Critical role of the neutrophil-associated high-affinity receptor for IgE in the pathogenesis of experimental cerebral malaria.

The role of the IgE-FcεRI complex in malaria severity in Plasmodium falciparum-hosting patients is unknown. We demonstrate that mice genetically deficient for the high-affinity receptor for IgE (FcεRIα-KO) or for IgE (IgE-KO) are less susceptible to experimental cerebral malaria (ECM) after infection with Plasmodium berghei (PbANKA). Mast cells and basophils, which are the classical IgE-expressing effector cells, are not involved in disease as mast cell-deficient and basophil-depleted mice developed a disease similar to wild-type mice. However, we show the emergence of an FcεRI(+) neutrophil population, which is not observed in mice hosting a non-ECM-inducing PbNK65 parasite strain. Depletion of this FcεRI(+) neutrophil population prevents ECM, whereas transfer of this population into FcεRIα-KO mice restores ECM susceptibility. FcεRI(+) neutrophils preferentially home to the brain and induce elevated levels of proinflammatory cytokines. These data define a new pathogenic mechanism of ECM and implicate an FcεRI-expressing neutrophil subpopulation in malaria disease severity.

Neonatal lung immune responses show a shift of cytokines and transcription factors toward Th2 and a deficit in conventional and plasmacytoid dendritic cells.

The high incidence of lung-damaging life-threatening respiratory infections in infants may be related to the immaturity of their immune systems. To determine whether lung immune features differ in early life compared with those in adulthood, whole lung as well as lung T lymphocyte and DC responses were investigated in BALB/c neonates versus adults. Higher expression of GATA-3 and rapid and sustained production of type 2 cytokines by lung explants after in vitro exposure to anti-CD3 was the hallmark of the neonatal period, suggestive of a Th2 bias. Neonatal lung GATA-3-producing cells were identified as CD3(+), CD4 and CD8 double-negative T lymphocytes, a subset found at a higher frequency in neonatal than adult lung. The neonatal lungs contained fewer conventional DCs, with a lower ratio of CD103(+) to CD11b(+) DCs, and a much lower number of plasmacytoid DCs in comparison with adult lungs. Yet, when stimulated in vivo by BCG, neonatal lung DCs matured and primed adult naïve CD4(+) T cells toward Th1 as efficiently as adult BCG-primed lung DCs. Conversely, both adult and neonatal BCG-primed lung DCs induced a Th2 cytokine response from neonatal naïve lymph node T cells, suggestive of an intrinsic feature of neonatal T lymphocytes.

Mycobacterium bovis Bacillus Calmette-Guérin killed by extended freeze-drying reduces colitis in mice.

BACKGROUND & AIMS: Mycobacterium bovis Bacillus Calmette-Guérin (BCG), killed by extended freeze-drying (EFD), induces secretion of interleukin-10 and reduces lung inflammation in a mouse model of asthma. We investigated the effects of EFD BCG in mouse models of inflammatory bowel disease. METHODS: EFD BCG was administered subcutaneously to mice with colitis induced by dextran sodium sulfate (DSS), oxazolone, or adoptive transfer of CD4(+)CD45RB(high)Foxp3(-) T cells from C57Bl/6 Foxp3GFP mice to RAG2(-/-) mice. RESULTS: EFD BCG, administered either before induction of DSS and oxazolone colitis or after development of acute or chronic DSS-induced colitis, reduced symptom scores, loss of body weight, and inflammation. Although transfer of CD4(+)CD45RB(high)Foxp3(-) cells induced colitis in RAG2(-/-) mice, administration of EFD BCG at the time of the transfer converted Foxp3(-) T cells to Foxp3(+) T cells and the mice did not develop colitis. EFD BCG protected mice from colitis via a mechanism that required expansion of T regulatory cells and production of interleukin-10 and transforming growth factor ß. EFD BCG activated the retinoid X receptor (RXR)-α-peroxisome proliferator-activated receptor (PPAR)-γ heterodimer, blocked translocation of nuclear factor κB to the nucleus, and reduced colonic inflammation; it did not increase the number of colon tumors that formed in mice with chronic DSS-induced colitis. CONCLUSIONS: EFD BCG controls severe colitis in mice by expanding T regulatory cell populations and PPAR-γ and might be developed to treat patients with inflammatory bowel disease.

Sorting of Leishmania-bearing dendritic cells reveals subtle parasite-induced modulation of host-cell gene expression.

Once in the mouse skin, Leishmania (L) amazonensis amastigotes are hosted by professional mononuclear phagocytes such as dendritic cells (DCs). When monitored after parasite inoculation, the frequency of amastigote-hosting DCs is very low (<1%) in both the skin and skin-draining lymph nodes. Therefore, we designed and validated an efficient procedure to purify live amastigotes-hosting DCs with the objective to facilitate quantitative and qualitative analysis of such rare cells. To this end, a L. amazonensis transgenic parasite expressing DsRed2 fluorescent protein was generated and added to mouse bone marrow-derived DC cultures. Then, a high speed sorting procedure, performed in BSL-2 containment, was setup to pick out only DCs hosting live amastigotes. This study reveals, for the first time, a unique transcript pattern from sorted live amastigotes-hosting DCs that would have been undetectable in unsorted samples. It was indeed possible to highlight a significant and coordinated up-regulation of L-arginine transporter and arginase2 transcripts in Leishmania-hosting DCs compared to un-parasitized DCs. These results indicate that arginine catabolism for polyamine generation is dominating over L-arginine catabolism for NO generation. In conclusion, this approach provides a powerful method for further characterisation, of amastigote-hosting DCs in the skin and the skin-draining lymph nodes.

Dendritic cells recruited to the lung shortly after intranasal delivery of Mycobacterium bovis BCG drive the primary immune response towards a type 1 cytokine production.

We showed in a previous study that the intranasal (i.n) delivery of bacille Calmette-Guérin (BCG) to BP2 mice (H-2q) inhibits eosinophilia and bronchial hyperreactivity in a mouse model of asthma. The present work has been performed to characterize the leucocyte lineages recruited to the lungs of mice after i.n. delivery of BCG and potentially involved in the polarization of T lymphocytes. The different antigen-presenting cells (APC) recruited to bronchoalveolar lavage (BAL) and to lung tissue of mice shortly after the delivery of BCG were analysed in parallel as well as their capacity to drive the immune response towards a T helper type 1 cytokine production. Alveolar macrophages (AM) from the BAL were CD11c+, F4/80+ and CD11b-, and in the lung tissue two major populations of potential APC were detected: one CD11c-, F4/80+, CD11b+ and I-Aq- was identified as interstitial macrophages (IM) and a second expressing CD11c+ and I-Aq+ antigens, negative for CD11b and F4/80 markers as leucocytic dendritic cells (DC). Freshly isolated DC up-regulated CD11b and CD40 antigens after overnight culture, but remained negative for CD8alpha antigen, suggesting a myeloid origin. Lung DC which produced high amount of interleukin (IL)-12 were potent inducers of naive CD4+ T lymphocyte priming, as assessed by interferon-gamma (IFN-gamma) production by these naive CD4+ T cells. Lung explants recovered long term after BCG delivery produced sustained levels of IFN-gamma. Our results suggest that AM and particularly DC by secreting IL-12 shortly after BCG delivery induce the long-term persistence of IFN-gamma-secreting T cells percolating in BCG-loaded lung tissue.