Missense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can cause late-onset Parkinson disease. Past studies have provided conflicting evidence for the protective effects of LRRK2 knockdown in models of Parkinson disease as well as other disorders. These discrepancies may be caused by uncertainty in the pathobiological mechanisms of LRRK2 action. Previously, we found that LRRK2 knockdown inhibited proinflammatory responses from cultured microglia cells. Here, we report LRRK2 knockout rats as resistant to dopaminergic neurodegeneration elicited by intracranial administration of LPS. Such resistance to dopaminergic neurodegeneration correlated with reduced proinflammatory myeloid cells recruited in the brain. Additionally, adeno-associated virus-mediated transduction of human α-synuclein also resulted in dopaminergic neurodegeneration in wild-type rats. In contrast, LRRK2 knockout animals had no significant loss of neurons and had reduced numbers of activated myeloid cells in the substantia nigra. Although LRRK2 expression in the wild-type rat midbrain remained undetected under nonpathological conditions, LRRK2 became highly expressed in inducible nitric oxide synthase (iNOS)-positive myeloid cells in the substantia nigra in response to α-synuclein overexpression or LPS exposures. Our data suggest that knocking down LRRK2 may protect from overt cell loss by inhibiting the recruitment of chronically activated proinflammatory myeloid cells. These results may provide value in the translation of LRRK2-targeting therapeutics to conditions where neuroinflammation may underlie aspects of neuronal dysfunction and degeneration.M issense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can be found in many families that transmit classical late-onset Parkinson disease (PD) from one generation to the next. Notably, these mutations are prevalent in the Ashkenazi Jewish and North African Arab Berber populations in more than 20% of PD cases (1, 2). Genome-wide association studies further provide evidence that links LRRK2 to PD susceptibility, with several risk alleles being identified in LRRK2 (3, 4). Association studies have also linked LRRK2 to Crohn disease and Hansen disease (5, 6). Although LRRK2 is widely considered an exciting target for therapeutic approaches in PD, the pathobiological role of LRRK2 as a critical modifier of disease susceptibility is not well understood. Additional insights into LRRK2-linked molecular pathways relevant to PD and neurodegeneration may enable more predictive preclinical studies.PD is pathologically characterized by both α-synuclein inclusions called Lewy bodies and Lewy neurites and the profound loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The absence of LRRK2 has been shown to impair α-synuclein inclusion formation, neuron loss, and microglia activation in mice overexpressing mutant α-synuclein (7). However, other studies that have crossed LRRK2 knockout mice with different α-synuclein transgenic mice did not observe robust protection fr...

Asthmatics sensitized to fungi are reported to have more severe asthma, yet the immunopathogenic pathways contributing to this severity have not been identified. In a pilot assessment of human asthmatics, those subjects sensitized to fungi demonstrated elevated levels of the common γ-chain cytokine IL-7 in lung lavage fluid, which negatively correlated with the lung function measurement PC20. Subsequently, we show that IL-7 administration during experimental fungal asthma worsened lung function and increased the levels of type 2 cytokines (IL-4, IL-5, IL-13), proallergic chemokines (CCL17, CCL22) and proinflammatory cytokines (IL-1α, IL-1β). Intriguingly, IL-7 administration also increased IL-22, which we have previously reported to drive immunopathogenic responses in experimental fungal asthma. Employing IL22R26R reporter mice, we identified γδ T cells, iNKT cells, CD4 T cells and ILC3s as sources of IL-22 during fungal asthma; however, only iNKT cells were significantly increased after IL-7 administration. IL-7-induced immunopathogenesis required both type 2 and IL-22 responses. Blockade of IL-7Rα in vivo resulted in attenuated IL-22 production, lower CCL22 levels, decreased iNKT cell, CD4 T-cell and eosinophil recruitment, yet paradoxically increased dynamic lung resistance. Collectively, these results suggest a complex role for IL-7 signaling in allergic fungal asthma.

Members of the IL-1 family play protective and regulatory roles in immune defense against the opportunistic mold Aspergillus fumigatus. Here, we investigated the IL-1 family member IL-33 in lung defense against A. fumigatus. IL-33 was detected in the naïve lung, which further increased after exposure to A. fumigatus in a Dectin-1 independent manner. Mice deficient in the receptor for IL-33 (Il1rl1−/−) unexpectedly demonstrated enhanced lung clearance of A. fumigatus. IL-33 functioned as a negative regulator of multiple inflammatory cytokines, as IL-1α, IL-1β, IL-6, IL-17A and IL-22 were significantly elevated in fungal-exposed Il1rl1−/− mice. Subsequently, IL-33 administration to normal mice attenuated fungal-induced IL-17A and IL-22, but not IL-1α, IL-1β and IL-6 production. IL-33 mediated regulation of IL-17A and IL-22 did not involve the modulation of IL-23 but rather prostaglandin E2 (PGE2); PGE2 was significantly increased in fungal-exposed Il1rl1−/− mice and normal mice produced less PGE2 after fungal exposure when administered IL-33, suggesting that IL-33 mediated regulation of IL-17A and IL-22 occurred at the level of PGE2. This was confirmed by in vivo cyclooxygenase 2 (COX-2) inhibition, which attenuated fungal-induced IL-17A and IL-22, as well as IL-1α, IL-1β and IL-6 production, in Il1rl1−/− mice resulting in impaired fungal clearance. We also show that a PGE2 receptor agonist increased, whereas a PGE2 synthase inhibitor decreased, the levels of IL-17A and IL-22, but not IL-1α, IL-1β and IL-6. This study establishes novel mechanisms of induction of innate IL-17A/IL-22 production via PGE2 and regulation of the PGE2-IL-17A-IL-22 axis via IL-33 signaling during lung fungal exposure.

Chitin is a polysaccharide that provides structure and rigidity to the cell walls of fungi and insects. Mammals possess multiple chitinases, which function to degrade chitin, thereby supporting a role for chitinases in immune defense. However, chitin degradation has been implicated in the pathogenesis of asthma. Here, we determined the impact of acidic mammalian chitinase (AMCase) () deficiency on host defense during acute exposure to the fungal pathogen as well as its contribution to-associated allergic asthma. We demonstrate that chitin in the fungal cell wall was detected at low levels in conidia, which emerged at the highest level during hyphal transition. In response to acute challenge, mice unexpectedly demonstrated lower lung burdens at 2 days postchallenge. The lower fungal burden correlated with decreased lung interleukin-33 (IL-33) levels yet increased IL-1β and prostaglandin E (PGE) production, a phenotype that we reported previously to promote the induction of IL-17A and IL-22. During chronic exposure, AMCase deficiency resulted in lower dynamic and airway lung resistance than in wild-type mice. Improved lung physiology correlated with attenuated levels of the proallergic chemokines CCL17 and CCL22. Surprisingly, examination of inflammatory responses during chronic exposure revealed attenuated IL-17A and IL-22 responses, but not type 2 responses, in the absence of AMCase. Collectively, these data suggest that AMCase functions as a negative regulator of immune responses during acute fungal exposure and is a contributor to fungal asthma severity, putatively via the induction of proinflammatory responses.

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Humans are constantly exposed to the opportunistic mold and disease caused by this pathogen is often determined by the magnitude of local and systemic immune responses. We have previously shown a protective role for IL-22 after acute exposure. Here, employing IL22R26R reporter mice, we identified iNKT cells, γδ T cells and ILC3 cells as lung cell sources of IL-22 in response to acute exposure. As these cells often utilize common γ-chain cytokines for their development or maintenance, we determined the role of IL-7, IL-21 and IL-15 on lung IL-22 induction and lung clearance. We observed that IL-7, IL-21 and IL-15 were essential, partially required or negatively regulated the production of IL-22, respectively. Deficiency in IL-7 and IL-21, but not IL-15R, resulted in impaired fungal clearance. Surprisingly however, the absence of IL-7, IL-21 or IL-15R signaling had no effect on neutrophil recruitment. The levels of IL-1α, an essential anti- proinflammatory cytokine, were increased in the absence of IL-7 and IL-15R, but decreased in the absence of IL-21. IL-7 was responsible for maintaining lung iNKT cells and γδ T cells whereas IL-21 was responsible for maintaining lung iNKT cells and ILC3s. In contrast, IL-15R deficiency had no effect on the absolute numbers of any IL-22 cell source, rather resulting in enhanced per cell production of IL-22 by iNKT cells and γδ T cells. Collectively, these results provide insight into how the IL-22 response in the lung is shaped after acute exposure.

The authors discovered mislabeled axes in Fig. 6C. Specifically, the y-axis should read "pg/ml (lung digest cells-48 h)" instead of "IL-22 pg/ml (lung digest cells-48 h)." In addition, "IL-1a" and "IL-1b" should be included on the x-axis.

Individuals that present with difficult-to-control asthma and sensitivity to one or more fungal species are categorized as a subset of severe asthma patients belonging to a group herein referred to as severe asthma with fungal sensitization (SAFS). We have previously reported the identification of numerous cytokines and chemokines that were elevated in human asthmatics that were sensitized to fungi vs. non-fungal sensitized asthmatics. Here, we show that the unique chemokine CX3CL1 (fractalkine) is elevated in both bronchoalveolar lavage fluid and sputum from human asthmatics sensitized to fungi, implicating an association with CX3CL1 in fungal asthma severity. In an experimental model of fungal-associated allergic airway inflammation, we demonstrate that the absence of CX3CR1 signaling unexpectedly resulted in a profound impairment in lung function. Histological assessment of lung tissue revealed an unrestricted inflammatory response that was subsequently characterized by enhanced levels of neutrophils, eosinophils and inflammatory monocytes. Neutrophilic inflammation correlated with elevated IL-17A, proinflammatory cytokines (TNF-α, IL-1α IL-1β), neutrophil survival factors (G-CSF) and neutrophil-targeting chemokines (CCL3, CCL4). Eosinophilia correlated with elevated type 2 responses (IL-5, IL-13) whereas inflammatory monocyte levels correlated with elevated type 1 responses (IFN-γ, CXCL9) and survival factors (M-CSF). Despite enhanced inflammatory responses, the immunoregulatory cytokine IL-10 and the natural inhibitor of IL-1 signaling, IL-1RA, were significantly elevated rather than impaired. Regulatory T cell levels were unchanged, as were levels of the anti-inflammatory cytokines IL-35 and IL-38. Taken together, the CX3CL1/CX3CR1 axis preserves lung function during fungal-associated allergic airway inflammation through a non-classical immunoregulatory mechanism.