Running With Scissors: Evolutionary Conflicts Between Viral Proteases and the Host Immune System.

Many pathogens encode proteases that serve to antagonize the host immune system. In particular, viruses with a positive-sense single-stranded RNA genome [(+)ssRNA], including picornaviruses, flaviviruses, and coronaviruses, encode proteases that are not only required for processing viral polyproteins into functional units but also manipulate crucial host cellular processes through their proteolytic activity. Because these proteases must cleave numerous polyprotein sites as well as diverse host targets, evolution of these viral proteases is expected to be highly constrained. However, despite this strong evolutionary constraint, mounting evidence suggests that viral proteases such as picornavirus 3C, flavivirus NS3, and coronavirus 3CL, are engaged in molecular 'arms races' with their targeted host factors, resulting in host- and virus-specific determinants of protease cleavage. In cases where protease-mediated cleavage results in host immune inactivation, recurrent host gene evolution can result in avoidance of cleavage by viral proteases. In other cases, such as recently described examples in NLRP1 and CARD8, hosts have evolved 'tripwire' sequences that mimic protease cleavage sites and activate an immune response upon cleavage. In both cases, host evolution may be responsible for driving viral protease evolution, helping explain why viral proteases and polyprotein sites are divergent among related viruses despite such strong evolutionary constraint. Importantly, these evolutionary conflicts result in diverse protease-host interactions even within closely related host and viral species, thereby contributing to host range, zoonotic potential, and pathogenicity of viral infection. Such examples highlight the importance of examining viral protease-host interactions through an evolutionary lens.

Toward a humanized mouse model of Pneumocystis pneumonia.

Pneumocystis is an important opportunistic fungus that causes pneumonia in children and immunocompromised individuals. Recent genomic data show that divergence of major surface glycoproteins may confer speciation and host range selectivity. On the other hand, immune clearance between mice and humans is well correlated. Thus, we hypothesized that humanize mice may provide information about human immune responses involved in controlling Pneumocystis infection. CD34-engrafted huNOG-EXL mice controlled fungal burdens to a greater extent than nonengrafted mice. Moreover, engrafted mice generated fungal-specific IgM. Fungal control was associated with a transcriptional signature that was enriched for genes associated with nonopsonic recognition of trophs (CD209) and asci (CLEC7A). These same genes were downregulated in CD4-deficient mice as well as twins with bare lymphocyte syndrome with Pneumocystis pneumonia.

Interaction Differences of the Avian Host-Specific Salmonella enterica Serovar Gallinarum, the Host-Generalist S. Typhimurium, and the Cattle Host-Adapted S. Dublin with Chicken Primary Macrophage.

Most Salmonella serovars cause disease in many host species, while a few serovars have evolved to be host specific. Very little is known about the mechanisms that contribute to Salmonella host specificity. We compared the interactions between chicken primary macrophages (CDPM) and host-generalist serovar Salmonella enterica serovar Typhimurium, host-adapted Salmonella enterica serovar Dublin, and avian host-specific Salmonella enterica serovar Gallinarum. S Gallinarum was taken up in lower numbers by CDPM than S Typhimurium and S Dublin; however, a higher survival rate was observed for this serovar. In addition, S Typhimurium and S Dublin caused substantially higher levels of cell death to the CDPM, while significantly higher concentrations of NO were produced by S Gallinarum-infected cells. Global transcriptome analysis performed 2 h postinfection showed that S Gallinarum infection triggered a more comprehensive response in CDPM with 1,114 differentially expressed genes (DEGs) compared to the responses of S Typhimurium (625 DEGs) and S Dublin (656 DEGs). Comparable levels of proinflammation responses were observed in CDPM infected by these three different serovars at the initial infection phase, but a substantially quicker reduction in levels of interleukin-1ß (IL-1ß), CXCLi1, and CXCLi2 gene expression was detected in the S Gallinarum-infected macrophages than that of two other groups as infections proceeded. KEGG cluster analysis for unique DEGs after S Gallinarum infection showed that the JAK-STAT signaling pathway was top enriched, indicating a specific role for this pathway in response to S Gallinarum infection of CDPM. Together, these findings provide new insights into the interaction between Salmonella and the host and increase our understanding of S Gallinarum host specificity.

The in vitro host cell immune response to bovine-adapted Staphylococcus aureus varies according to bacterial lineage.

Mastitis is the most economically important disease affecting dairy cattle worldwide. Staphylococcus aureus is a highly prevalent cause of mastitis, causing infections ranging from sub-clinical to gangrenous. However, the interaction between the genotype of the infecting strain of S. aureus and the host response remains largely uncharacterised. To better understand the variation in presentation and outcomes of S. aureus-mediated bovine mastitis, we studied the interaction of a panel of mastitis isolates from several prominent bovine-associated lineages with bovine mammary epithelial cells (bMEC) and neutrophils. Significant differences in immune gene expression by infected primary or immortalised bMEC, or their elaboration of neutrophil chemoattractants, were observed and were dependent on the lineage of the infecting strain. Differences were also apparent in the invasiveness of S. aureus strains and their ability to survive killing by neutrophils. Our results demonstrate that a range of immune responses occur, suggesting the importance of S. aureus strain in dictating mastitis disease course. S. aureus lineages may therefore have adopted differing strategies for exploitation of the intramammary niche. Consequently, improved diagnosis of infecting lineage may enable better prognosis for S. aureus mastitis and reduce morbidity and economic loss.

[Population genetics and human immunity: the interferon paradigm]. / Génétique des populations et immunité chez l'homme - Le cas des interférons.

The evolutionary genetics dissection of immunity-related genes provides insights into immunological defence mechanisms and highlight host pathways playing an important role in pathogen resistance. Recent population genetic data have increased knowledge of the biological relevance of human interferons (IFN), cytokines released by host cells in response to pathogen presence or tumour cells. Some IFN-α subtypes as well as IFN-γ are strongly evolutionarily constrained, suggesting that the functions they fulfil are essential and non redundant. Other IFN, the most extreme cases being IFN-α10 and IFN-ε, can accumulate missense or nonsense mutations at high population frequencies, suggesting higher redundancy. Furthermore, genetic variation at some IFN genes can be advantageous for the host and increase in frequency by positive selection. This has been shown for type III IFN, where mutations at IL28A, IL28B and IL29 have been positively selected in Europeans and Asians, most likely by increasing resistance to viral infection. This review uses the IFN paradigm to illustrate the value of the evolutionary approach in highlighting important determinants of host immune responsiveness in the natural setting.

Intramacrophage survival of uropathogenic Escherichia coli: differences between diverse clinical isolates and between mouse and human macrophages.

Uropathogenic E. coli (UPEC) are the primary cause of urinary tract infections. Recent studies have demonstrated that UPEC can invade and replicate within epithelial cells, suggesting that this bacterial pathogen may occupy an intracellular niche within the host. Given that many intracellular pathogens target macrophages, we assessed the interactions between UPEC and macrophages. Colonization of the mouse bladder by UPEC strain CFT073 resulted in increased expression of myeloid-restricted genes, consistent with the recruitment of inflammatory macrophages to the site of infection. In in vitro assays, CFT073 was able to survive within primary mouse bone marrow-derived macrophages (BMM) up to 24h post-infection. Three additional well-characterized clinical UPEC isolates associated with distinct UTI symptomatologies displayed variable long-term survival within BMM. UPEC strains UTI89 and VR50, originally isolated from patients with cystitis and asymptomatic bacteriuria respectively, showed elevated bacterial loads in BMM at 24h post-infection as compared to CFT073 and the asymptomatic bacteriuria strain 83972. These differences did not correlate with differential effects on macrophage survival or initial uptake of bacteria. E. coli UTI89 localized to a Lamp1(+) vesicular compartment within BMM. In contrast to survival within mouse BMM, intracellular bacterial loads of VR50 were low in both human monocyte-derived macrophages (HMDM) and in human T24 bladder epithelial cells. Collectively, these data suggest that some UPEC isolates may subvert macrophage anti-microbial pathways, and that host species differences may impact on intracellular UPEC survival.

Graft-versus-host disease is independent of innate signaling pathways triggered by pathogens in host hematopoietic cells.

Graft-versus-host disease (GVHD) is initiated by APCs that prime alloreactive donor T cells. In antipathogen responses, Ag-bearing APCs receive signals through pattern-recognition receptors, including TLRs, which induce the expression of costimulatory molecules and production of inflammatory cytokines, which in turn mold the adaptive T cell response. However, in allogeneic hematopoietic stem cell transplantation (alloSCT), there is no specific pathogen, alloantigen is ubiquitous, and signals that induce APC maturation are undefined. To investigate APC activation in GVHD, we used recipient mice with hematopoietic cells genetically deficient in pathways critical for APC maturation in models in which host APCs are absolutely required. Strikingly, CD8-mediated and CD4-mediated GVHD were similar whether host APCs were wild-type or deficient in MyD88, TRIF, or MyD88 and TRIF, which excludes essential roles for TLRs and IL-1ß, the key product of inflammasome activation. Th1 differentiation was if anything augmented when APCs were MyD88/TRIF(-/-), and T cell production of IFN-γ did not require host IL-12. GVHD was also intact when APCs lacked the type I IFNR, which amplifies APC activation pathways that induce type I IFNs. Thus in GVHD, alloreactive T cells can be activated when pathways critical for antipathogen T cell responses are impaired.

Improving posttransplantation survival of human ovarian tissue by treating the host and graft.

OBJECTIVE: To improve posttransplantation survival of frozen-thawed human ovarian tissue in immunodeficient mice. DESIGN: Histologic study of transplanted human ovaries after treating the host and graft. SETTING: Infertility unit, university-affiliated tertiary medical center. PATIENT(S): Ovarian tissue from six girls/women (aged 5-23 years) who had undergone ovarian laparoscopy for fertility preservation. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Thawed ovarian samples were transplanted into the back muscle of immunodeficient mice divided into four groups: A) no treatment; B) host treatment with vitamin E and gonadotropins before and after grafting; C) graft incubation with vascular endothelial growth factor A (VEGF-A) and vitamin E before transplantation; and D) host as in B, graft as in C. Ungrafted thawed samples served as control. Assessment of graft survival was conducted by follicle counts, apoptosis evaluation, immunohistochemical stainings for proliferating cell nuclear antigen (PCNA) and VEGF-A expression. RESULT(S): Only grafts incubated before transplantation (groups C and D) retained their original size. Follicle number was low in all grafts. PCNA expression was found in most grafts. Apoptosis was significantly lower in the untreated and treated grafts transplanted into treated hosts (groups B and D) than in ungrafted-thawed samples and group A grafts. All grafted groups had significantly higher expression of VEGF-A than ungrafted-thawed samples. CONCLUSION(S): Survival of transplanted human ovarian tissue may be improved by treatment of the host and graft. Further studies to evaluate treatments with a potential benefit in human ovarian autotransplantation are needed.

Alternate mechanisms of initial pattern recognition drive differential immune responses to related poxviruses.

Vaccinia immunization was pivotal to successful smallpox eradication. However, the early immune responses that distinguish poxvirus immunization from pathogenic infection remain unknown. To address this, we developed a strategy to map the activation of key signaling networks in vivo and applied this approach to define and compare the earliest signaling events elicited by immunizing (vaccinia) and lethal (ectromelia) poxvirus infections in mice. Vaccinia induced rapid TLR2-dependent responses, leading to IL-6 production, which then initiated STAT3 signaling in dendritic and T cells. In contrast, ectromelia did not induce TLR2 activation, and profound mouse strain-dependent responses were observed. In resistant C57BL/6 mice, the STAT1 and STAT3 pathways were rapidly activated, whereas in susceptible BALB/c mice, IL-6-dependent STAT3 activation did not occur. These data link early immune signaling events to infection outcome and suggest that activation of different pattern-recognition receptors early after infection may be important in determining vaccine efficacy.