Dermatological manifestations of tick-borne viral infections found in the United States.

Tick-borne diseases (TBDs) are bacterial, viral, and parasitic diseases transmitted by ticks. Viral TBDs have increased in prevalence over the last decade with many new pathogenic viruses being discovered. Doxycycline is often empirically prescribed by clinicians to treat symptomatic patients following tick bites due to suspicions of bacterial TBDs such as Rocky Mountain spotted fever, anaplasmosis, and ehrlichiosis. However, viral TBDs are included in the differential diagnosis if patients do not clinically improve following antibiotic therapy. Several viral TBDs present with dermatological manifestations. Recognizing the differences in clinical presentations of TBDs, particularly of newly emerging viral TBDs in the United States, can help physicians identify the viral TBD, and possibly rule out viral illnesses with different clinical presentations. Therefore, this review discusses clinical manifestations, with an emphasis on dermatologic manifestations of Heartland Virus, Bourbon Virus, Powassan Virus, Deer Tick Virus and Colorado Tick Fever Virus. KEY POINTS: Viral tick-borne diseases have increased in prevalence over the last decade and often have similar clinical manifestations to other tick-borne diseases, including bacterial infections. Here, we review the dermatologic manifestations of Heartland Virus (HRTV), Bourbon Virus (BRBV), Powassan Virus (POWV), Deer Tick Virus (DTV) and Colorado Tick Fever Virus (CTFV) that are important for clinicians.

Molecular Detection of Rickettsia felis in Fleas of Companion Animals in East Texas.

Flea-borne spotted fever is an emerging insect-borne rickettsial infection caused by Rickettsia felis and has been identified worldwide. This study sought to explore the prevalence of rickettsiae associated with fleas on companion dogs and cats from Walker and Montgomery Counties in East Texas. Fleas were collected from animals entering local veterinary clinics for routine checkups. Collected fleas were identified as Ctenocephalides felis or Pulex irritans and analyzed by polymerase chain reaction for the presence of rickettsiae and subsequent sequencing. An estimation of the bcMLE (bias-corrected maximum likelihood estimation) of pooled samples was calculated. Four hundred eighty-eight fleas (comprising C. felis and P. irritans) were collected from 16 cats and 77 dogs. Our results demonstrate R. felis in 21 pools of fleas from dogs (bcMLE 15.28%) and a bcMLE of 7.25% from flea samples collected from cats. Sequence analysis revealed R. felis as the only Rickettsia that could be amplified in our samples using the rickettsial citrate synthase gene and subsequent sequencing. In this study, the presence of R. felis in fleas from companion cats and dogs suggests a potential risk of flea-borne spotted fever in humans who encounter flea-infested animals.

Testing the role of inflammation in the relation of childhood maltreatment and suicidal ideation among young adults.

BACKGROUND: In recent years, the prevalence of suicidal ideation among young adults has been on the rise, with childhood maltreatment thought to partially explain this disparity. Systemic inflammation-a product of over-activation of the body's stress response system-has been hypothesized to play a predictive role in the development of suicidal ideation. Enduring childhood maltreatment can lead to systemic inflammation, possibly accounting for suicidal ideation's increased prevalence among young adults who have a history of childhood maltreatment. METHODS: The current study sought to investigate the importance of childhood maltreatment as a static risk factor for downstream suicidal ideation in young adulthood with the immunological response (i.e., systemic inflammation) to childhood maltreatment serving as a mediating factor. RESULTS: Systemic inflammation was found to be positively associated with suicidal ideation, supporting the unique role systemic inflammation may play in the pathogenesis of suicidal ideation, though hypotheses regarding childhood maltreatment were not supported. CONCLUSION: This study provides novel insight into a potential immunobiological model for suicidal ideation development in young adult populations.

Inflammatory and environmental contributions to social information processing.

It appears that social information processing is negatively affected by inflammation, but extant research is primarily experimental and comes from laboratory-based manipulations of inflammatory states. We aimed to examine interactions between inflammation, stressful life events, and positive memories of childhood relations with parents in relation to social information processing in 201 adults. We hypothesized that increased inflammation and stressful life events would be associated with greater hostile social information processing, but that positive memories of childhood relations with parents would moderate both relations. Results indicated that high IL-6 levels and stressful life events were significantly associated with direct and hostile social information processing. Positive memories of childhood relations with parents attenuated the link between stressful life events and social information processing. Findings suggest that both immune function and environmental stressors are related to social information processing and that positive memories of childhood relations exert some buffering effect.

Age and Body Condition Influence the Post-Prandial Interleukin-1ß Response to a High-Starch Meal in Horses.

Older horses and those prone to obesity may be at a higher risk for inflammation than younger and leaner counterparts. Previous research indicated a postprandial elevation in plasma concentrations of interleukin-1ß (IL-1ß), a pro-inflammatory cytokine, after consuming 1.2 g of non-structural carbohydrates/kilogram of body weight. However, these studies utilized horses of mixed age and body condition. The current study evaluated post-prandial IL-1ß concentrations in horses specifically comparing lean to over-conditioned and middle aged to older. Our results suggest that at least two weeks of daily consumption of a high non-structural carbohydrate diet is required to induce a post-prandial increase in IL-1ß concentrations in younger and leaner horses. In opposition to this, older and over-conditioned horses experience plasma increased on the first day of feeding and thereafter. Feeding management practices of older and over-conditioned individuals should emphasize lower non-structural carbohydrate intakes and further research should elucidate mechanisms of IL-1ß activation.

Serological and Molecular Detection of Anaplasma spp. in Blood From Healthy Horses: A Preliminary Study of Horses in East Texas.

Anaplasmosis is a disease caused by the bacterium Anaplasma phagocytophilum, which is spread by infected ticks. In horses, A. phagocytophilum generally causes transient infection characterized by fever, lethargy, inappetence, ventral edema, petechiae, icterus, ataxia, recumbency, muscle stiffness, and, in severe cases, death. Following natural infection, horses retain antibodies for approximately 2 years, which can be detected through an immunofluorescence antibody assay. Current infections are determined through PCR assay of white blood cell DNA. For this study, whole blood was collected from apparently healthy horses located in East Texas (n = 70), west Texas (n = 3), New York (n = 49), and New Jersey (n = 11) for the determination of serum antibodies and PCR testing of bacterial DNA. Of the 133 horses, 24 tested positive for DNA presence of A. phagocytophilum, and 107 tested positive for serum antibodies. Of the 24 horses testing positive for A. phagocytophilum, 16 were positive for serum antibody presence and 8 were negative. Twenty of the msp2 positive horses were located in East Texas and 4 resided in New York. For serum antibodies, 100% of New York and New Jersey horses tested positive, while only 66% of Texas horses tested positive. This study provides evidence that a large number of horses are exposed to A. phagocytophilum and that this bacterium is present in East Texas. No Texas horse owners reported treatment for anaplasmosis, and the currently infected horses were not demonstrating signs of illness at the time of sample collection. Further research to understand the differences in disease severity amongst equine populations is warranted.

Colorado tick fever virus induces apoptosis in human endothelial cells to facilitate viral replication.

Colorado tick fever virus (CTFV) belongs to the genus Coltivirus of the Reoviridae family, and it is the causative agent of Colorado tick fever. Symptoms of the infection are characterized by sudden biphasic fever, headache, and petechial rash, while severe forms of the disease can include meningoencephalitis, hemorrhagic fever, and death in children. However, the mechanisms underlying CTFV induced pathology and severe complications remain unknown. As CTFV is spread by tick bites and disseminates systemically via hematogenous routes, we performed in vitro analysis examining the interactions between endothelial cells (ECs) and CTFV. Our findings indicate that dermal microvascular ECs, HMEC-1, are susceptible and permissive to CTFV infection. To investigate the role of CTFV infection on endothelial barrier function, we assessed transendothelial electrical resistance (TEER) by xCELLigence and observed a dose-dependent decrease in cell index, indicating increased vascular permeability starting at approximately hour 18 (MOI=1) and hour 26 (MOI=0.1). Since CTFV induced cytopathic effect and increased vascular permeability in HMEC-1 cells, we hypothesized that CTFV causes apoptotic cell death. Our results showed that HMEC-1 cells infected with CTFV at 48 h caused a significant increase in Annexin V staining with reduced viability compared to uninfected cells suggesting CTFV induces apoptotic cell death in human ECs. Electron microscopy also was consistent with apoptotic features, including chromatin condensation and cell blebbing. Furthermore, CTFV induced caspase-3/7 activation at 24 and 48 h post-infection (hpi). The inhibition of caspase activity using Z-VAD-FMK reduced CTFV induced cell death and significantly reduced viral titer. These results indicated that CTFV can infect ECs, exerting direct adverse effects, leading to vascular permeability and cell death. Overall, our data suggest that caspase-mediated apoptosis is a critical mechanism by which CTFV induces disease in the host and enhances viral replication. Future studies will examine the viral and cellular determinants involved in CTFV induced apoptosis in human ECs.

Subversion of Host Innate Immunity by Rickettsia australis via a Modified Autophagic Response in Macrophages.

We recently reported that the in vitro and in vivo survivals of Rickettsia australis are Atg5-dependent, in association with an inhibited level of anti-rickettsial cytokine, IL-1ß. In the present study, we sought to investigate how R. australis interacts with host innate immunity via an Atg5-dependent autophagic response. We found that the serum levels of IFN-γ and G-CSF in R. australis-infected Atg5flox/flox Lyz-Cre mice were significantly less compared to Atg5flox/flox mice, accompanied by significantly lower rickettsial loads in tissues with inflammatory cellular infiltrations including neutrophils. R. australis infection differentially regulated a significant number of genes in bone marrow-derived macrophages (BMMs) in an Atg5-depdent fashion as determined by RNA sequencing and Ingenuity Pathway Analysis, including genes in the molecular networks of IL-1 family cytokines and PI3K-Akt-mTOR. The secretion levels of inflammatory cytokines, such as IL-1α, IL-18, TNF-α, and IL-6, by R. australis-infected Atg5flox/flox Lyz-Cre BMMs were significantly greater compared to infected Atg5flox/flox BMMs. Interestingly, R. australis significantly increased the levels of phosphorylated mTOR and P70S6K at a time when the autophagic response is induced. Rapamycin treatment nearly abolished the phosphorylated mTOR and P70S6K but did not promote significant autophagic flux during R. australis infection. These results highlight that R. australis modulates an Atg5-dependent autophagic response, which is not sensitive to regulation by mTORC1 signaling in macrophages. Overall, we demonstrate that R. australis counteracts host innate immunity including IL-1ß-dependent inflammatory response to support the bacterial survival via an mTORC1-resistant autophagic response in macrophages.

COVID-19 threatens maternal mental health and infant development: possible paths from stress and isolation to adverse outcomes and a call for research and practice.

The COVID-19 pandemic exposed mothers to stress and social isolation during the pre- and post-natal periods. The deleterious effects of stress on both pregnant women and their infants are well documented, with research suggesting that effects are exacerbated by reduced social support. In this brief report, we summarize evidence linking stress and social isolation to negative outcomes for mothers and infants and present a conceptual model featuring inflammation as a driving mechanism. There is strong evidence that the coronavirus pandemic will affect mothers and infants through immune pathways that, in previous research, have been shown to link stress and social isolation during the pre- and post-natal periods with deficits in maternal mental health and infant well-being and development across developmental stages. We close with recommendations for novel research, policy changes, and integrated clinical care that can address these biological threats to infants and mothers while leveraging the anti-inflammatory effects of social support.

Non-hydrolytic synthesis of caprylate capped cobalt ferrite nanoparticles and their application against Erwinia carotovora and Stenotrophomonas maltophilia.

Magnetic cobalt Ferrite nanoparticles capped with caprylate groups, CH3(CH2)6CO2-, have been synthesized using a novel non-hydrolytic coprecipitation method under inert conditions. Particle diameter was characterized using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The spinel ferrite crystal phase was verified using X-ray diffraction (XRD), and the presence of the capping agent was confirmed using Fourier Transform Infrared spectroscopy (FTIR). Bactericidal effects of the particles were tested against broth cultures of Erwinia carotovora and Stenotrophomonas maltophilia. The final particles had an average diameter of 3.81 nm and readily responded to a neodymium magnet. The particles did have a significant effect on the OD600 of both broth cultures.

Quantitative Proteomics of the Endothelial Secretome Identifies RC0497 as Diagnostic of Acute Rickettsial Spotted Fever Infections.

Mediterranean spotted fever is a reemerging acute tick-borne infection produced by the α-proteobacterium, Rickettsia conorii. Rickettsia conorii infects vascular endothelial cells producing disseminated plasma leakage, manifesting as nonspecific fever, headache, and maculopapular rash. Because there are no available tests of early infection, Mediterranean spotted fever is often undiagnosed and untreated, resulting in significant mortality. To address this critical need, we have applied a quantitative proteomics pipeline for analyzing the secretome of primary human umbilical vein endothelial cells. Of the 104 proteins whose abundance changed significantly in the R. conorii-infected human umbilical vein endothelial cells' secretome, 46 proteins were up-regulated: 45 were host secreted proteins (including cytokines), and 1 was a rickettsial protein, the putative N-acetylmuramoyl-l-alanine amidase RC0497. Proteins with sequence highly homologous to RC0497 were found to be shared by many species of the spotted fever group rickettsiae, but not typhus group rickettsiae. Quantitative targeted proteomics studies of plasma from a mouse model of sublethal and lethal R. conorii identified RC0497 in the blood, and its circulating levels were proportionally associated with infection outcome. Finally, the presence of RC0497 in the serum samples from a cohort of humans presenting with acute rickettsioses was confirmed. The detection of RC0497 has the potential to be a sensitive and specific marker for acute rickettsial spotted rickettsioses.

Atg5 Supports Rickettsia australis Infection in Macrophages In Vitro and In Vivo.

Rickettsiae can cause life-threatening infections in humans. Macrophages are one of the initial targets for rickettsiae after inoculation by ticks. However, it remains poorly understood how rickettsiae remain free in macrophages prior to establishing their infection in microvascular endothelial cells. Here, we demonstrated that the concentration of Rickettsia australis was significantly greater in infected tissues of Atg5flox/flox mice than in the counterparts of Atg5flox/flox Lyz-Cre mice, in association with a reduced level of interleukin-1ß (IL-1ß) in serum. The greater concentration of R. australis in Atg5flox/flox bone marrow-derived macrophages (BMMs) than in Atg5flox/flox Lyz-Cre BMMs in vitro was abolished by exogenous treatment with recombinant IL-1ß. Rickettsia australis induced significantly increased levels of light chain 3 (LC3) form II (LC3-II) and LC3 puncta in Atg5-competent BMMs but not in Atg5-deficient BMMs, while no p62 turnover was observed. Further analysis found the colocalization of LC3 with a small portion of R. australis and Rickettsia-containing double-membrane-bound vacuoles in the BMMs of B6 mice. Moreover, treatment with rapamycin significantly increased the concentrations of R. australis in B6 BMMs compared to those in the untreated B6 BMM controls. Taken together, our results demonstrate that Atg5 favors R. australis infection in mouse macrophages in association with a suppressed level of IL-1ß production but not active autophagy flux. These data highlight the contribution of Atg5 in macrophages to the pathogenesis of rickettsial diseases.

Vector Tick Transmission Model of Spotted Fever Rickettsiosis.

Many aspects of rickettsial infections have been characterized, including pathogenic and immune pathways and mechanisms of rickettsial survival within the vertebrate host and tick vector. However, very few studies are focused on the complex pathogen-vector-host interactions during tick feeding. Therefore, our objective was to develop a tick transmission model of the spotted fever group of rickettsial infections to study the initial events in disease development. The most appropriate strain of mouse was identified for evaluation as a transmission model, and the course of infection, bacterial levels, histopathologic changes, and antibody response during tick transmission in mice infested with Amblyomma maculatum ticks carrying the emerging pathogen, Rickettia parkeri, were studied. Results showed distinct clinical signs in C3H/HeN mice infected intravenously, leading to selection of this mouse strain for tick transmission studies. Active infection of animals was observed after tick vector transmission. The bacteria disseminated systemically and spread to several organs at 24 hours after tick attachment, with peak bacterial load at day 6 after tick attachment. Skin, lung, and liver showed the greatest pathologic changes, with inflammatory cellular infiltration and necrosis. These findings indicate the feasibility of using murine infection with R. parkeri by A. maculatum tick transmission as a model to study different aspects of the spotted fever group of rickettsial disease establishment.

Rickettsia australis Activates Inflammasome in Human and Murine Macrophages.

Rickettsiae actively escape from vacuoles and replicate free in the cytoplasm of host cells, where inflammasomes survey the invading pathogens. In the present study, we investigated the interactions of Rickettsia australis with the inflammasome in both mouse and human macrophages. R. australis induced a significant level of IL-1ß secretion by human macrophages, which was significantly reduced upon treatment with an inhibitor of caspase-1 compared to untreated controls, suggesting caspase-1-dependent inflammasome activation. Rickettsia induced significant secretion of IL-1ß and IL-18 in vitro by infected mouse bone marrow-derived macrophages (BMMs) as early as 8-12 h post infection (p.i.) in a dose-dependent manner. Secretion of these cytokines was accompanied by cleavage of caspase-1 and was completely abrogated in BMMs deficient in caspase-1/caspase-11 or apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), suggesting that R. australis activate the ASC-dependent inflammasome. Interestingly, in response to the same quantity of rickettsiae, NLRP3-/- BMMs significantly reduced the secretion level of IL-1ß compared to wild type (WT) controls, suggesting that NLRP3 inflammasome contributes to cytosolic recognition of R. australis in vitro. Rickettsial load in spleen, but not liver and lung, of R. australis-infected NLRP3-/- mice was significantly greater compared to WT mice. These data suggest that NLRP3 inflammasome plays a role in host control of bacteria in vivo in a tissue-specific manner. Taken together, our data, for the first time, illustrate the activation of ASC-dependent inflammasome by R. australis in macrophages in which NLRP3 is involved.

MyD88 Mediates Instructive Signaling in Dendritic Cells and Protective Inflammatory Response during Rickettsial Infection.

Spotted fever group rickettsiae cause potentially life-threatening infections throughout the world. Several members of the Toll-like receptor (TLR) family are involved in host response to rickettsiae, and yet the mechanisms by which these TLRs mediate host immunity remain incompletely understood. In the present study, we found that host susceptibility of MyD88(-/-)mice to infection with Rickettsia conorii or Rickettsia australis was significantly greater than in wild-type (WT) mice, in association with severely impaired bacterial clearance in vivo R. australis-infected MyD88(-/-)mice showed significantly lower expression levels of gamma interferon (IFN-γ), interleukin-6 (IL-6), and IL-1ß, accompanied by significantly fewer inflammatory infiltrates of macrophages and neutrophils in infected tissues, than WT mice. The serum levels of IFN-γ, IL-12, IL-6, and granulocyte colony-stimulating factor were significantly reduced, while monocyte chemoattractant protein 1, macrophage inflammatory protein 1α, and RANTES were significantly increased in infected MyD88(-/-)mice compared to WT mice. Strikingly, R. australis infection was incapable of promoting increased expression of MHC-II(high)and production of IL-12p40 in MyD88(-/-)bone marrow-derived dendritic cells (BMDCs) compared to WT BMDCs, although costimulatory molecules were upregulated in both types of BMDCs. Furthermore, the secretion levels of IL-1ß by Rickettsia-infected BMDCs and in the sera of infected mice were significantly reduced in MyD88(-/-)mice compared to WT controls, suggesting that in vitro and in vivo production of IL-1ß is MyD88 dependent. Taken together, our results suggest that MyD88 signaling mediates instructive signals in DCs and secretion of IL-1ß and type 1 immune cytokines, which may account for the protective inflammatory response during rickettsial infection.

Rickettsia massiliae and Rickettsia conorii Israeli Spotted Fever Strain Differentially Regulate Endothelial Cell Responses.

Rickettsiae primarily target microvascular endothelial cells. However, it remains elusive how endothelial cell responses to rickettsiae play a role in the pathogenesis of rickettsial diseases. In the present study, we employed two rickettsial species with high sequence homology but differing virulence to investigate the pathological endothelial cell responses. Rickettsia massiliae is a newly documented human pathogen that causes a mild spotted fever rickettsiosis. The "Israeli spotted fever" strain of R. conorii (ISF) causes severe disease with a mortality rate up to 30% in hospitalized patients. At 48 hours post infection (HPI), R. conorii (ISF) induced a significant elevation of IL-8 and IL-6 while R. massiliae induced a statistically significant elevated amount of MCP-1 at both transcriptional and protein synthesis levels. Strikingly, R. conorii (ISF), but not R. massiliae, caused a significant level of cell death or injury in HMEC-1 cells at 72 HPI, demonstrated by live-dead cell staining, annexin V staining and lactate dehydrogenase release. Monolayers of endothelial cells infected with R. conorii (ISF) showed a statistically significant decrease in electrical resistance across the monolayer compared to both R. massiliae-infected and uninfected cells at 72 HPI, suggesting increased endothelial permeability. Interestingly, pharmacological inhibitors of caspase-1 significantly reduced the release of lactate dehydrogenase by R. conorii (ISF)-infected HMEC-1 cells, which suggests the role of caspase-1 in mediating the death of endothelial cells. Taken together, our data illustrated that a distinct proinflammatory cytokine profile and endothelial dysfunction, as evidenced by endothelial cell death/injury and increased permeability, are associated with the severity of rickettsial diseases.

A phase I study of decitabine and rapamycin in relapsed/refractory AML.

A phase I study utilizing decitabine (DAC) followed by the mammalian target of rapamycin (mTOR) inhibitor, rapamycin, in patients with relapsed/refractory adult AML was undertaken to assess safety and feasibility. Patients received DAC 20mg/m(2) intravenously daily for 5 days followed by rapamycin from day 6 to day 25 at doses of 2 mg, 4 mg, and 6 mg/day in a standard 3+3 dose escalation design. Twelve patients completed treatment for safety evaluation. Maximum tolerated dose (MTD) was not reached, and except for grade 3 mucositis in 4 patients, no other significant unexpected non-hematologic toxicities have occurred indicating safety of this regimen. This trial is registered at clinical trials.gov as NCT00861874.

Proteasome inhibition in myelodysplastic syndromes and acute myelogenous leukemia cell lines.

In this work, effects of bortezomib on apoptosis, clonal progenitor growth, cytokine production, and NF-κB expression in patients with MDS with cytopenias requiring transfusion support are examined. Bortezomib increased apoptosis in marrow mononuclear cells but had no effects on CFU-GM, BFU-E, or CFU-L content. No consistent effects on NF-κB activation in vivo were noted. To further define the role of bortezomib in AML and MDS, we examined it in combination with several targeted agents and chemotherapeutic agents in vitro. Combinations with arsenic trioxide, sorafenib, and cytarabine demonstrated synergistic in vitro effects in AML cell lines.

Cytotoxicity of algae extracts on normal and malignant cells.

Algae preparations are commonly used in alternative medicine. We examined the effects of algae extracts on normal hematopoietic cells and leukemia cells. Ethanol extracts were prepared of Dunaliella salina (Dun), Astaxanthin (Ast), Spirulina platensis (Spir), and Aphanizomenon flos-aquae (AFA). Cell viability effects were completed by Annexin staining. Ast and AFA inhibited HL-60 and MV-4-11 whereas Dun and Spir had no effect. Primary AML blasts demonstrated increased apoptosis in AFA. Primary CLL cells showed apoptosis at 24 hours after exposure to Dun, Ast, Spir, and AFA. High AFA concentrations decreased viability of normal marrow cells. Normal CD34+ viability was inhibited by Dun. Dun and AFA inhibited BFU-E, but all extracts inhibited CFU-GM. Cell-cycle analysis of AML cell lines showed G0/G1 arrest in the presence of AFA. These data suggest that algae extracts may inhibit AML cell lines and leukemia blasts, but they may also have potential inhibitory effects on normal hematopoiesis.

Rickettsia rickettsii infection protects human microvascular endothelial cells against staurosporine-induced apoptosis by a cIAP(2)-independent mechanism.

BACKGROUND: Manipulation of host cell death is an important determinant of the outcome of an infection. Here, we investigate whether Rickettsia rickettsii-infected host endothelial cells resist the effects of staurosporine, a potent inducer of apoptosis, and we explore the mechanisms underlying the anti-apoptotic effect of infection. METHODS: Human microvascular endothelial cells infected with R. rickettsii for 24 or 48 h were challenged with staurosporine. The extent of apoptosis was evaluated with flow cytometry. mRNA and protein expression levels were determined by use of microarray or polymerase chain reaction and immunoblotting, respectively. RESULTS: Staurosporine-induced apoptosis in endothelial cells infected for 24 and 48 h was significantly reduced, compared with simultaneously treated uninfected cells. A microarray of human genes involved in apoptosis and polymerase chain reaction analyses revealed increased steady-state mRNA expression of cIAP2 (a member of the inhibitor-of-apoptosis family of proteins) at 24 h after infection. The levels of cIAP2 protein (+/-SD) in infected cells were 3.5 +/- 1.7 -fold and 2.3 +/- 1.2 -fold higher than that in uninfected control cells at 24 and 48 h after infection. Nucleofection of human-specific cIAP2-targeted siRNA resulted in inhibition of protein expression by > or = 50% but had no effect on infection-induced protection against apoptosis. CONCLUSIONS: R. rickettsii-induced expression of cIAP2 in host endothelial cells is likely not a major contributor to protection against staurosporine-induced cell death.