Autophagy is a cell biological pathway affecting immune responses. In vitro, autophagy acts as a cell-autonomous defense against Mycobacterium tuberculosis, but its role in vivo is unknown. Here we show that autophagy plays a dual role against tuberculosis: antibacterial and anti-inflammatory. M. tuberculosis infection of Atg5 fl/fl LysM-Cre + mice relative to autophagy-proficient littermates resulted in increased bacillary burden and excessive pulmonary inflammation characterized by neutrophil infiltration and IL-17 response with increased IL-1α levels. Macrophages from uninfected Atg5 fl/fl LysM-Cre + mice displayed a cell-autonomous IL-1α hypersecretion phenotype, whereas T cells showed propensity toward IL-17 polarization during nonspecific activation or upon restimulation with mycobacterial antigens. Thus, autophagy acts in vivo by suppressing both M. tuberculosis growth and damaging inflammation.utophagy is a fundamental cell biological process (1) with impact on aging, development, cancer, neurodegeneration, myodegeneration, metabolic disorders (2), idiopathic inflammatory diseases, and infection and immunity (3). Much of the physiological effects of autophagy are the result of degradative activities of autophagy (1), although biogenesis and secretory roles (4-6) of autophagy are beginning to be recognized (7). The execution of autophagy depends on factors collectively termed "Atg proteins," such as Atg5 (1) and Beclin 1 (Atg6) (8), whereas regulation of autophagy responds to various inputs via mammalian target of rapamycin (mTOR), including the presence of microbes (9), the TAB2/3-TAK1-IKK signaling axis (10), and processes downstream of pattern-recognition receptors and immune cytokine activation (3,(11)(12)(13).In the context of its immunological functions, autophagy acts in four principal ways (14). (i) Autophagy cooperates with conventional pattern-recognition receptors (PRRs), such as Toll-like receptors, RIG-I-like receptors (RLRs), and NOD-like receptors, and acts as both a regulator (11,12,15,16) and an effector of PRR signaling (17-19). (ii) Autophagy affects the presentation of cytosolic antigens in the context of MHC II molecules (20) in T-cell development, differentiation, polarization, and homeostasis (21,22). (iii) Most recently, autophagy has been shown to contribute to both the negative (6,7,(23)(24)(25) and positive (6, 7) regulation of unconventional secretion of the leaderless cytosolic proteins known as "alarmins," such as IL-1β and HMGB1. (iv) Autophagy can capture and eliminate intracellular microbes, including Mycobacterium tuberculosis (17, 26-29), which was one of the first two bacterial species (26, 30) to be recognized as targets for autophagic removal. This activity recently has been shown to depend on the recognition and capture of microbes by adaptors that represent a specialized subset of PRRs termed "sequestosome-like receptors" (SLRs) (31).M. tuberculosis is one of the first microbes recognized as being subject to elimination by immunological autophagy by murine and human...

Summary Background Autophagy is a fundamental cell biological process whereby eukaryotic cells form membranes in the cytoplasm to sequester diverse intracellular targets. Although significant progress has been made in understanding the origins of autophagosomal organelles, the source of lipids that support autophagic membrane formation remain an important open question. Results Here we show that lipid droplets as cellular stores of neutral lipids including triglycerides contribute to autophagic initiation. Lipid droplets, as previously shown, were consumed upon induction of autophagy by starvation. However, inhibition of autophagic maturation by blocking acidification or using dominant negative Atg4C74A that prohibits autophagosomal closure, did not prevent disappearance of lipid droplets. Thus, lipid droplets continued to be utilized upon induction of autophagy but not as autophagic substrates in a process referred to as lipophagy. We considered an alternative model whereby lipid droplets were consumed not as a part of lipophagy but as a potential contributing source to the biogenesis of lipid precursors for nascent autophagosomes. We carried out a screen for a potential link between triglyceride mobilization and autophagy, and identified a neutral lipase, PNPLA5, as being required for efficient autophagy. PNPLA5, which localized to lipid droplets, was needed for optimal initiation of autophagy. PNPLA5 was required for autophagy of diverse substrates including degradation of autophagic adaptors, bulk proteolysis, mitochondrial quantity control, and microbial clearance. Conclusions Lipid droplets contribute to autophagic capacity by enhancing it in a process dependent on PNPLA5. Thus, neutral lipid stores are mobilized during autophagy to support autophagic membrane formation.

Interleukin-15 (IL-15 IntroductionThe generation and maintenance of memory CD8 T cells is regulated by multiple mechanisms that involve both early programming of memory T-cell precursors as well as a continuous supply of external signals. 1,2 Whereas the events and signals that program memory precursors are not well understood, interleukin-15 (IL-15) has clearly been shown to drive the generation and maintenance of memory CD8 T cells. 3,4 The recent evidence that IL-15 is delivered through the mechanism of transpresentation via IL-15R␣ by cell-cell contact 5 opens up many questions in the field of memory CD8 T-cell homeostasis, the foremost being the identity of the cell transpresenting IL-15 to memory CD8 T cells.To better understand how IL-15 transpresentation is regulated, the identity of the cell type mediating IL-15 transpresentation must be known. Studies attempting to address this have found that either parenchymal or hematopoietic cells mediate transpresentation, depending on the responding lymphocyte. 6,7 This finding is seminal as it shows that cells can be in an IL-15R␣ ϩ environment and remain ignorant to IL-15. Considering that IL-15R␣ is ubiquitously expressed, it is surprising that the responding cell has such strict requirements for a specific cell to transpresent IL-15. 8 In contrast to IL-15R␣ expression, IL-15 protein is not believed to be expressed by many IL-15R␣-expressing cells (ie, T cells); however, expression of IL-15 has been difficult to determine as reagents detecting IL-15 protein have been limited. As such, multiple studies using functional readouts have found that coexpression of IL-15 and IL-15R␣ is integral for a cell to transpresent IL-15. [9][10][11] These observations emphasize that the identity of an IL-15 transpresenting cell may not simply be implied by the expression of IL-15R␣ but rather is better determined through functional analysis.For memory CD8 T cells, in vivo studies found that IL-15R␣-expressing hematopoietic cells are the dominant cell types driving homeostatic proliferation. 7,12 The hematopoietic cells providing the IL-15 signal are RAG-1-independent, indicating that IL-15 transpresentation is not mediated by either T or B lymphocytes. 9 As DCs, monocytes, and macrophages have been shown to express IL-15R␣ protein and are capable of inducing IL-15, 13,14 these cells are potential mediators of IL-15 transpresentation. Indeed, bone marrow (BM)-derived DCs and some monocytic cell lines can transpresent IL-15 in vitro 5 ; however, whether their analogous in vivo counterparts transpresent IL-15 to CD8 T cells is not known. Since IL-15 transpresentation requires cell-cell interactions and DCs have a natural propensity for T-cell interactions, DCs are a prime candidate to transpresent IL-15 to memory CD8 T cells. Therefore, the goal of this study was to examine the contribution of DCs in transpresentation of IL-15 to CD8 T cells.In this study, we demonstrate that DCs transpresent IL-15 to CD8 T cells driving specific functions during differentiation. Although IL-15 ...

Inflammatory cytokines drive NK cell expansion in the absence of the transcription factor Nfil3, and Nfil3 is dispensable for the maintenance and function of mature NK cells.

IL-15 is a key component that regulates the development and homeostasis of NK cells and is delivered through a mechanism termed trans-presentation. During development, multiple events must proceed to generate a functional mature population of NK cells that are vital for tumor and viral immunity. Nevertheless, how IL-15 regulates these various events and more importantly what cells provide IL-15 to NK cells to drive these events is unclear. It is known dendritic cells (DC) can activate NK cells via IL-15 trans-presentation; however, the ability of DC to use IL-15 trans-presentation to promote the development and homeostatic maintenance of NK cell has not been established. In this current study, we show that IL-15 trans-presentation solely by CD11c+ cells assists the in vivo development and maintenance of NK cells. More specifically, DC-mediated IL-15 trans-presentation drove the differentiation of NK cells, which included the up-regulation of the activating and inhibitory Ly49 receptors. Although these cells did not harbor a mature CD11bhigh phenotype, they were capable of degranulating and producing IFN-γ upon stimulation similar to wild-type NK cells. In addition, DC facilitated the survival of mature NK cells via IL-15 trans-presentation in the periphery. Thus, an additional role for NK-DC interactions has been identified whereby DC support the developmental and homeostatic niche of NK cells.