Pathways of macrophage activation and innate immunity

WNT/β-catenin pathway is modulated in asthma patients and LPS-stimulated RAW264.7 macrophage cell line

In the present study, we investigated the possibility that the WNT/β-catenin pathway plays a role in inflammatory responses both in an human inflammatory condition and in an in vitro inflammation model. First, we analyzed gene expression patterns of the peripheral blood cells from asthma patients compared with those from normal subjects using microarray analyses. We found that intracellular signaling molecules of the WNT/β-catenin pathway were significantly changed in asthma patients compared with the levels in the controls. Next, we determined whether major components of the WNT/β-catenin pathway were involved in the lipopolysaccharide (LPS)-induced inflammatory response of the RAW264.7 macrophage cell line. Among the members of WNT/β-catenin pathway, the protein levels of low-density lipoprotein receptor-related protein (LRP) 6, dishevelled (DVL) 2, and AXIN1, which were measured using western blotting, did not significantly change in the presence of LPS. In contrast, the LPS induced a rapid phosphorylation of glycogen synthase kinase (GSK) 3β and accumulation of β-catenin protein. It was found that β-catenin plays a significant role in the LPS-induced inflammatory response through the performance of small interfering RNA (siRNA) transfection experiments. The mRNA level of IL-6 was significantly elevated in β-catenin siRNA-transfected cells compared with that in control siRNA-transfected cells after LPS treatment. Furthermore, nuclear factor-κB (NF-κB) activity was also significantly increased in β-catenin siRNA-transfected cells compared with the level seen in control siRNA-transfected cells. Taken together, these results suggest that β-catenin plays a role as a negative regulator, preventing the overproduction of inflammatory cytokines such as IL-6 in LPS-induced inflammatory responses.

The host resistance locus sst1 controls innate immunity to Listeria monocytogenes infection in immunodeficient mice

Epidemiological, clinical, and experimental approaches have convincingly demonstrated that host resistance to infection with intracellular pathogens is significantly influenced by genetic polymorphisms. Using a mouse model of infection with virulent Mycobacterium tuberculosis (MTB), we have previously identified the sst1 locus as a genetic determinant of host resistance to tuberculosis. In this study we demonstrate that susceptibility to another intracellular pathogen, Listeria monocytogenes, is also influenced by the sst1 locus. The contribution of sst1 to anti-listerial immunity is much greater in immunodeficient scid mice, indicating that this locus controls innate immunity and becomes particularly important when adaptive immunity is significantly depressed. Similar to our previous observations using infection with MTB, the resistant allele of sst1 prevents formation of necrotic infectious lesions in vivo. We have shown that macrophages obtained from sst1-resistant congenic mice possess superior ability to kill L. monocytogenes in vitro. The bactericidal effect of sst1 is dependent on IFN-gamma activation and reactive oxygen radical production by activated macrophages after infection, but is independent of NO production. It is possible that there is a single gene that controls common IFN-dependent macrophage function, which is important in the pathogenesis of infections caused by both MTB and L. monocytogenes. However, host resistance to the two pathogens may be controlled by two different polymorphic genes encoded within the sst1 locus. The polymorphic gene(s) encoded within the sst1 locus that controls macrophage interactions with the two intracellular pathogens remains to be elucidated.

Resistance to acute babesiosis is associated with interleukin-12- and gamma interferon-mediated responses and requires macrophages and natural killer cells

We examined the role of the cytokines gamma interferon (IFN-gamma) and interleukin-12 (IL-12) in the model of acute babesiosis with the WA1 Babesia. Mice genetically deficient in IFN-gamma-mediated responses (IFNGR2KO mice) and IL-12-mediated responses (Stat4KO mice) were infected with the WA1 Babesia, and observations were made on the course of infection and cytokine responses. Levels of IFN-gamma and IL-12 in serum increased 24 h after parasite inoculation. The augmented susceptibility observed in IFNGR2KO and Stat-4KO mice suggests that the early IL-12- and IFN-gamma-mediated responses are involved in protection against acute babesiosis. Resistance appears to correlate with an increase in nitric oxide (NO) production. In order to assess the contribution of different cell subsets to resistance against the parasite, we also studied mice lacking B cells, CD4+ T cells, NK cells, and macrophages. Mice genetically deficient in B lymphocytes or CD4+ T lymphocytes were able to mount protective responses comparable to those of immunosufficient mice. In contrast, in vivo depletion of macrophages or NK cells resulted in elevated susceptibility to the infection. Our observations suggest that a crucial part of the response that protects from the pathogenic Babesia WA1 is mediated by macrophages and NK cells, probably through early production of IL-12 and IFN-gamma, and induction of macrophage-derived effector molecules like NO.

Innate resistance to Babesia infection is influenced by genetic background and gender

Infection of severe combined immunodeficient mice with Babesia sp. strain WA1 was studied to assess the contributions of innate and adaptive immunity in resistance to acute babesiosis. The scid mutation showed little effect in genetically susceptible C3H mice and did not decrease the inherent resistance of C57BL/6 mice to the infection, suggesting that innate immunity plays a central role in determining the course of Babesia infection in these strains. In contrast, the scid mutation dramatically impaired resistance in moderately susceptible BALB/c mice, suggesting that acquired immunity may play an important secondary role. In comparison to their female counterparts, male mice of different genetic backgrounds showed increased resistance to the infection, indicating that the gender of the host may influence protection against babesiosis.

A Monoclonal Antibody Directed Against the Murine Macrophage Surface Molecule F4/80 Modulates Natural Immune Response to Listeria monocytogenes

Whole spleen cell cultures from SCID mice release high levels of IFN-γ when exposed to heat-killed Listeria monocytogenes (HKL). This microbe-induced and T cell-independent response depends on both macrophages (MΦ) and NK cells: HKL-stimulated MΦ release TNF-α and IL-12, which together activate NK cells for IFN-γ release. We show here that this cytokine-mediated activation cascade can be modulated by a mAb against the MΦ surface glycoprotein F4/80. HKL-induced IL-12, TNF-α, and IFN-γ in SCID whole spleen cell cultures was inhibited by coincubation with anti-F4/80 mAb whereas IL-1 and IL-10 were enhanced. Both effects were apparent at mRNA and protein release levels. Whereas inhibitory activities were F4/80 Ag specific, stimulatory effects were Fc dependent and nonspecific. Furthermore, cytokine inhibition by anti-F4/80 was only apparent when MΦ and NK cells were present simultaneously and in close vicinity, indicating that direct cell-to-cell contact is a prerequisite. These data suggest a novel pathway for microbe-induced MΦ/NK cell interaction involving direct cell-to-cell signaling and give the first evidence for a functional role of the MΦ surface glycoprotein F4/80.

Immunity to Asexual Blood Stages of Plasmodium: Is Resistance to Acute Malaria Adaptive or Innate?

Current models of immunity to blood stages of Plasmodium invoke a primary role for T-cell dependent processes and much recent evidence implicates Th1-type responses as crucial to the control of acute malaria. But do these data stand up to close scrutiny? Here, Andy Fell and Nick Smith review recent data from rodent and human studies and suggest that Th1-type responses may not after all be important in controlling malaria infection in the blood.

The expression of cytokine mRNA in the cauda equina of Lewis rats with experimental allergic neuritis

Autoreactive CD4+ T cells can transfer experimental allergic neuritis (EAN) to naive recipients. In order to further analyze the role of these T cells and their corresponding cytokines in EAN, we studied the expression of mRNA for IFN-gamma, IL-4, and IL-10 in the cauda equina of rats with EAN using a quantitative competitive reverse transcriptase PCR method. Nerves were studied on days 0 (pre-immunization), 10 (disease onset), 13 (clinical progression), 16 (disease peak), as well as 20, 24, and 34 post immunization (recovery). IFN-gamma messages increased at disease onset and peaked at day 13 p.i. IL-10 message remained at a very low level at disease onset and surged at day 16. Both messages were low in recovery stage. IL-4 message was undetectable at any time point. These data suggest a pro-inflammatory role of IFN-gamma and anti-inflammatory role of IL-10 in EAN lesions. It is also possible that a clonal switch from Th1 to Th2 occurs in EAN lesions during the disease course.