Enriched Dietary Saturated Fatty Acids Induce Trained Immunity via Ceramide Production that Enhances Severity of Endotoxemia and clearance of infection

Trained immunity is an innate immune memory response that is induced by a primary inflammatory stimulus that sensitizes monocytes and macrophages to a secondary pathogenic challenge, reprogramming the host response to infection and inflammatory disease. Dietary fatty acids can act as inflammatory stimuli, but it is unknown if they can act as the primary stimuli to induce trained immunity. Here we find mice fed a diet enriched exclusively in saturated fatty acids (ketogenic diet; KD) confer a hyper-inflammatory response to systemic lipopolysaccharide (LPS) and increased mortality, independent of diet-induced microbiome and hyperglycemia. We find KD alters the composition of the hematopoietic stem cell compartment and enhances the response of bone marrow macrophages, monocytes, and splenocytes to secondary LPS challenge. Lipidomics identified enhanced free palmitic acid (PA) and PA-associated lipids in KD-fed mice serum. We found pre-treatment with physiologically relevant concentrations of PA induces a hyper-inflammatory response to LPS in macrophages, and this was dependent on the synthesis of ceramide. In vivo, we found systemic PA confers enhanced inflammation and mortality in response to systemic LPS, and this phenotype was not reversible for up to 7 days post-PA-exposure. Conversely, we find PA exposure enhanced clearance of Candida albicans in Rag1-/- mice. Lastly, we show that oleic acid, which depletes intracellular ceramide, reverses PA-induced hyper-inflammation in macrophages and enhanced mortality in response to LPS. These implicate enriched dietary SFAs, and specifically PA, in the induction of long-lived innate immune memory and highlight the plasticity of this innate immune reprogramming by dietary constituents

Blimp-1-Dependent Plasma Cell Differentiation Is Required for Efficient Maintenance of Murine Gammaherpesvirus Latency and Antiviral Antibody Responses▿

Recent evidence from the study of Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus supports a model in which terminal differentiation of B cells to plasma cells leads to virus reactivation. Here we address the role of Blimp-1, the master transcriptional regulator of plasma cell differentiation, in murine gammaherpesvirus 68 (MHV68) latency and reactivation. Blimp-1 expression in infected cells was dispensable for acute virus replication in the lung following intranasal inoculation and in the spleen following intraperitoneal inoculation with MHV68. However, we observed a role for Blimp-1 in both the establishment of latency and reactivation from latency in vivo. Additionally, plasma cell-deficient mice also exhibited a significant defect in the establishment of latency in the spleen, as well as reactivation from latency, similar to mice that lacked Blimp-1 only in MHV68-infected cells. In the absence of plasma cells, MHV68 infection failed to elicit a strong germinal center response and fewer B cells in the germinal center were MHV68 infected. Notably, the absence of a functional Blimp-1 gene only in MHV68-infected cells led to a decrease in both B-cell and CD4+ T-cell responses during the establishment of latency. Finally, Blimp-1 expression in infected cells played a critical role in the maintenance of both MHV68 latency in the spleen and antibody responses to MHV68. Together, these studies support a model wherein episodic Blimp-1-mediated plasma cell differentiation leads to MHV68 reactivation, which serves to both renew the latency reservoirs and stimulate long-lived plasma cells to secrete virus-specific antibody

The role of mucosal associated invariant T cells in antimicrobial immunity

Mucosal associated invariant T (MAIT) cells are an innate-like T cell subset prevalent in humans and distributed throughout the blood and mucosal sites. Human MAIT cells are defined by the expression of the semi-invariant TCRα chain TRAV1-2/TRAJ12/20/33 and are restricted by the non-polymorphic major histocompatibility complex (MHC) class I-like molecule, MHC-related protein 1, MR1. MAIT cells are activated by small organic molecules, derived from the riboflavin biosynthesis pathway of bacteria and fungi, presented by MR1. Traditionally, MAIT cells were thought to recognize a limited number of antigens due to usage of an invariant TCRα chain and restriction by a non-polymorphic MHC molecule. However, recent studies demonstrate that the TCR repertoire of MAIT cells is more heterogeneous suggesting there is a more diverse array of MR1 antigens that MAIT cells can recognize. In response to infected cells, MAIT cells produce the pro-inflammatory cytokines IFN-γ and TNF and are cytolytic. Studies performed in MR1-deficient mice suggest that MAIT cells can provide anti-bacterial control within the first few days post-infection, as well as contribute to enhanced adaptive immunity in murine models of respiratory infections. In humans, the role of MAIT cells is unclear; however evidence points to interplay between MAIT cells and microbial infections, including Mycobacterium tuberculosis. Given that MAIT cells are pro-inflammatory, serve in early control of bacterial infections, and appear enriched at tissue sites where microbes interface and gain access to the body, we postulate that they play an important role in antimicrobial immune responses. In this review we discuss the most recent studies on the function and phenotype of MAIT cells, including their TCR diversity and antigenic repertoire, with a focus on the contribution of human MAIT cells in the immune response to microbial infection

Low doses of imatinib induce myelopoiesis and enhance host anti-microbial immunity.

Imatinib mesylate (Gleevec) inhibits Abl1, c-Kit, and related protein tyrosine kinases (PTKs) and serves as a therapeutic for chronic myelogenous leukemia and gastrointestinal stromal tumors. Imatinib also has efficacy against various pathogens, including pathogenic mycobacteria, where it decreases bacterial load in mice, albeit at doses below those used for treating cancer. We report that imatinib at such low doses unexpectedly induces differentiation of hematopoietic stem cells and progenitors in the bone marrow, augments myelopoiesis but not lymphopoiesis, and increases numbers of myeloid cells in blood and spleen. Whereas progenitor differentiation relies on partial inhibition of c-Kit by imatinib, lineage commitment depends upon inhibition of other PTKs. Thus, imatinib mimics "emergency hematopoiesis," a physiological innate immune response to infection. Increasing neutrophil numbers by adoptive transfer sufficed to reduce mycobacterial load, and imatinib reduced bacterial load of Franciscella spp., which do not utilize imatinib-sensitive PTKs for pathogenesis. Thus, potentiation of the immune response by imatinib at low doses may facilitate clearance of diverse microbial pathogens

Identification and optimisation of novel sulfonamide, selective vasopressin V1B receptor antagonists

The synthesis and preliminary structure–activity relationships (SAR) of a novel class of vasopressin V1B receptor antagonists are described. Hit compound 5, identified via high throughput screening of the corporate collection, showed good activity in a V1B binding assay (Ki 63 nM) but did not possess the lead-like physicochemical properties typically required in a hit compound. A ‘deletion approach’ on the HTS hit 5 was performed, with the focus on improvement of physicochemical properties, yielding the selective V1B antagonist 9f (Ki 190 nM), with improved druglike characteristics