Background. Statins are cholesterol-lowering drugs, targeting HMG-CoA reductase, thereby reducing the risk of coronary disorders and hypercholesterolemia. However, they also can influence immunologic responses. Methods. Peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages (MDMs) were isolated from patients with familial hypercholesterolemia (FH) during statin therapy. After infection of cells with Mycobacterium tuberculosis, bacterial burden was determined. In vivo, mice were treated with statins before aerosol-based infection with M. tuberculosis and were monitored for disease progression. Results. PBMCs and MDMs from patients with FH receiving statin therapy were more resistant to M. tuberculosis infection, with reduced bacterial burdens, compared with those of healthy donors. Moreover, statin treatment in experimental murine M. tuberculosis infection studies increased host protection, with reduced lung burdens and improved histopathologic findings. Mechanistically, metabolic rescue experiments demonstrated that statins reduce membrane cholesterol levels, particularly by the mevalonate-isoprenoid arm of the sterol pathway. This promoted phagosomal maturation (EEA-1/Lamp-3) and autophagy (LC3-II), as shown by confocal microscopy and Western blot in macrophages. In addition, inhibitors of phagosome and autophagosome maturation reversed the beneficial effect of statins on bacterial growth. Conclusion. These results suggest that statin-mediated reduction in cholesterol levels within phagosomal membranes counteract M. tuberculosis–induced inhibition of phagosomal maturation and promote host-induced autophagy, thereby augmenting host protection against tuberculosis.

Basic leucine zipper transcription factor Batf2 is poorly described, whereas Batf and Batf3 have been shown to play essential roles in dendritic cell, T cell, and B cell development and regulation. Batf2 was drastically induced in IFN-γ–activated classical macrophages (M1) compared with unstimulated or IL-4–activated alternative macrophages (M2). Batf2 knockdown experiments from IFN-γ–activated macrophages and subsequent expression profiling demonstrated important roles for regulation of immune responses, inducing inflammatory and host-protective genes Tnf, Ccl5, and Nos2. Mycobacterium tuberculosis (Beijing strain HN878)–infected macrophages further induced Batf2 and augmented host-protective Batf2-dependent genes, particularly in M1, whose mechanism was suggested to be mediated through both TLR2 and TLR4 by LPS and heat-killed HN878 (HKTB) stimulation experiments. Irf1 binding motif was enriched in the promoters of Batf2-regulated genes. Coimmunoprecipitation study demonstrated Batf2 association with Irf1. Furthermore, Irf1 knockdown showed downregulation of IFN-γ– or LPS/HKTB-activated host-protective genes Tnf, Ccl5, Il12b, and Nos2. Conclusively, Batf2 is an activation marker gene for M1 involved in gene regulation of IFN-γ–activated classical macrophages, as well as LPS/HKTB-induced macrophage stimulation, possibly by Batf2/Irf1 gene induction. Taken together, these results underline the role of Batf2/Irf1 in inducing inflammatory responses in M. tuberculosis infection.

In BALB/c mice, susceptibility to infection with the intracellular parasite Leishmania major is driven largely by the development of T helper 2 (Th2) responses and the production of interleukin (IL)-4 and IL-13, which share a common receptor subunit, the IL-4 receptor alpha chain (IL-4Rα). While IL-4 is the main inducer of Th2 responses, paradoxically, it has been shown that exogenously administered IL-4 can promote dendritic cell (DC) IL-12 production and enhance Th1 development if given early during infection. To further investigate the relevance of biological quantities of IL-4 acting on DCs during in vivo infection, DC specific IL-4Rα deficient (CD11c^creIL-4Rα^-/lox) BALB/c mice were generated by gene targeting and site-specific recombination using the cre/loxP system under control of the cd11c locus. DNA, protein, and functional characterization showed abrogated IL-4Rα expression on dendritic cells and alveolar macrophages in CD11c^creIL-4Rα^-/lox mice. Following infection with L. major, CD11c^creIL-4Rα^-/lox mice became hypersusceptible to disease, presenting earlier and increased footpad swelling, necrosis and parasite burdens, upregulated Th2 cytokine responses and increased type 2 antibody production as well as impaired classical activation of macrophages. Hypersusceptibility in CD11c^creIL-4Rα^-/lox mice was accompanied by a striking increase in parasite burdens in peripheral organs such as the spleen, liver, and even the brain. DCs showed increased parasite loads in CD11c^creIL-4Rα^-/lox mice and reduced iNOS production. IL-4Rα-deficient DCs produced reduced IL-12 but increased IL-10 due to impaired DC instruction, with increased mRNA expression of IL-23p19 and activin A, cytokines previously implicated in promoting Th2 responses. Together, these data demonstrate that abrogation of IL-4Rα signaling on DCs is severely detrimental to the host, leading to rapid disease progression, and increased survival of parasites in infected DCs due to reduced killing effector functions. Leishmaniasis is a parasitic infection caused by protozoan parasites of Leishmania species and is transmitted by the sandfly. Disease in humans ranges from localized cutaneous lesions to disseminated visceral Leishmaniasis. Mouse models of Leishmania major infection have demonstrated that a “healing” response in C57BL/6 mice requires the secretion of protective T helper (Th) 1 cytokines, including IFN-γ, which mediates parasite killing by inducing nitric oxide production. Conversely, “non-healer” BALB/c mice are unable to control infection and develop a Th2 immune response characterized by the production of IL-4 and IL-13 cytokines. Although IL-4 is the main inducer of Th2 responses, it has been shown that IL-4 can instruct dendritic cell (DC)-derived IL-12 production and Th1 development if administered during DC activation. To further investigate the role of DCs, a DC specific IL-4Rα-deficient mouse model was established. L. major studies demonstrated hypersusceptibility to infection and strikingly increased parasite loads in peripheral organs of mice lacking IL-4Rα on DCs. Moreover, increased parasite burdens were observed in host cells, including DCs, which showed reduced killing effector functions. In summary, this study demonstrates that IL-4Rα-mediated instruction of DCs occurs in vivo and is necessary to avoid rapid progression of disease in the host.

Significance: Cutaneous leishmaniasis and schistosomiasis are neglected tropical diseases for which there are no effective vaccines and limited treatment strategies. To develop vaccine and therapeutic alternatives, a detailed understanding of host immunity is essential. We show a role for IL-4Rα–responsive B cells in host susceptibility toLeishmania majorand protection againstSchistosoma mansoniinfection through the production of early IL-4, which in turn regulates Th2 cell polarization and disease outcome in mice. These important findings highlight the significant impacts that B cell-specific IL-4Rα and IL-4 responsiveness have in the context of type 1 (L. major) and type 2 (S. mansoni) pathogens. Thus, vaccine and therapeutic development should aim to target both B and T cell immunity for optimal efficacy.