IL-4Rα-dependent alternative activation of macrophages is not decisive for Mycobacterium tuberculosis pathology and bacterial burden in mice.

Classical activation of macrophages (caMph or M1) is crucial for host protection against Mycobacterium tuberculosis (Mtb) infection. Evidence suggests that IL-4/IL-13 alternatively activated macrophages (aaMph or M2) are exploited by Mtb to divert microbicidal functions of caMph. To define the functions of M2 macrophages during tuberculosis (TB), we infected mice deficient for IL-4 receptor α on macrophages (LysMcreIL-4Rα-/lox) with Mtb. We show that absence of IL-4Rα on macrophages does not play a major role during infection with Mtb H37Rv, or the clinical Beijing strain HN878. This was demonstrated by similar mortality, bacterial burden, histopathology and T cell proliferation between infected wild-type (WT) and LysMcreIL-4Rα-/lox mice. Interestingly, we observed no differences in the lung expression of inducible nitric oxide synthase (iNOS) and Arginase 1 (Arg1), well-established markers for M1/M2 macrophages among the Mtb-infected groups. Kinetic expression studies of IL-4/IL-13 activated bone marrow-derived macrophages (BMDM) infected with HN878, followed by gene set enrichment analysis, revealed that the MyD88 and IL-6, IL-10, G-CSF pathways are significantly enriched, but not the IL-4Rα driven pathway. Together, these results suggest that IL-4Rα-macrophages do not play a central role in TB disease progression.

PKCδ regulates IL-12p40/p70 production by macrophages and dendritic cells, driving a type 1 healer phenotype in cutaneous leishmaniasis.

The protein kinase C (PKC) family is involved in the regulation of many intracellular signalling pathways. Here, we report that the PKCδ isoform regulates IL-12p40/p70 production in macrophages and DC and that PKCδ deficiency in mice transforms the 129/Sv healer to a non-healer strain during cutaneous leishmaniasis. Leishmania major-infected PKCδ(-/-) 129/Sv mice developed a rapid increase in footpad swelling and parasite burden with disease progression, leading to necrosis and ulceration similar to non-healer BALB/c mice. Moreover, PKCδ(-/-) mice failed to develop delayed-type hypersensitivity responses against Leishmania antigen. PKCδ(-/-) macrophages were fully functional with normal MHC class II surface expression and GM-CSF production, recruitment to the draining lymph node and killing effector functions by NO production. In contrast, macrophages and DC produced significantly reduced IL-12p40 and IL-12p70 compared to the WT cells. Decreased IL-12 production resulted in diminished Th1 differentiation, as determined by a striking reduction in IFN-γ by antigen-specific stimulated CD4(+) T cells isolated from popliteal lymph nodes of L. major-infected PKCδ(-/-) mice, explaining the "non-healer" phenotype. We conclude from these data that PKCδ is a regulator of IL-12p40/p70 production by DC and macrophages, driving the healer phenotype during cutaneous leishmaniasis.

IL-4Ralpha-independent expression of mannose receptor and Ym1 by macrophages depends on their IL-10 responsiveness.

IL-4Ralpha-dependent responses are essential for granuloma formation and host survival during acute schistosomiasis. Previously, we demonstrated that mice deficient for macrophage-specific IL-4Ralpha (LysM(cre)Il4ra(-/lox)) developed increased hepatotoxicity and gut inflammation; whereas inflammation was restricted to the liver of mice lacking T cell-specific IL-4Ralpha expression (iLck(cre)Il4ra(-/lox)). In the study presented here we further investigated their role in liver granulomatous inflammation. Frequencies and numbers of macrophage, lymphocyte or granulocyte populations, as well as Th1/Th2 cytokine responses were similar in Schistosoma mansoni-infected LysM(cre)Il4ra(-/lox) liver granulomas, when compared to Il4ra(-/lox) control mice. In contrast, a shift to Th1 responses with high IFN-gamma and low IL-4, IL-10 and IL-13 was observed in the severely disrupted granulomas of iLck(cre)Il4ra(-/lox) and Il4ra(-/-) mice. As expected, alternative macrophage activation was reduced in both LysM(cre)Il4ra(-/lox) and iLck(cre)Il4ra(-/lox) granulomas with low arginase 1 and heightened nitric oxide synthase RNA expression in granuloma macrophages of both mouse strains. Interestingly, a discrete subpopulation of SSC(high)CD11b+I-A/I-E(high)CD204+ macrophages retained expression of mannose receptor (MMR) and Ym1 in LysM(cre)Il4ra(-/lox) but not in iLck(cre)Il4ra(-/lox) granulomas. While aaMphi were in close proximity to the parasite eggs in Il4ra(-/lox) control mice, MMR+Ym1+ macrophages in LysM(cre)Il4ra(-/lox) mice were restricted to the periphery of the granuloma, indicating that they might have different functions. In vivo IL-10 neutralisation resulted in the disappearance of MMR+Ym1+ macrophages in LysM(cre)Il4ra(-/lox) mice. Together, these results show that IL-4Ralpha-responsive T cells are essential to drive alternative macrophage activation and to control granulomatous inflammation in the liver. The data further suggest that in the absence of macrophage-specific IL-4Ralpha signalling, IL-10 is able to drive mannose receptor- and Ym1-positive macrophages, associated with control of hepatic granulomatous inflammation.

OntoDas - a tool for facilitating the construction of complex queries to the Gene Ontology.

BACKGROUND: Ontologies such as the Gene Ontology can enable the construction of complex queries over biological information in a conceptual way, however existing systems to do this are too technical. Within the biological domain there is an increasing need for software that facilitates the flexible retrieval of information. OntoDas aims to fulfil this need by allowing the definition of queries by selecting valid ontology terms. RESULTS: OntoDas is a web-based tool that uses information visualisation techniques to provide an intuitive, interactive environment for constructing ontology-based queries against the Gene Ontology Database. Both a comprehensive use case and the interface itself were designed in a participatory manner by working with biologists to ensure that the interface matches the way biologists work. OntoDas was further tested with a separate group of biologists and refined based on their suggestions. CONCLUSION: OntoDas provides a visual and intuitive means for constructing complex queries against the Gene Ontology. It was designed with the participation of biologists and compares favourably with similar tools. It is available at http://ontodas.nbn.ac.za.

The role of B-cells and IgM antibodies in parasitemia, anemia, and VSG switching in Trypanosoma brucei-infected mice.

African trypanosomes are extracellular parasitic protozoa, predominantly transmitted by the bite of the haematophagic tsetse fly. The main mechanism considered to mediate parasitemia control in a mammalian host is the continuous interaction between antibodies and the parasite surface, covered by variant-specific surface glycoproteins. Early experimental studies have shown that B-cell responses can be strongly protective but are limited by their VSG-specificity. We have used B-cell (microMT) and IgM-deficient (IgM(-/-)) mice to investigate the role of B-cells and IgM antibodies in parasitemia control and the in vivo induction of trypanosomiasis-associated anemia. These infection studies revealed that that the initial setting of peak levels of parasitemia in Trypanosoma brucei-infected microMT and IgM(-/-) mice occurred independent of the presence of B-cells. However, B-cells helped to periodically reduce circulating parasites levels and were required for long term survival, while IgM antibodies played only a limited role in this process. Infection-associated anemia, hypothesized to be mediated by B-cell responses, was induced during infection in microMT mice as well as in IgM(-/-) mice, and as such occurred independently from the infection-induced host antibody response. Antigenic variation, the main immune evasion mechanism of African trypanosomes, occurred independently from host antibody responses against the parasite's ever-changing antigenic glycoprotein coat. Collectively, these results demonstrated that in murine experimental T. brucei trypanosomiasis, B-cells were crucial for periodic peak parasitemia clearance, whereas parasite-induced IgM antibodies played only a limited role in the outcome of the infection.

Host-directed drug targeting of factors hijacked by pathogens.

The current paradigm for managing infectious diseases has targeted unique processes or enzymes within pathogens. A serious disadvantage of this pathogen-directed drug targeting strategy has been the development of microbial drug resistance and consequent resurgence of once-contained infectious diseases. A new drug discovery paradigm has therefore emerged focusing on identifying and targeting host factors essential for pathogen entry, survival, and replication. Innovative strategies combining genome-wide computational biology, genomics, proteomics, and traditional forward and reverse genetics have identified host-pathogen interactions and host functions critical for the establishment of infection. Chemogenomics and chemical genetics have allowed rapid identification of new and existing licensed drugs with antimicrobial activity. Although most host-directed drug targeting studies have focused on viral infections, they have provided a proof of concept for similar approaches to bacterial and parasite infections. Future therapies may combine conventional targeting of microbial virulence factors, together with host-directed drug therapy and augmentation of protective host factors, to efficiently eliminate the invading pathogen.

Protein kinase C delta is essential for optimal macrophage-mediated phagosomal containment of Listeria monocytogenes.

Activation of macrophages and subsequent "killing" effector functions against infectious pathogens are essential for the establishment of protective immunity. NF-IL6 is a transcription factor downstream of IFN-gamma and TNF in the macrophage activation pathway required for bacterial killing. Comparison of microarray expression profiles of Listeria monocytogenes (LM)-infected macrophages from WT and NF-IL6-deficient mice enabled us to identify candidate genes downstream of NF-IL6 involved in the unknown pathways of LM killing independent of reactive oxygen intermediates and reactive nitrogen intermediates. One differentially expressed gene, PKCdelta, had higher mRNA levels in the LM-infected NF-IL6-deficient macrophages as compared with WT. To define the role of PKCdelta during listeriosis, we infected PKCdelta-deficient mice with LM. PKCdelta-deficient mice were highly susceptible to LM infection with increased bacterial burden and enhanced histopathology despite enhanced NF-IL6 mRNA expression. Subsequent studies in PKCdelta-deficient macrophages demonstrated that, despite elevated levels of proinflammatory cytokines and NO production, increased escape of LM from the phagosome into the cytoplasm and uncontrolled bacterial growth occurred. Taken together these data identified PKCdelta as a critical factor for confinement of LM within macrophage phagosomes.

TH1-dominant granulomatous pathology does not inhibit fibrosis or cause lethality during murine schistosomiasis.

Schistosoma mansoni egg-induced inflammation is accompanied by TH2 cell polarization and development of fibrotic granulomas in host tissue. The interleukin (IL)-4 receptor alpha (IL-4Ralpha), which mediates IL-4 and IL-13 signaling, is essential for granulomatous pathology through a putative CD4+ T-cell-dependent mechanism. In this study, we asked whether CD4+ T-cell-specific IL-4Ralpha-deficient mice (Lck(Cre)IL-4Ralpha(-/lox)) developed granulomas and egg-driven collagen production. Although eosinophilia and goblet cell hyperplasia were impaired in Lck(Cre)IL-4Ralpha(-/lox) mice, there was no reduction in size or collagen content of lung and liver granulomas. The lack of CD4+ T-cell IL-4Ralpha expression caused significant increases in interferon-gamma-producing cells, inducible nitric-oxide synthetase production, and hepatic damage, compared with similarly infected wild-type mice. Interestingly, this TH1-associated liver injury did not lead to premature mortality in this strain. Instead, lower levels of serum endotoxin in Lck(Cre)IL-4Ralpha(-/lox) mice suggest that intestinal barrier function may be the dominant factor for survival during natural infection.

Impairment of alternative macrophage activation delays cutaneous leishmaniasis in nonhealing BALB/c mice.

Expressed on various cell types, the IL-4Ralpha is a component of both receptors for IL-4 and IL-13. Susceptibility of BALB/c mice to Leishmania major is believed to be dependent on the development of IL-4- and IL-13-producing Th2 cells, while IFN-gamma secretion by Th1 cells is related to resistance. Despite a sustained development of Th2 cells, IL-4Ralpha-deficient BALB/c mice are able to control acute cutaneous leishmaniasis, suggesting that IL-4Ralpha-bearing cells other than Th2 cells contribute to susceptibility. To analyze the contribution of the IL-4Ralpha on macrophages, recently generated macrophage/neutrophil-specific IL-4Ralpha-deficient mice on a susceptible BALB/c genetic background were infected with L. major. Strikingly, macrophage/neutrophil-specific IL-4Ralpha-deficient mice showed a significantly delayed disease progression with normal Th2 and type 2 Ab responses but improved macrophage leishmanicidal effector functions and reduced arginase activity. Together, these results suggest that alternative macrophage activation contributes to susceptibility in cutaneous leishmaniasis.

Alternative macrophage activation is essential for survival during schistosomiasis and downmodulates T helper 1 responses and immunopathology.

Macrophage/neutrophil-specific IL-4 receptor alpha-deficient mice (LysM(Cre)IL-4Ralpha(-/flox)) were generated to understand the role of IL-4/IL-13 responsive myeloid cells during Type 2 immune responses. LysM(Cre)IL-4Ralpha(-/flox) mice developed protective immunity against Nippostrongylus brasiliensis accompanied by T(H)2 development and goblet cell hyperplasia. In contrast, LysM(Cre)IL-4Ralpha(-/flox) mice were extremely susceptible to Schistosoma mansoni infection with 100% mortality during acute infection. Mortality was not dependent on neutrophils and occurred in the presence of T(H)2/Type 2 responses, granuloma formation, and egg-induced fibrosis. Death was associated with increased T(H)1 cytokines, hepatic and intestinal histopathology, increased NOS-2 activity, impaired egg expulsion, and sepsis. IL-10 was not able to compensate for the absence of IL-4/IL-13-activated alternative macrophages. Together, this shows that alternative macrophages are essential during schistosomiasis for protection against organ injury through downregulation of egg-induced inflammation.