Setting in motion the immune mechanisms underlying genetically determined resistance and susceptibility to infection with Leishmania major.

The murine model of infection with Leishmania major has allowed the demonstration of a causal relationship between, on the one hand, genetically determined resistance to infection and the development of a Th1 CD4+ cell response, and on the other hand, genetically determined susceptibility and Th2 cell maturation. Using this murine model of infection, the role of cytokines in directing the functional differentiation pathway of CD4+ T cell precursors, has been demonstrated in vivo. Thus, IL-12 and IFN-gamma have been shown to favour Th1 cell development and IL-4 is crucial for the differentiation of Th2 responses. Maturation of a Th2 response in susceptible BALB/c mice following infection with L. major is triggered by the IL-4 produced during the first two days after parasite inoculation. This IL-4 rapidly renders parasite specific CD4+ T cells precursors unresponsive to IL-12. A restricted population of CD4+ T cells expressing the V beta 4V alpha 8 TCR heterodimer and recognizing a single epitope on the LACK (Leishmania Activated C-Kinase) antigen of L. major is responsible for this rapid production of IL-4, instructing subsequent differentiation towards the Th2 phenotype of CD4+ T cells specific for several parasite antigens.

Plant defense against herbivory: progress in identifying synergism, redundancy, and antagonism between resistance traits.

Plants respond to herbivore attack through a complex and variable system of defense, involving different physical barriers, toxic chemicals, and recruitment of natural enemies. To fully understand the relative role of each type of defense, their synergisms, redundancies, or antagonisms between traits, a variety of methods of enquiry, commonly used in plant physiology and ecology, have been employed. By overexpressing or silencing genes of interest, it is possible to understand the specific role of a particular defensive molecule or mode of action. We argue, however, that these types of experiments alone are not enough to holistically understand the physiological as well as ecological role of plant defenses. We thus advocate for the use of a combination of methods, including genetic modification, quantitative genetics, and phylogenetically controlled comparative studies.

The inflammasomes: guardians of the body.

The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1beta and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

Structure and function of a "yellow" protein from saliva of the sand fly Lutzomyia longipalpis that confers protective immunity against Leishmania major infection.

LJM11, an abundant salivary protein from the sand fly Lutzomyia longipalpis, belongs to the insect "yellow" family of proteins. In this study, we immunized mice with 17 plasmids encoding L. longiplapis salivary proteins and demonstrated that LJM11 confers protective immunity against Leishmania major infection. This protection correlates with a strong induction of a delayed type hypersensitivity (DTH) response following exposure to L. longipalpis saliva. Additionally, splenocytes of exposed mice produce IFN-γ upon stimulation with LJM11, demonstrating the systemic induction of Th1 immunity by this protein. In contrast to LJM11, LJM111, another yellow protein from L. longipalpis saliva, does not produce a DTH response in these mice, suggesting that structural or functional features specific to LJM11 are important for the induction of a robust DTH response. To examine these features, we used calorimetric analysis to probe a possible ligand binding function for the salivary yellow proteins. LJM11, LJM111, and LJM17 all acted as high affinity binders of prohemostatic and proinflammatory biogenic amines, particularly serotonin, catecholamines, and histamine. We also determined the crystal structure of LJM11, revealing a six-bladed β-propeller fold with a single ligand binding pocket located in the central part of the propeller structure on one face of the molecule. A hypothetical model of LJM11 suggests a positive electrostatic potential on the face containing entry to the ligand binding pocket, whereas LJM111 is negative to neutral over its entire surface. This may be the reason for differences in antigenicity between the two proteins.

Theileria parva-transformed T cells show enhanced resistance to Fas/Fas ligand-induced apoptosis.

Lymphocyte homeostasis is regulated by mechanisms that control lymphocyte proliferation and apoptosis. Activation-induced cell death is mediated by the expression of death ligands and receptors, which, when triggered, activate an apoptotic cascade. Bovine T cells transformed by the intracellular parasite Theileria parva proliferate in an uncontrolled manner and undergo clonal expansion. They constitutively express the death receptor Fas and its ligand, FasL but do not undergo apoptosis. Upon elimination of the parasite from the host cell by treatment with a theilericidal drug, cells become increasingly sensitive to Fas/FasL-induced apoptosis. In normal T cells, the sensitivity to death receptor killing is regulated by specific inhibitor proteins. We found that anti-apoptotic proteins such as cellular (c)-FLIP, which functions as a catalytically inactive form of caspase-8, and X-chromosome-linked inhibitor of apoptosis protein (IAP) as well as c-IAP, which can block downstream executioner caspases, are constitutively expressed in T. parva-transformed T cells. Expression of these proteins is rapidly down-regulated upon parasite elimination. Antiapoptotic proteins of the Bcl-2 family such as Bcl-2 and Bcl-x(L) are also expressed but, in contrast to c-FLIP, c-IAP, and X-chromosome-linked IAP, do not appear to be tightly regulated by the presence of the parasite. Finally, we show that, in contrast to the situation in tumor cells, the phosphoinositide 3-kinase/Akt pathway is not essential for c-FLIP expression. Our findings indicate that by inducing the expression of antiapoptotic proteins, T. parva allows the host cell to escape destruction by homeostatic mechanisms that would normally be activated to limit the continuous expansion of a T cell population.

Type I interferons protect T cells against NK cell attack mediated by the activating receptor NCR1.

Direct type I interferon (IFN) signaling on T cells is necessary for the proper expansion, differentiation, and survival of responding T cells following infection with viruses prominently inducing type I IFN. The reasons for the abortive response of T cells lacking the type I IFN receptor (Ifnar1(-/-)) remain unclear. We report here that Ifnar1(-/-) T cells were highly susceptible to natural killer (NK) cell-mediated killing in a perforin-dependent manner. Depletion of NK cells prior to lymphocytic choriomeningitis virus (LCMV) infection completely restored the early expansion of Ifnar1(-/-) T cells. Ifnar1(-/-) T cells had elevated expression of natural cytotoxicity triggering receptor 1 (NCR1) ligands upon infection, rendering them targets for NCR1 mediated NK cell attack. Thus, direct sensing of type I IFNs by T cells protects them from NK cell killing by regulating the expression of NCR1 ligands, thereby revealing a mechanism by which T cells can evade the potent cytotoxic activity of NK cells.

What makes a host profitable? Parasites balance host nutritive resources against immunity.

Numerous host qualities can modulate parasite fitness, and among these, host nutritive resources and immunity are of prime importance. Indeed, parasite fitness increases with the amount of nutritive resources extracted from the host body and decreases with host immune response. To maximize fitness, parasites have therefore to balance these two host components. Yet, because host nutritive resources and immunity both increase with host body condition, it is unclear whether parasites perform better on hosts in prime, intermediate, or poor condition. We investigated blood meal size and survival of the ectoparasitic louse fly Crataerina melbae in relation to body condition and cutaneous immune response of their Alpine swift (Apus melba) nestling hosts. Louse flies took a smaller blood meal and lived a shorter period of time when feeding on nestlings that were experimentally food deprived or had their cutaneous immune response boosted with methionine. Consistent with these results, louse fly survival was the highest when feeding on nonexperimental nestlings in intermediate body condition. Our findings emphasize that although hosts in poor condition had a reduced immunocompetence, parasites may have avoided them because individuals in poor condition did not provide adequate resources. These findings highlight the fact that giving host immunocompetence primary consideration can result in a biased appraisal of host-parasite interactions.

Microcrystals as DAMPs and their role in joint inflammation.

Microcrystals associated with joint diseases, namely monosodium urate, calcium pyrophosphate and basic calcium phosphate, can be considered as 'danger signals' to the innate immune system and provoke inflammation through inflammasome-dependent as well as inflammasome-independent pathways. Direct crystal membrane interactions can also lead to cell activation. The result is the generation of IL-1β and other pro-inflammatory cytokines. The primacy of IL-1β in the case of gouty inflammation has been demonstrated by the efficacy of IL-1 inhibitors in clinical studies. These findings may be relevant to other diseases where crystal formation is found, such as OA and atherosclerosis.

Immunity to pneumococcal surface proteins in children with community-acquired pneumonia: a distinct pattern of responses to pneumococcal choline-binding protein A.

Clin Microbiol Infect ABSTRACT: The aetiological diagnosis of community-acquired pneumonia (CAP) is challenging in children, and serological markers would be useful surrogates for epidemiological studies of pneumococcal CAP. We compared the use of anti-pneumolysin (Ply) antibody alone or with four additional pneumococcal surface proteins (PSPs) (pneumococcal histidine triad D (PhtD), pneumococcal histidine triad E (PhtE), LytB, and pneumococcal choline-binding protein A (PcpA)) as serological probes in children hospitalized with CAP. Recent pneumococcal exposure (positive blood culture for Streptococcus pneumoniae, Ply(+) blood PCR finding, and PSP seroresponse) was predefined as supporting the diagnosis of presumed pneumococcal CAP (P-CAP). Twenty-three of 75 (31%) children with CAP (mean age 33.7 months) had a Ply(+) PCR finding and/or a ≥2-fold increase of antibodies. Adding seroresponses to four PSPs identified 12 additional patients (35/75, 45%), increasing the sensitivity of the diagnosis of P-CAP from 0.44 (Ply alone) to 0.94. Convalescent anti-Ply and anti-PhtD antibody titres were significantly higher in P-CAP than in non P-CAP patients (446 vs. 169 ELISA Units (EU)/mL, p 0.031, and 189 vs. 66 EU/mL, p 0.044), confirming recent exposure. Acute anti-PcpA titres were three-fold lower (71 vs. 286 EU/mL, p <0.001) in P-CAP children. Regression analyses confirmed a low level of acute PcpA antibodies as the only independent predictor (p 0.002) of P-CAP. Novel PSPs facilitate the demonstration of recent pneumococcal exposure in CAP children. Low anti-PcpA antibody titres at admission distinguished children with P-CAP from those with CAP with a non-pneumococcal origin.

Impaired natural killing of MHC class I-deficient targets by NK cells expressing a catalytically inactive form of SHP-1.

NK cell function is negatively regulated by MHC class I-specific inhibitory receptors. Transduction of the inhibitory signal involves protein tyrosine phosphatases such as SHP-1 (SH2-containing protein tyrosine phosphatase-1). To investigate the role of SHP-1 for NK cell development and function, we generated mice expressing a catalytically inactive, dominant-negative mutant of SHP-1 (dnSHP-1). In this paper we show that expression of dnSHP-1 does not affect the generation of NK cells even though MHC receptor-mediated inhibition is partially impaired. Despite this defect, these NK cells do not kill syngeneic, normal target cells. In fact dnSHP-1-expressing NK cells are hyporesponsive toward MHC-deficient target cells, suggesting that non-MHC-specific NK cell activation is significantly reduced. In contrast, these NK cells mediate Ab-dependent cell-mediated cytotoxicity and prevent the engraftment with beta2-microglobulin-deficient bone marrow cells. A similar NK cell phenotype is observed in viable motheaten (mev) mice, which show reduced SHP-1 activity due to a mutation in the Shp-1 gene. In addition, NK cells in both mouse strains show a tendency to express more inhibitory MHC-specific Ly49 receptors. Our results demonstrate the importance of SHP-1 for the generation of functional NK cells, which are able to react efficiently to the absence of MHC class I molecules from normal target cells. Therefore, SHP-1 may play an as-yet-unrecognized role in some NK cell activation pathways. Alternatively, a reduced capacity to transduce SHP-1-dependent inhibitory signals during NK cell development may be compensated by the down-modulation of NK cell triggering pathways.

Myeloid differentiation factor-88/interleukin-1 signaling controls cardiac fibrosis and heart failure progression in inflammatory dilated cardiomyopathy.

RATIONALE: The myeloid differentiation factor (MyD)88/interleukin (IL)-1 axis activates self-antigen-presenting cells and promotes autoreactive CD4(+) T-cell expansion in experimental autoimmune myocarditis, a mouse model of inflammatory heart disease. OBJECTIVE: The aim of this study was to determine the role of MyD88 and IL-1 in the progression of acute myocarditis to an end-stage heart failure. METHODS AND RESULTS: Using alpha-myosin heavy chain peptide (MyHC-alpha)-loaded, activated dendritic cells, we induced myocarditis in wild-type and MyD88(-/-) mice with similar distributions of heart-infiltrating cell subsets and comparable CD4(+) T-cell responses. Injection of complete Freund's adjuvant (CFA) or MyHC-alpha/CFA into diseased mice promoted cardiac fibrosis, induced ventricular dilation, and impaired heart function in wild-type but not in MyD88(-/-) mice. Experiments with chimeric mice confirmed the bone marrow origin of the fibroblasts replacing inflammatory infiltrates and showed that MyD88 and IL-1 receptor type I signaling on bone marrow-derived cells was critical for development of cardiac fibrosis during progression to heart failure. CONCLUSIONS: Our findings indicate a critical role of MyD88/IL-1 signaling in the bone marrow compartment in postinflammatory cardiac fibrosis and heart failure and point to novel therapeutic strategies against inflammatory cardiomyopathy.

Leishmania major induces distinct neutrophil phenotypes in mice that are resistant or susceptible to infection.

Polymorphonuclear neutrophils (PMN) are key components of the inflammatory response contributing to the development of pathogen-specific immune responses. Following infection with Leishmania major, neutrophils are recruited within hours to the site of parasite inoculation. C57BL/6 mice are resistant to infection, and BALB/c mice are susceptible to infection, developing unhealing, inflammatory lesions. In this report, we investigated the expression of cell surface integrins, TLRs, and the secretion of immunomodulatory cytokines by PMN of both strains of mice, in response to infection with L. major. The parasite was shown to induce CD49d expression in BALB/c-inflammatory PMN, and expression of CD49d remained at basal levels in C57BL/6 PMN. Equally high levels of CD11b were expressed on PMN from both strains. In response to L. major infection, the levels of TLR2, TLR7, and TLR9 mRNA were significantly higher in C57BL/6 than in BALB/c PMN. C57BL/6 PMN secreted biologically active IL-12p70 and IL-10. In contrast, L. major-infected BALB/c PMN transcribed and secreted high levels of IL-12p40 but did not secrete biologically active IL-12p70. Furthermore, IL-12p40 was shown not to associate with IL-23 p19 but formed IL-12p40 homodimers with inhibitory activity. No IL-10 was secreted by BALB/c PMN. Thus, following infection with L. major, in C57BL/6 mice, PMN could constitute one of the earliest sources of IL-12, and in BALB/c mice, secretion of IL-12p40 could contribute to impaired, early IL-12 signaling. These distinct PMN phenotypes may thus influence the development of L. major-specific immune response.

NLRC5 deficiency selectively impairs MHC class I- dependent lymphocyte killing by cytotoxic T cells.

Nucleotide-binding oligomerization domain-like receptors (NLRs) are intracellular proteins involved in innate-driven inflammatory responses. The function of the family member NLR caspase recruitment domain containing protein 5 (NLRC5) remains a matter of debate, particularly with respect to NF-κB activation, type I IFN, and MHC I expression. To address the role of NLRC5, we generated Nlrc5-deficient mice (Nlrc5(Δ/Δ)). In this article we show that these animals exhibit slightly decreased CD8(+) T cell percentages, a phenotype compatible with deregulated MHC I expression. Of interest, NLRC5 ablation only mildly affected MHC I expression on APCs and, accordingly, Nlrc5(Δ/Δ) macrophages efficiently primed CD8(+) T cells. In contrast, NLRC5 deficiency dramatically impaired basal expression of MHC I in T, NKT, and NK lymphocytes. NLRC5 was sufficient to induce MHC I expression in a human lymphoid cell line, requiring both caspase recruitment and LRR domains. Moreover, endogenous NLRC5 localized to the nucleus and occupied the proximal promoter region of H-2 genes. Consistent with downregulated MHC I expression, the elimination of Nlrc5(Δ/Δ) lymphocytes by cytotoxic T cells was markedly reduced and, in addition, we observed low NLRC5 expression in several murine and human lymphoid-derived tumor cell lines. Hence, loss of NLRC5 expression represents an advantage for evading CD8(+) T cell-mediated elimination by downmodulation of MHC I levels-a mechanism that may be exploited by transformed cells. Our data show that NLRC5 acts as a key transcriptional regulator of MHC I in lymphocytes and support an essential role for NLRs in directing not only innate but also adaptive immune responses.