Bias of the Immune Response to \u3ci\u3ePneumocystis murina\u3c/i\u3e Does Not Alter the Ability of Neonatal Mice to Clear the Infection

Newborn mice are unable to clear Pneumocystis (PC) infection with the same efficiency as adults due, in part, to their inability to develop a robust immune response to infection until three weeks of age. It is known that infants tend develop a Th2 skewed response to antigen so we sought to determine whether a biased cytokine response altered the clearance of PC infection in neonatal mice. P. murina infection in neonatal mice resulted in increased IL-4 expression by CD4 T cells and myeloid cells, augmented IL-13 secretion within the airways and increased arginase activity in the airways, indicative of Th2-type responses. P. murina-infected IL-4Rα−/− neonates had a shift towards Th1 cytokine production and increased numbers of CD4 and CD8 T cells within the lung as well as elevated levels of P. murina-specific IgG. IFNγ−/− and IL-23 p19−/− mice had altered CD4-T cell-dependent cytokine and cell responses. Though we could alter the T helper cell environment in neonatal knockout mice, there was no loss in the ability of these pups to clear infection. It is possible that the Th2 phenotype normally seen in neonatal mice protects the developing lung from pro-inflammatory immune responses without compromising host defense against P. murina

\u3cem\u3ePneumocystis\u3c/em\u3e Infection Alters the Activation State of Pulmonary Macrophages

Recent studies show a substantial incidence of Pneumocystis jirovecii colonization and infection in patients with chronic inflammatory lung conditions. However, little is known about the impact of Pneumocystis upon the regulation of pulmonary immunity. We demonstrate here that Pneumocystis polarizes macrophages towards an alternatively activated macrophage-like phenotype. Genetically engineered mice that lack the ability to signal through IL-4 and IL-13 were used to show that Pneumocystis alternative macrophage activation is dependent upon signaling through these cytokines. To determine whether Pneumocystis-induced macrophage polarization would impact subsequent immune responses, we infected mice with Pneumocystis and then challenged them with Pseudomonas aeruginosa 14 days later. In co-infected animals, a higher proportion of macrophages in the alveolar and interstitial spaces expressed both classical and alternatively activated markers and produced the regulatory cytokines TGFβ and IL-10, as well as higher arginase levels than in mice infected with P. aeruginosa alone. Our results suggest that Pneumocystis reprograms the overall macrophage repertoire in the lung to that of a more alternatively-activated setpoint, thereby altering subsequent immune responses. These data may help to explain the association between Pneumocystis infection and decline in pulmonary function

Bias of the Immune Response to Pneumocystis murina Does Not Alter the Ability of Neonatal Mice to Clear the Infection

Newborn mice are unable to clear Pneumocystis (PC) infection with the same efficiency as adults due, in part, to their inability to develop a robust immune response to infection until three weeks of age. It is known that infants tend develop a Th2 skewed response to antigen so we sought to determine whether a biased cytokine response altered the clearance of PC infection in neonatal mice. P. murina infection in neonatal mice resulted in increased IL-4 expression by CD4 T cells and myeloid cells, augmented IL-13 secretion within the airways and increased arginase activity in the airways, indicative of Th2-type responses. P. murina-infected IL-4Rα−/− neonates had a shift towards Th1 cytokine production and increased numbers of CD4 and CD8 T cells within the lung as well as elevated levels of P. murina-specific IgG. IFNγ−/− and IL-23 p19−/− mice had altered CD4-T cell-dependent cytokine and cell responses. Though we could alter the T helper cell environment in neonatal knockout mice, there was no loss in the ability of these pups to clear infection. It is possible that the Th2 phenotype normally seen in neonatal mice protects the developing lung from pro-inflammatory immune responses without compromising host defense against P. murina

The Toll–Like Receptor 2/6 Agonist, FSL–1 Lipopeptide, Therapeutically Mitigates Acute Radiation Syndrome

Abstract Risks of radiation exposure from nuclear incidents and cancer radiotherapy are undeniable realities. These dangers urgently compel the development of agents for ameliorating radiation–induced injuries. Biologic pathways mediated by myeloid differentiation primary response gene 88 (MyD88), the common adaptor for toll–like receptor (TLR) and Interleukin–1 receptor signaling, are critical for radioprotection. Treating with agonists prior to radiation enhances survival by activating TLR signaling, whereas radiomitigating TLR–activating therapeutics given after exposure are less defined. We examine the radiomitigation capability of TLR agonists and identify one that is superior for its efficacy and reduced toxic consequences compared to other tested agonists. We demonstrate that the synthetic TLR2/6 ligand Fibroblast–stimulating lipopeptide (FSL–1) substantially prolongs survival in both male and female mice when administered 24 hours after radiation and shows MyD88–dependent function. FSL–1 treatment results in accelerated hematopoiesis in bone marrow, spleen and periphery, and augments systemic levels of hematopoiesis–stimulating factors. The ability of FSL–1 to stimulate hematopoiesis is critical, as hematopoietic dysfunction results from a range of ionizing radiation doses. The efficacy of a single FSL–1 dose for alleviating radiation injury while protecting against adverse effects reveals a viable radiation countermeasures agent

A noncanonical function of cGAMP in inflammasome priming and activation

Recognition of pathogen-associated molecular patterns and danger-associated molecular patterns by host cells is an important step in innate immune activation. The DNA sensor cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase (cGAS) binds to DNA and produces cGAMP, which in turn binds to stimulator of interferon genes (STING) to activate IFN-I. Here we show that cGAMP has a noncanonical function in inflammasome activation in human and mouse cells. Inflammasome activation requires two signals, both of which are activated by cGAMP. cGAMP alone enhances expression of inflammasome components through IFN-I, providing the priming signal. Additionally, when combined with a priming signal, cGAMP activates the inflammasome through an AIM2, NLRP3, ASC, and caspase-1 dependent process. These two cGAMP-mediated functions, priming and activation, have differential requirements for STING. Temporally, cGAMP induction of IFN-I precedes inflammasome activation, which then occurs when IFN-I is waning. In mice, cGAS/cGAMP amplify both inflammasome and IFN-I to control murine cytomegalovirus. Thus, cGAMP activates the inflammasome in addition to IFN-I, and activation of both is needed to control infection by a DNA virus

Pneumocystis infection alters the activation state of pulmonary macrophages

Recent studies show a substantial incidence of Pneumocystis jirovecii colonization and infection in patients with chronic inflammatory lung conditions. However, little is known about the impact of Pneumocystis upon the regulation of pulmonary immunity. We demonstrate here that Pneumocystis polarizes macrophages towards an alternatively activated macrophage-like phenotype. Genetically engineered mice that lack the ability to signal through IL-4 and IL-13 were used to show that Pneumocystis alternative macrophage activation is dependent upon signaling through these cytokines. To determine whether Pneumocystis-induced macrophage polarization would impact subsequent immune responses, we infected mice with Pneumocystis and then challenged them with Pseudomonas aeruginosa 14 days later. In co-infected animals, a higher proportion of macrophages in the alveolar and interstitial spaces expressed both classical and alternatively activated markers and produced the regulatory cytokines TGFβ and IL-10, as well as higher arginase levels than in mice infected with P. aeruginosa alone. Our results suggest that Pneumocystis reprograms the overall macrophage repertoire in the lung to that of a more alternatively-activated setpoint, thereby altering subsequent immune responses. These data may help to explain the association between Pneumocystis infection and decline in pulmonary function