Highlights d L. pneumophila injects LamA, which degrades host cell glycogen d LamA has evolved to interfere with amoebae host-specific processes d In the amoebae natural host, LamA subverts encystation to promote a permissive host d In humans, LamA triggers accidental inflammatory responses and nutritional immunity

The role of the type 2 helper T cell (Th2)-polarizing cytokines IL-4 and IL-10 has not yet been studied in P0106-125-induced murine experimental autoimmune neuritis (EAN). We, therefore, addressed the functional relevance of these cytokines and signaling via the IL-4-associated transcription factor STAT6. The clinical course of P0106-125-induced EAN in mice deficient for IL-10(0/0), IL-4(0/0), or STAT6(0/0) was significantly aggravated compared with that of wild-type control mice. In addition, treatment of P0106-125-immunized C57BL/6 mice at the onset of clinical symptoms with a monoclonal IL-10 neutralizing antibody aggravated symptoms and prolonged disease to a similar degree as in IL-10(0/0) mice. This exacerbated course was attributed to a more prominent Th1 immune response associated with a persistent M1 milieu in the sciatic nerve and in the regional and systemic lymphatic system. These data suggest a Th2-polarized milieu being required to prevent axonal damage of the sciatic nerve and to terminate the P0106-125-specific immune response in EAN. Beyond the already known role of macrophages as pathogenic effector cells in EAN, these data suggest that M2-differentiated macrophages do not damage and may even protect neural tissues in EAN. Thus, these data highlight the pathogenetic relevance of the macrophage polarization status in EAN. Therapeutic modulation of immune responses from an M1 toward an M2 milieu may be a promising novel strategy in peripheral nervous system neuritis.

These data suggest differential and hierarchically ordered roles for CXCR4/CXCL12- vs. CXCR7/CXCL12-dependent effects during EAN: CXCR7/CXCL12 interaction is a gatekeeper for pathogenic cells, regardless of their CXCR4/CXCL12-dependent state of activation.

Myelin protein 0 peptide 106-125-induced murine experimental autoimmune neuritis (EAN) is a CD4-positive T cell-mediated monophasic axonal inflammatory neuropathy; interferon-γ is the key proinflammatory mediator. Experimental autoimmune neuritis is well suited for elucidating pathogenetic mechanisms underlying human acute axonal Guillain-Barré syndrome. Here, the functional role of the costimulatory molecule CD40 was defined by characterization of EAN in CD40-deficient mice. In contrast to immunized C57BL/6 mice, CD40-deficient mice were resistant to EAN owing to impaired priming of CD4-positive T-effector cells. To determine whether CD40 is a suitable candidate for the treatment of EAN, we administered monoclonal anti-CD40 antibody either before immunization or upon onset of neurologic signs. Prophylactic anti-CD40 treatment completely abolished CD4-positive T-cell priming. Therapeutic application of anti-CD40 prevented full activation of CD4-positive T cells that were in the process of priming and suppressed production of interferon-γ in peripheral lymph nodes, spleen, and serum, and of interleukin-6, interleukin-12p40, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1, which are associated with activation of the nuclear factor-κB signaling pathway. This resulted in enhanced recovery by early generation of CD25-positive, Foxp3-positive, CD4-positive regulatory T cells. Thus, these experiments highlight the crucial role of CD40 as an important costimulatory molecule in EAN and suggest that it has potential as a therapeutic target in human neuritis.

The functional relevance of the innate immune system has not yet been dissected in P0-induced murine experimental autoimmune neuritis. Therefore, the role of Toll-like receptor (TLR) 2, TLR4, myeloid differentiation response gene 88, and Toll-IL-1 receptor domain-containing adaptor-inducing interferon-γ (TRIF), factors critically involved in the TLR signaling pathway, was studied in experimental autoimmune neuritis. In the absence of TLR2, TLR4, myeloid differentiation response gene 88, or TRIF, the clinical course was significantly attenuated compared to wild-type mice. This could be attributed to impaired NF-κB activation, as shown by the absence of nuclear translocation of RelA with a decreased expression of IL-6, IL-12p40, and IL-17A. Remarkably, P0-immunized TLR2 mice exhibited a delayed recovery as compared to TLR4 mice, which was because of an impaired T helper cell 2 polarization. Immunized TLR2 mice were unable to induce OX40 and OX40L by matrix metalloproteinase-2 on splenic dendritic cells. Subsequently, M2 polarization was impaired and macrophages were unable to sufficiently induce T regulatory cells (T). Thus, in the recovery phase, T were significantly increased in TLR4 mice as compared to wild-type mice, whereas T in immunized TLR2 mice were only slightly increased. Our data highlight the relevance of innate immunity and, especially, the tight interaction between the innate and the adaptive immune system, which should be considered for therapeutic approaches of autoimmune diseases.

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Legionellae are gram-negative bacteria most commonly found in freshwater ecosystems and purpose-built water systems. In humans, the bacterium causes Legionnaires’ disease (LD) or a Pontiac fever. In this study, the different waters (drinking water, pool water, cooling towers) in which Legionella pneumophila has been isolated were studied to assess the possible risk of bacterial spreading in the population. The influence of physical and chemical parameters, and interactions with Acanthamoeba castellanii on L. pneumophila, were analyzed by Heterotrophic Plate Count, the Colony-forming units (CFU) methods, transmission electron microscopy (TEM), and Sequence-Based Typing (SBT) analysis. During the study period (2013–2019), a total of 1932 water samples were analyzed, with the average annual rate of Legionella-positive water samples of 8.9%, showing an increasing trend. The largest proportion of Legionella-positive samples was found in cooling towers and rehabilitation centers (33.9% and 33.3%, respectively). Among the isolates, L. pneumophila SGs 2–14 was the most commonly identified strain (76%). The survival of Legionella was enhanced in the samples with higher pH values, while higher electrical conductivity, nitrate, and free residual chlorine concentration significantly reduced the survival of Legionella. Our results show that growth in amoeba does not affect the allelic profile, phenotype, and morphology of the bacterium but environmental L. pneumophila becomes more resistant to pasteurization treatment.

The amoeba Dictyostelium discoideum has been used as a model organism to study host-pathogen interaction in many intracellular bacteria. Francisella tularensis is a Gram-negative, highly infectious bacterium that causes the zoonotic disease tularemia. The bacterium is able to replicate in different phagocytic and nonphagocytic cells including mammalian, amoebae, and arthropod cells. The aim of this study was to determine the optimal temperature and infection dose in the interaction of Francisella novicida with D. discoideum in order to establish a model of Francisella infection in the social amoeba. The amoeba cells were infected with a different multiplicity of infection (5, 10, and 100) and incubated at different temperatures (22, 25, 27, 30, and 37°C). The number of intracellular bacteria within D. discoideum, as well as cytotoxicity, was determined at 2, 4, 24, 48, and 72 hours after infection. Our results showed that the optimal temperature for Francisella intracellular replication within amoeba is 30°C with the MOI of 10. We can conclude that this MOI and temperature induced the optimal growth of bacteria in Dictyostelium with low cytotoxicity.