Cell death triggered by Yersinia enterocolitica identifies processing of the proinflammatory signal adapter MyD88 as a general event in the execution of apoptosis.

Many pathogenic microorganisms have evolved tactics to modulate host cell death or survival pathways for establishing infection. The enteropathogenic bacterium Yersinia enterocolitica deactivates TLR-induced signaling pathways, which triggers apoptosis in macrophages. In this article, we show that Yersinia-induced apoptosis of human macrophages involves caspase-dependent cleavage of the TLR adapter protein MyD88. MyD88 was also cleaved when apoptosis was mediated by overexpression of the Toll-IL-1R domain-containing adapter inducing IFN-ß in epithelial cells. The caspase-processing site was mapped to aspartate-135 in the central region of MyD88. MyD88 is consequently split by caspases in two fragments, one harboring the death domain and the other the Toll-IL-1R domain. Caspase-3 was identified as the protease that conferred the cleavage of MyD88 in in vitro caspase assays. In line with a broad role of caspase-3 in the execution of apoptosis, the processing of MyD88 was not restricted to Yersinia infection and to proapoptotic Toll-IL-1R domain-containing adapter inducing IFN-ß signaling, but was also triggered by staurosporine treatment. The cleavage of MyD88 therefore seems to be a common event in the advanced stages of apoptosis, when caspase-3 is active. We propose that the processing of MyD88 disrupts its scaffolding function and uncouples the activation of TLR and IL-1Rs from the initiation of proinflammatory signaling events. The disruption of MyD88 may consequently render dying cells less sensitive to proinflammatory stimuli in the execution phase of apoptosis. The cleavage of MyD88 could therefore be a means of conferring immunogenic tolerance to apoptotic cells to ensure silent, noninflammatory cell demise.

Altered Ig hypermutation pattern and frequency in complementary mouse models of DNA polymerase ζ activity.

To test the hypothesis that DNA polymerase ζ participates in Ig hypermutation, we generated two mouse models of Pol ζ function: a B cell-specific conditional knockout and a knock-in strain with a Pol ζ mutagenesis-enhancing mutation. Pol ζ-deficient B cells had a reduction in mutation frequency at Ig loci in the spleen and in Peyer's patches, whereas knock-in mice with a mutagenic Pol ζ displayed a marked increase in mutation frequency in Peyer's patches, revealing a pattern that was similar to mutations in yeast strains with a homologous mutation in the gene encoding the catalytic subunit of Pol ζ. Combined, these data are best explained by a direct role for DNA polymerase ζ in Ig hypermutation.

Ex vivo comparative immunogenicity assessment (EVCIA) to determine relative immunogenicity in chronic plaque psoriasis in participants receiving Humira® or undergoing repeated switches between Humira® and AVT02.

Immunogenicity against biologic medicines is ubiquitous, and it is traditionally measured by the final humoral response. However, the onset of a sustained immunogenic response begins at the cellular level with activation of T cells and maturation of naïve B cells into plasma cells. Ex vivo comparative immunogenicity assessment (EVCIA) of cellular immunogenicity in participants with moderate-to-severe chronic plaque psoriasis in the AVT02-GL-302 study, who received either reference product (RP) alone (non-switching arm) or switched between RP and AVT02 (switching arm) after 1:1 randomization at week 12. Peripheral blood mononuclear cells (PBMCs) were collected and cryopreserved from 28 participants at: baseline (before treatment) (week 1); pre-randomization (week 12); and week 16 and week 28 in both switching and non-switching arms. PBMCs were thawed and re-exposed to either medium alone (negative control), RP, AVT02, keyhole limpet hemocyanin (KLH) (positive control), RP+KLH, or AVT02+KLH. Samples from 10 participants (predetermined average cell viability of 75% across all timepoints) from each arm were analyzed for cytokine release after 24 hours and for Th-cell proliferation, 6 days post-seeding. Until week 28, cytokine release and Th-cell proliferation was similar at all time points in both switching and non-switching arms. Overall cellular immune response was elevated post-KLH re-exposure at all timepoints. The comparable ex vivo cellular immunogenicity between switching and non-switching arms complements the confirmation of interchangeability in the main study. Given the sensitivity of novel EVCIA, detecting cellular immunogenicity could be a potential outcome in predicting the immunogenicity of biologic medicines.

Altered pattern of immunoglobulin hypermutation in mice deficient in Slip-GC protein.

We recently identified a novel germinal center GTPase, SLIP-GC, that localizes to replication factories in B cells and that, when reduced, induces DNA breaks in lymphoma B cell lines in an activation-induced deaminase (AID)-dependent manner. Herein, we generated mice deficient in SLIP-GC and examined the impact of SLIP-GC deficiency in immunoglobulin hypermutation and class switch recombination, both AID-dependent mechanisms. SLIP-GC-deficient mice experienced a substantial increase in mutations at G:C base pairs at the region downstream of JH4 in the immunoglobulin heavy chain locus. This change was reflected in the overall mutation frequency, and it was associated with an increase in transitions from G:C base pairs, a hallmark of AID-mediated deamination during replication. In addition, G:C transitions at non-immunoglobulin loci also increased in these mice. Given the intracellular localization of SLIP-GC to sites of replicating DNA, these results suggest that SLIP-GC protects replicating DNA from AID-mediated deamination of cytosines in both strands.

Implementation and Routinization of the ABCDE Bundle: A Mixed Methods Evaluation.

BACKGROUND: The ABCDE (Awakening and Breathing Coordination, Delirium monitoring and management, and Early exercise/mobility) bundle has been associated with reductions in delirium incidence and improved patient outcomes but has not been widely adopted. OBJECTIVE: The objective of this study was to determine how to facilitate ABCDE bundle adoption by examining the impact of different implementation strategies on bundle adherence rates and assessing clinicians' perceptions of the bundle and implementation efforts. METHODS: This study examined the effect of 2 bundle implementation strategies on patient care in 8 adult intensive care units. The basic strategy included electronic health record (EHR) modification, whereas the enhanced strategy included EHR modification plus additional bundle training, clinical champions, and staff engagement. A total of 84 nurses, physicians, and therapists participated in interviews and a survey to assess bundle implementation. RESULTS: Respondents indicated bundle use resulted in "best care" through care standardization and coordination and improved patient outcomes. Intensive care units in both intervention groups had significant improvements in bundle adherence after implementation efforts, but intensive care units in the basic intervention group outperformed other sites after initiating their own implementation strategies. Successful implementation tactics included incorporating the bundle into multidisciplinary rounds and providing ongoing support, training, and routine auditing and feedback. DISCUSSION: The ABCDE bundle can improve quality of care and outcomes, and implementation can be accelerated through EHR tools, trainings, and performance feedback.

Safety and tolerability of non-neutralizing adrenomedullin antibody adrecizumab (HAM8101) in septic shock patients: the AdrenOSS-2 phase 2a biomarker-guided trial.

PURPOSE: Investigate safety and tolerability of adrecizumab, a humanized monoclonal adrenomedullin antibody, in septic shock patients with high adrenomedullin. METHODS: Phase-2a, double-blind, randomized, placebo-controlled biomarker-guided trial with a single infusion of adrecizumab (2 or 4 mg/kg b.w.) compared to placebo. Patients with adrenomedullin above 70 pg/mL, < 12 h of vasopressor start for septic shock were eligible. Randomization was 1:1:2. Primary safety (90-day mortality, treatment emergent adverse events (TEAE)) and tolerability (drug interruption, hemodynamics) endpoints were recorded. Efficacy endpoints included the Sepsis Support Index (SSI, reflecting ventilator- and shock-free days alive), change in Sequential-related Organ Failure Assessment (SOFA) and 28-day mortality. RESULTS: 301 patients were enrolled (median time of 8.5 h after vasopressor start). Adrecizumab was well tolerated (one interruption, no hemodynamic alteration) with no differences in frequency and severity in TEAEs between treatment arms (TEAE of grade 3 or higher: 70.5% in the adrecizumab group and 71.1% in the placebo group) nor in 90-day mortality. Difference in change in SSI between adrecizumab and placebo was 0.72 (CI -1.93-0.49, p = 0.24). Among various secondary endpoints, delta SOFA score (defined as maximum versus minimum SOFA) was more pronounced in the adrecizumab combined group compared to placebo [difference at 0.76 (95% CI 0.18-1.35); p = 0.007]. 28-day mortality in the adrecizumab group was 23.9% and 27.7% in placebo with a hazard ratio of 0.84 (95% confidence interval 0.53-1.31, log-rank p = 0.44). CONCLUSIONS: Overall, we successfully completed a randomized trial evaluating selecting patients for enrolment who had a disease-related biomarker. There were no overt signals of harm with using two doses of the adrenomedullin antibody adrecizumab; however, further randomized controlled trials are required to confirm efficacy and safety of this agent in septic shock patients.

Speckled-like pattern in the germinal center (SLIP-GC), a nuclear GTPase expressed in activation-induced deaminase-expressing lymphomas and germinal center B cells.

We identified a novel GTPase, SLIP-GC, with expression limited to a few tissues, in particular germinal center B cells. It lacks homology to any known proteins, indicating that it may belong to a novel family of GTPases. SLIP-GC is expressed in germinal center B cells and in lymphomas derived from germinal center B cells such as large diffuse B cell lymphomas. In cell lines, SLIP-GC is expressed in lymphomas that express activation-induced deaminase (AID) and that likely undergo somatic hypermutation. SLIP-GC is a nuclear protein, and it localizes to replication factories. Reduction of SLIP-GC levels in the Burkitt lymphoma cell line Raji and in non-Hodgkin lymphoma cell lines resulted in an increase in DNA breaks and apoptosis that was AID-dependent, as simultaneous reduction of AID abrogated the deleterious effects of SLIP-GC reduction. These results strongly suggest that SLIP-GC is a replication-related protein in germinal center B cells whose reduction is toxic to cells through an AID-dependent mechanism.

Differential regulation of interleukin-1 receptor associated kinase 1 (IRAK1) splice variants.

IRAK family proteins play critical roles in regulating innate immunity. There are three differentially spliced variants of IRAK1, namely 1, 1b, and 1c. We and others have previously identified that the full length IRAK1 underwent covalent modifications such as phosphorylation and ubiquitination upon lipopolysaccharide challenge. In this report, we observed that IRAK1 could also undergo sumoylation which was responsible for its translocation into the nucleus. In contrast, IRAK1c remained stable and did not undergo modification upon various challenges. Furthermore, we showed that IRAK1c solely localized in the cytoplasm. IRAK1 was absent and IRAK1c was the primary form in human brains. The absence of full length IRAK1 and presence of IRAK1c may keep brain tissue in a resting non-inflammatory state. Intriguingly, the full length IRAK1 form was consistently detected in brain tissues obtained from aged humans, suggesting that differential splicing of IRAK1 may correlate with the aging process.

High-volume hospitals are associated with lower mortality among high-risk emergency general surgery patients.

INTRODUCTION: We have previously demonstrated that Emergency General Surgery (EGS) patients treated at high-volume hospitals experience lower mortality rates than those treated at low-volume hospitals. However, EGS comprises a wide spectrum of diseases. Our goal was to determine which EGS diseases had better outcomes at high-volume hospitals. METHODS: We undertook a retrospective analysis of the National Inpatient Sample database for 2013 (a nationwide representative sample). Patients with EGS diseases were identified using American Association for the Surgery of Trauma definitions. A hierarchical logistic regression model was used to measure risk-adjusted probability of death, adjusting for age, sex, race, ethnicity, insurance type, and comorbidities. Patients were then grouped into 16 risk groups based upon their predicted probability of death. We then compared observed mortality rates at high- versus low-volume hospitals within each risk group. RESULTS: Nationwide, 3,006,615 patients with EGS diseases were treated at 4,083 hospitals in 2013. Patients with predicted risk of death of 4% or higher (275,615 patients, 9.2%) had lower observed mortality rates at high-volume hospitals than at low-volume hospitals (7.7% vs. 10.2%, p < 0.001). We estimated that 1,002 deaths were potentially preventable if high-risk patients who were treated at low-volume hospitals were instead transferred to high-volume hospitals. CONCLUSION: EGS patients with predicted risk of death of 4% or higher experience lower mortality rates at high-volume hospitals than at low-volume hospitals. A regional system of EGS care that enables rapid transfer of high-risk patients to high-volume hospitals may prevent several deaths. LEVEL OF EVIDENCE: Prognostic and epidemiological, level III; Therapeutic/Case Management, level IV.

Virtual reality and brain computer interface in neurorehabilitation.

The potential benefit of technology to enhance recovery after central nervous system injuries is an area of increasing interest and exploration. The primary emphasis to date has been motor recovery/augmentation and communication. This paper introduces two original studies to demonstrate how advanced technology may be integrated into subacute rehabilitation. The first study addresses the feasibility of brain computer interface with patients on an inpatient spinal cord injury unit. The second study explores the validity of two virtual environments with acquired brain injury as part of an intensive outpatient neurorehabilitation program. These preliminary studies support the feasibility of advanced technologies in the subacute stage of neurorehabilitation. These modalities were well tolerated by participants and could be incorporated into patients' inpatient and outpatient rehabilitation regimens without schedule disruptions. This paper expands the limited literature base regarding the use of advanced technologies in the early stages of recovery for neurorehabilitation populations and speaks favorably to the potential integration of brain computer interface and virtual reality technologies as part of a multidisciplinary treatment program.

Cost-Effectiveness of Surgical Treatment for Adult Spinal Deformity: A Comparison of Dollars per Quality of Life Improvement Across Health Domains.

DESIGN: Retrospective, single-center analysis of consecutive patients undergoing surgical treatment for adult spinal deformity (ASD). OBJECTIVE: Assess the value of surgical treatment for ASD across different health domains. SUMMARY OF BACKGROUND DATA: The cost of improvement in health-related quality of life (HRQOL) is an important consideration for resource allocation. There is also growing concern among policy makers regarding the incorporation of patient-specific preferences in the appropriate definition and assessment health care value. METHODS: Single-center, retrospective study of consecutive ASD patients undergoing primary surgery with principal diagnosis code 737.0-737.9 from 2005 through May 2010. Patients less than 18 years of age were excluded. The HRQOL measures were based on the Short Form-36, the Oswestry Disability Index (ODI), and the Scoliosis Research Society (SRS)-22 questionnaire after at least 2 years after surgery. The SRS scores were translated to a 100-point scale. Costs were collected from hospital data on the total costs incurred for the episode of surgical care. Confidence intervals were calculated using nonparametric bootstrap methods. RESULTS: Baseline and minimum 2-year HR follow-up data were available for 164 patients, with an average follow-up of 3.2 years and a range of 2 to 7.4 years. Patients were predominantly female (14; 88%) and ranged from 18 to 82 years of age at index surgery (average of 51 years of age). The cost-effectiveness (CE) ratios varied across different HRQOL outcomes, ranging from an average cost of $5,658 per 1-point improvement in SRS Self-image to an average cost of $25,918 per 1-point improvement in SF-36 Physical Component Score (PCS). Results revealed statistically significant differences (p < .05) in CE ratios across different HRQOL outcomes. CONCLUSIONS: Statistically significant differences were found in CE ratios across HRQOL sub-domains. This has important implications in the assessment of patient-specific value of health care services, and illustrates that surgical treatment for ASD may be more cost-effective for some purposes (eg, pain reduction) and less cost-effective for others (eg, improved functional activity).

Analysis of the direct cost of surgery for four diagnostic categories of adult spinal deformity.

BACKGROUND CONTEXT: Existing literature on adult spinal deformity (ASD) offers little guidance regarding an evidence-based approach to care. To optimize the value of medical treatment, a thorough understanding of the cost of surgical treatment for ASD is required. PURPOSE: To evaluate four clinically and radiographically distinct groups of ASD and identify and compare the cost of surgical treatment among the groups. STUDY DESIGN/SETTING: Multicenter retrospective study of consecutive surgeries for ASD. PATIENT SAMPLE: Three hundred twenty-five consecutive ASD patients treated between 2008 and 2010. OUTCOME MEASURES: Cost data were collected from hospital administrative records on the direct costs (DCs) incurred for the episode of surgical care, excluding overhead. METHODS: Based on preoperative radiographs and history, patients were categorized into one of four diagnostic categories of deformity: primary idiopathic scoliosis (PIS), primary degenerative scoliosis (PDS), primary sagittal plane deformity (PSPD), and revision (R). Analysis of variance and generalized linear model regressions were used to analyze the DCs of surgery and to assess differences in costs across the four diagnostic categories considered. RESULTS: Significant differences were observed in DC of surgery for different categories of ASD, with surgical treatment for PDS the most expensive followed in decreasing order by PSPD, PIS, and R (p<.01). Results further revealed a significant positive relationship between age and DC (p<.01) and a significant positive relationship between length of stay and DC (p<.01). Among PIS patients, for every incremental increase in levels fused, the expected DC increased by $3,997 (p=.00). Fusion to pelvis also significantly increased the DC of surgery for patients aged 18 to 29 years (p<.01) and 30 to 59 years (p<.01) but not for 60 years or more (p=.86). CONCLUSIONS: There is an increasing DC of surgery with increasing age, length of hospital stay, length of fusion, and fusions to the pelvis. Revision surgery is the least expensive surgery on average and should therefore not preclude its consideration from a pure cost perspective.

Journey to no preventable risk: the Baylor Health Care System patient safety experience.

The patient safety vision at Baylor Health Care System (BHCS) has 3 components: (1) achieving no preventable deaths, (2) ensuring no preventable injuries, and (3) seeking no preventable risk. These goals require strategic efforts in the categories of culture, processes, and technology. Culture focuses on tactics such as teamwork training and quality improvement education. Processes are measured using the percentage adoption of a variety of target clinical processes such as order set use and adherence to National Patient Safety Goals. Technology includes focus areas such as clinical decision support and reliability of the electronic health record. BHCS has also achieved significant systemwide standardization of safety processes and development of the systemwide Office of Patient Safety to facilitate the implementation of evidence-based patient safety practices. Associated with these improvements, BHCS has made significant progress toward reducing hospital-standardized mortality rates and rates of hospital-acquired adverse events.

Linking joint commission inpatient core measures and national patient safety goals with evidence.

As an initiative of Baylor Health Care System's Best Care Committee, we summarized the association between the Joint Commission's hospital core measures/safety goals and patient outcomes. This summary (which will be formatted as a small, laminated card) can be used by change leaders to communicate the relevance of clinical quality goals. By disseminating this evidence broadly, we aim to further invest clinical staff in delivery of specific care processes, maximize care efforts related to core measures, and extend quality improvement efforts within our organization.

Reduction of 30-day postdischarge hospital readmission or emergency department (ED) visit rates in high-risk elderly medical patients through delivery of a targeted care bundle.

RATIONALE: Care coordination has shown inconsistent results as a mechanism to reduce hospital readmission and postdischarge emergency department (ED) visit rates. OBJECTIVE: To assess the impact of a supplemental care bundle targeting high-risk elderly inpatients implemented by hospital-based staff compared to usual care on a composite outcome of hospital readmission and/or ED visitation at 30 and 60 days following discharge. PATIENTS/METHODS: Randomized controlled pilot study in 41 medical inpatients predisposed to unplanned readmission or postdischarge ED visitation, conducted at Baylor University Medical Center. The intervention group care bundle consisted of medication counseling/reconciliation by a clinical pharmacist (CP), condition specific education/enhanced discharge planning by a care coordinator (CC), and phone follow-up. RESULTS: Groups had similar baseline characteristics. Intervention group readmission/ED visit rates were reduced at 30 days compared to the control group (10.0% versus 38.1%, P = 0.04), but not at 60 days (30.0% versus 42.9%, P = 0.52). For those patients who had a readmission/postdischarge ED visit, the time interval to this event was longer in the intervention group compared to usual care (36.2 versus 15.7 days, P = 0.05). Study power was insufficient to reliably compare the effects of the intervention on lengths of index hospital stay between groups. CONCLUSIONS: A targeted care bundle delivered to high-risk elderly inpatients decreased unplanned acute health care utilization up to 30 days following discharge. Dissipation of this effect by 60 days postdischarge defines reasonable expectations for analogous hospital-based educational interventions. Further research is needed regarding the impacts of similar care bundles in larger populations across a variety of inpatient settings.

Catalytically active Yersinia outer protein P induces cleavage of RIP and caspase-8 at the level of the DISC independently of death receptors in dendritic cells.

Yersinia outer protein P (YopP) is injected by Y. enterocolitica into host cells thereby inducing apoptotic and necrosis-like cell death in dendritic cells (DC). Here we show the pathways involved in DC death caused by the catalytic activity of YopP. Infection with Yersinia enterocolitica, translocating catalytically active YopP into DC, triggered procaspase-8 cleavage and c-FLIPL degradation. YopP-dependent caspase-8 activation was, however, not mediated by tumor necrosis factor (TNF) receptor family members since the expression of both CD95/Fas/APO-1 and TRAIL-R2 on DC was low, and DC were resistant to apoptosis induced by agonistic anti-CD95 antibodies or TNF-related apoptosis-inducing ligand (TRAIL). Moreover, DC from TNF-Rp55-/- mice were not protected against YopP-induced cell death demonstrating that TNF-R1 is also not involved in this process. Activation of caspase-8 was further investigated by coimmunoprecitation of FADD from Yersinia-infected DC. We found that both cleaved caspase-8 and receptor interacting protein 1 (RIP1) were associated with the Fas-associated death domain (FADD) indicating the formation of an atypical death-inducing signaling complex (DISC). Furthermore, degradation of RIP mediated by the Hsp90 inhibitor geldanamycin significantly impaired YopP-induced cell death. Altogether our findings indicate that Yersinia-induced DC death is independent of death domain containing receptors, but mediated by RIP and caspase-8 at the level of DISC.

The proteasome pathway destabilizes Yersinia outer protein E and represses its antihost cell activities.

Pathogenic Yersinia spp. neutralize host defense mechanisms by engaging a type III protein secretion system that translocates several Yersinia outer proteins (Yops) into the host cell. Although the modulation of the cellular responses by individual Yops has been intensively studied, little is known about the fate of the translocated Yops inside the cell. In this study, we investigated involvement of the proteasome, the major nonlysosomal proteolytic system in eukaryotic cells, in Yop destabilization and repression. Our data show that inhibition of the proteasome in Yersinia enterocolitica-infected cells selectively stabilized the level of YopE, but not of YopH or YopP. In addition, YopE was found to be modified by ubiquitination. This suggests that the cytotoxin YopE is physiologically subjected to degradation via the ubiquitin-proteasome pathway inside the host cell. Importantly, the increased levels of YopE upon proteasome inhibition were associated with decreased activity of its cellular target Rac. Thus, the GTPase-down-regulating function of YopE is enhanced when the proteasome is inhibited. The stabilization of YopE by proteasome inhibitor treatment furthermore led to aggravation of the cytotoxic YopE effects on the actin cytoskeleton and on host cell morphology. Together, these data show that the host cell proteasome functions to destabilize and inactivate the Yersinia effector protein YopE. This implies the proteasome as integral part of the cellular host immune response against the immunomodulatory activities of a translocated bacterial virulence protein.

Yersinia outer protein P suppresses TGF-beta-activated kinase-1 activity to impair innate immune signaling in Yersinia enterocolitica-infected cells.

Pathogenic Yersinia spp. use a panel of virulence proteins that antagonize signal transduction processes in infected cells to undermine host defense mechanisms. One of these proteins, Yersinia enterocolitica outer protein P (YopP), down-regulates the NF-kappaB and MAPK signaling pathways, which suppresses the proinflammatory host immune response. In this study, we explored the mechanism by which YopP succeeds to simultaneously disrupt several of these key signaling pathways of innate immunity. Our data show that YopP operates upstream of its characterized eukaryotic binding partner IkappaB kinase-beta to shut down the NF-kappaB signaling cascade. Accordingly, YopP efficiently impaired the activities of TGF-beta-activated kinase-1 (TAK1) in infected cells. TAK1 is an important activator of the IkappaB kinase complex in the TLR signaling cascade. The repression of TAK1 activities correlated with reduced activation of NF-kappaB- as well as AP-1-dependent reporter gene expression in Yersinia-infected murine macrophages. This suggests that the impairment of the TAK1 enzymatic activities by Yersinia critically contributes to down-regulate activation of NF-kappaB and of MAPK members in infected host cells. The inhibition of TAK1 potentially results from the blockade of signaling events that control TAK1 induction. This process could involve the attenuation of ubiquitination of the upstream signal transmitter TNFR-associated factor-6. Together, these results indicate that, by silencing the TAK1 signaling complex, Yersinia counteracts the induction of several conserved signaling pathways of innate immunity, which aids the bacterium in subverting the host immune response.

Lipopolysaccharide desensitization of macrophages provides protection against Yersinia enterocolitica-induced apoptosis.

Pathogenic Yersinia spp. uncouple an array of signal transduction pathways in macrophages to disrupt their response to infection. This compels the macrophage to undergo apoptosis. Our study shows that macrophages that had acquired tolerance to Yersinia infection by preexposure to lipopolysaccharide were considerably protected against Y. enterocolitica-induced apoptosis. The desensitization of macrophages by lipopolysaccharide, which is thought to be a self-protective, adaptive response to sustained bacterial stimulation, may represent an immune mechanism that aids in overcoming Yersinia-mediated apoptosis and infection.