Indeed, eosinophils have been shown to exhibit bactericidal activities in response to E. coli and after P. Aeruginosa infection in vivo. There have also been reports of eosinophilic infiltration in BALF after Mtb infection in Guinea pigs and patients. However, a comprehensive study on the role of eosinophils during Mtb infection is lacking, both in animal models as well human clinical studies. Another barrier to our understanding of eosinophils in host resistance to TB is a paucity of data from the mouse model of Mtb infection. There are likely two major contributing factors to be considered for this: 1) Mtb infection primarily causes a type I immune response, and eosinophils are rare in numbers compared to neutrophils in the lungs of Mtb infected mice (KDMB unpublished data) and 2) the pathology of Mtb infected mouse lungs and human lungs is vastly different. Eosinophils were found to be enriched in areas of tissue remodeling and fibrosis in TB resected lungs from patients (KDMB unpublished data). While fibrotic responses are often seen in TB patients they are not considered a feature in the mouse model of Mtb infection. Therefore, we are currently re-evaluating the role of eosinophils in the mouse model of aerosol infection, in non-human primates infected with Mtb (in collaboration with Dan Barber) and in humans (in collaboration with Amy Klion, Ka-Wing Wong and Robert Wilkinson). In a previous collaboration with the Sher laboratory, we have characterized two major innate pathways, IL-1 and type I interferons, respectively, that play pivotal roles in governing host resistance versus disease in the murine model of Mtb infection by intersecting the eicosanoid lipid network. In particular, we uncovered that IL-1 can in turn counter-regulate type I IFN driven detrimental responses during Mtb infection. In murine and human macrophages IL-1 and IL-1 potently inhibit type I IFN induction at both the mRNA and protein level and similarly IFN mRNA and protein levels are upregulated in the lungs of Mtb infected Il1r1-/- deficient mice. This inhibition is of functional importance because mice doubly deficient in Il1r1,Ifnar1-/- are partially protected while Il1r1-/- singly deficient animals succumb rapidly to Mtb aerosol challenge. Moreover, when IL-1 is present in type I IFN treated cultures, it even suppresses the pro-bacterial effects downstream of IFN that lead to increased bacterial replication. Interestingly, IL-1 induced PGE2 is also able to potently inhibit type I IFNs in a dose dependent manner. Targeting PGE2 during Mtb infection, either via direct administration or its enhancement by 5 lipoxygenase (5-LO) blockade with Zileuton, reversed type I IFN driven mortality. These data highlighted and provided proof-of-concept that the cross-talk of IL-1 and type I IFN provides a valuable target for host-directed therapies of Mtb and plays a major role during infection in mice. However, the mechanisms how IL-1 and type I IFNs modulates bacterial replication and spread are unknown and we are currently investigating how diverse cell death modalities contribute to IL-1 mediated protection against Mtb. In addition, we are investigating the requirement for IL-1R1 expression on a variety of cell types, including macrophages, neutrophils and dendritic cells for bacterial control and protective function in pulmonary Mtb disease. In fact, myeloid-cell-intrinsic versus extrinsic requirements for IL-1R1 to control Mtb infection in mice have not been directly addressed. In this context, we have found through utilization of single cell analysis of infected cells, competitive mixed bone marrow chimeras and IL-1R1 conditional mutant mice, that IL-1R1 expression by pulmonary phagocytes is uncoupled from their ability to control intracellular Mtb growth. Importantly, IL-1R1-dependent control was provided to infected cells in trans by both non-hematopoietic and hematopoietic cells. Thus, IL-1R1-mediated host resistance to Mtb infection does not involve mechanisms of cell-autonomous anti-microbicidal effector functions in phagocytes but requires the cooperation between infected cells and other cells of hematopoietic or non-hematopoietic origin to promote bacterial containment and control of infection.
