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Abstract Background Ribonuclease 8 is a member of the RNase A family of secretory ribonucleases; orthologs of this gene have been found only in primate genomes. RNase 8 is a divergent paralog of RNase 7, which is lysine-enriched, highly conserved, has prominent antimicrobial activity, and is expressed in both normal and diseased skin; in contrast, the physiologic function of RNase 8 remains uncertain. Here, we examine the genetic diversity of human RNase 8, a subject of significant interest given the existence of functional pseudogenes (coding sequences that are otherwise intact but with mutations in elements crucial for ribonucleolytic activity) in non-human primate genomes. Results RNase 8 expression was detected in adult human lung, spleen and testis tissue by quantitative reverse-transcription PCR. Only two single-nucleotide polymorphisms and four unique alleles were identified within the RNase 8 coding sequence; nucleotide sequence diversity (π = 0.00122 ± 0.00009 per site) was unremarkable for a human nuclear gene. We isolated transcripts encoding RNase 8 via rapid amplification of cDNA ends (RACE) and RT-PCR which included a distal potential translational start site followed by sequence encoding an additional 30 amino acids that are conserved in the genomes of several higher primates. The distal translational start site is functional and promotes RNase 8 synthesis in transfected COS-7 cells. Conclusions These results suggest that RNase 8 may diverge considerably from typical RNase A family ribonucleases and may likewise exhibit unique function. This finding prompts a reconsideration of what we have previously termed functional pseudogenes, as RNase 8 may be responding to constraints that promote significant functional divergence from the canonical structure and enzymatic activity characteristic of the RNase A family.

Abstract Background The innate immune responses of neonates differ dramatically from those of adults. Here we examine the acute inflammatory responses of neonatal and weanling mice infected with pneumonia virus of mice (PVM), a rodent pathogen (family Paramyxoviridae, genus Pneumovirus) that replicates the sequelae of severe respiratory syncytial virus infection. Results We demonstrate that virus replication proceeds indistinguishably in all age groups (inoculated at 1, 2, 3 and 4 weeks of age), although inflammatory responses vary in extent and character. Some of the biochemical mediators detected varied minimally with age at inoculation. Most of the mediators evaluated demonstrated elevated expression over baseline correlating directly with age at the time of virus inoculation. Among the latter group are CCL2, CCL3, and IFN-γ, all cytokines previously associated with PVM-induced inflammatory pathology in mature mice. Likewise, we detect neutrophil recruitment to lung tissue in all age groups, but recruitment is most pronounced among the older (3 - 4 week old) mice. Interestingly, all mice exhibit failure to thrive, lagging in expected weight gain for given age, including the youngest mice that present little overt evidence of inflammation. Conclusions Our findings among the youngest mice may explain in part the phenomenon of atypical or minimally symptomatic respiratory infections in human neonates, which may be explored further with this infection model.

Abstract Background We have shown previously that acute infection with the respiratory pathogen, pneumonia virus of mice (PVM), results in local production of the proinflammatory chemokine, CCL3, and that neutrophil recruitment in response to PVM infection is reduced dramatically in CCL3 -/- mice. Results In this work, we demonstrate that CCL3-mediated neutrophil recruitment is coordinated by interferon-gamma (IFNγ). Neutrophil recruitment in response to PVM infection was diminished five-fold in IFNγ receptor gene-deleted mice, although neutrophils from IFNγR -/- mice expressed transcripts for the CCL3 receptor, CCR1 and responded functionally to CCL3 ex vivo. Similarly, in the absence of PVM infection, CCL3 overexpression alone could not elicit neutrophil recruitment in the absence of IFNγ. Interestingly, although supplemental IFNγ restored neutrophil recruitment and resulted in a sustained weight loss among CCL3-overexpressing IFNγ -/- mice, CCL3-mediated neutrophil recruitment alone did not result in the pulmonary edema or respiratory failure characteristic of severe viral infection, suggesting that CCL3 and IFN-γ together are sufficient to promote neutrophil recruitment but not pathologic activation. Conclusion Our findings reveal a heretofore unrecognized hierarchical interaction between the IFNγ and CCL3, which demonstrate that IFNγ is crucial for CCL3-mediated neutrophil recruitment in vivo.

Eosinophils have broad and extensive immunomodulatory capacity; recent studies have focused on the roles of distinct eosinophil subsets in specific tissue microenvironments. Ly6G is a GPI‐linked leukocyte surface Ag understood primarily as a marker of mouse neutrophils, although its full function is not known. Here, we show that Ly6G/Gr1, detected by mAbs 1A8 (anti‐Ly6G) and RB6‐8C5 (anti‐Gr1), is detected prominently on a significant fraction of eosinophils from mouse bone marrow and bone marrow‐derived culture, with fractions expressing this Ag increasing in IL‐5‐enriched microenvironments. Among our findings, we identified SiglecF+Gr1+ eosinophils in bone marrow from naïve, allergen‐challenged and IL‐5 transgenic mice; SiglecF+Gr1+ eosinophils were also prominent ex vivo in bone marrow‐derived eosinophils (bmEos) in IL‐5‐enriched culture. Reducing the IL‐5 concentration 20‐fold had no impact on the rate of generation of SiglecF+ bmEos but did result in a marked increase in the Gr1− fraction (from 17.4 ± 2% to 30 ± 2.3%, ***P < 0.005). Reducing the IL‐5 concentration also enhanced chemotaxis; SiglecF+Gr1− bmEos were considerably more responsive to eotaxin‐1 than were their SiglecF+Gr1+ counterparts. These results suggest that (i) IL‐5 regulates the expression of Ly6G/Gr1, either directly or indirectly, in cells of the eosinophil lineage, (ii) eosinophils generated in response to high concentrations of IL‐5 can be distinguished from those generated under homeostatic conditions by expression of the Ly6G/Gr1 cell surface Ag, and (iii) expression of Ly6G/Gr1 may have an impact on function, directly or indirectly, including the potential to undergo chemotaxis in response to eotaxin‐1. [ABSTRACT FROM AUTHOR]

Eosinophil peroxidase (EPX) is a major constituent of the large cytoplasmic granules of both human and mouse eosinophilic leukocytes. Human EPX deficiency is a rare, autosomal‐recessive disorder limited to the eosinophil lineage. Our intent was to explore the impact of EPX gene deletion on eosinophil content, structure, and function. In response to repetitive intranasal challenge with a filtrate of the allergen, Alternaria alternata, we found significantly fewer eosinophils peripherally and in the respiratory tracts of EPX−/− mice compared to wild‐type controls; furthermore, both the major population (Gr1−/lo) and the smaller population of Gr1hi eosinophils from EPX−/− mice displayed lower median fluorescence intensities (MFIs) for Siglec F. Quantitative evaluation of transmission electron micrographs of lung eosinophils confirmed the relative reduction in granule outer matrix volume in cells from the EPX−/− mice, a finding analogous to that observed in human EPX deficiency. Despite the reduced size of the granule matrix, the cytokine content of eosinophils isolated from allergen‐challenged EPX−/− and wild‐type mice were largely comparable to one another, although the EPX−/− eosinophils contained reduced concentrations of IL‐3. Other distinguishing features of lung eosinophils from allergen‐challenged EPX−/− mice included a reduced fraction of surface TLR4+ cells and reduced MFI for NOD1. Interestingly, the EPX gene deletion had no impact on eosinophil‐mediated clearance of gram‐negative Haemophilus influenzae from the airways. As such, although no clinical findings have been associated with human EPX deficiency, our findings suggest that further evaluation for alterations in eosinophil structure and function may be warranted. Eosinophils from the lungs of allergen‐challenged EPX−/− mice display differential expression of Siglec F and maintain reduced quantities of IL‐3. [ABSTRACT FROM AUTHOR]

L. plantarum at the respiratory mucosa mediates cross‐protection against lethal virus‐induced inflammation, but does not sustain survival in the absence of endogenous virus clearance mechanisms. Administration of immunobiotic Lactobacillus plantarum (Lp) directly to the respiratory mucosa promotes cross‐protection against lethal pneumovirus infection via B‐cell‐independent mechanisms. In this study, we examined Lp‐mediated cross protection in Rag1−/− mice which cannot clear virus from lung tissue. Although Lp was initially protective, Rag1−/− mice ultimately succumbed to a delayed lethal outcome associated with local production of the proinflammatory cytokines CCL1, ‐2, and ‐7, granulocyte recruitment, and ongoing virus replication. By contrast, CD8null mice, which are fully capable of clearing virus, are protected by Lp with no delayed lethal outcome, granulocyte recruitment to the airways, or induction of CCL7. Repeated administration of Lp to virus‐infected Rag1−/− mice had no impact on delayed mortality. Moreover, administration of Lp to the respiratory mucosa resulted in no induction of IFN‐α or ‐β in Rag1−/− or wild‐type mice, and IFN‐abR gene deletion had no impact on Lp‐mediated protection. Overall, our findings indicate that although Lp administered to the respiratory tract has substantial impact on lethal virus‐induced inflammation in situ, endogenous virus clearance mechanisms are needed to promote sustained protection. Our results suggest that a larger understanding of the mechanisms and mediators that limit acute virus‐induced inflammation may yield new and useful therapeutic modalities. [ABSTRACT FROM AUTHOR]