TRAF7 is an essential regulator of blood vessel integrity during mouse embryonic and neonatal development.

Targeted deletion of TRAF7 revealed that it is a crucial part of shear stress-responsive MEKK3-MEK5-ERK5 signaling pathway induced in endothelial cells by blood flow. Similar to Mekk3-, Mek5- or Erk5-deficient mice, Traf7-deficient embryos died in utero around midgestation due to impaired endothelium integrity. They displayed significantly lower expression of transcription factor Klf2, an essential regulator of vascular hemodynamic forces downstream of the MEKK3-MEK-ERK5 signaling pathway. In addition, deletion of Traf7 in endothelial cells of postnatal mice was associated with severe cerebral hemorrhage. Here, we show that besides MEKK3 and MEK5, TRAF7 associates with a planar cell polarity protein SCRIB. SCRIB binds with an N-terminal region of TRAF7, while MEKK3 associates with the C-terminal WD40 domain. Downregulation of TRAF7 as well as SCRIB inhibited fluid shear stress-induced phosphorylation of ERK5 in cultured endothelial cells. These findings suggest that TRAF7 and SCRIB may comprise an upstream part of the MEKK3-MEK5-ERK5 signaling pathway.

Specific gene expression signatures of low grade meningiomas.

Introduction: Meningiomas are the most common primary central nervous system (CNS) tumors in adults, representing approximately one-third of all primary adult CNS tumors. Although several recent publications have proposed alternative grading systems of meningiomas that incorporate genomic and/or epigenomic data to better predict meningioma recurrence and progression-free survival, our understanding of driving forces of meningioma development is still limited. Objective: To define gene expression signatures of the most common subtypes of meningiomas to better understand cellular processes and signaling pathways specific for each tumor genotype. Methods: We used RNA sequencing (RNA-seq) to determine whole transcriptome profiles of twenty meningiomas with genomic alterations including NF2 inactivation, loss of chr1p, and missense mutations in TRAF7, AKT1 and KLF4. Results: The analysis revealed that meningiomas with NF2 gene inactivation expressed higher levels of BCL2 and GLI1 compared with tumors harboring TRAF7 missense mutations. Moreover, NF2 meningiomas were subdivided into two distinct groups based on additional loss of chr1p. NF2 tumors with intact chr1p were characterized by the high expression of tumor suppressor PTCH2 compared to NF2 tumors with chr1p loss. Taken together with the high expression of BCL2 and GLI1, these results suggest that activation of Sonic Hedgehog pathway may contribute to NF2 meningioma development. In contrast, NF2 tumors with chr1p loss expressed high levels of transcription factor FOXD3 and its antisense RNA FOXD3-AS1. Examination of TRAF7 tumors demonstrated that TRAF7 regulates a number of biomechanically responsive genes (KRT6a, KRT16, IL1RL1, and AQP3 among others). Interestingly, AKT1 and KLF4 meningiomas expressed genes specific for PI3K/AKT signaling pathway, suggesting overlapping gene signatures between the two subtypes. In addition, KLF4 meningiomas had high expression of carcinoembryonic antigen family members CEACAM6 and CEACAM5. Conclusions: Each group of meningiomas displayed a unique gene expression signature suggesting signaling pathways potentially implicated in tumorigenesis. These findings will improve our understanding of meningioma tumorigenesis and prognosis.

COMMD10 Is Essential for Neural Plate Development during Embryogenesis.

The COMMD (copper metabolism MURR1 domain containing) family includes ten structurally conserved proteins (COMMD1 to COMMD10) in eukaryotic multicellular organisms that are involved in a diverse array of cellular and physiological processes, including endosomal trafficking, copper homeostasis, and cholesterol metabolism, among others. To understand the role of COMMD10 in embryonic development, we used Commd10Tg(Vav1-icre)A2Kio/J mice, where the Vav1-cre transgene is integrated into an intron of the Commd10 gene, creating a functional knockout of Commd10 in homozygous mice. Breeding heterozygous mice produced no COMMD10-deficient (Commd10Null) offspring, suggesting that COMMD10 is required for embryogenesis. Analysis of Commd10Null embryos demonstrated that they displayed stalled development by embryonic day 8.5 (E8.5). Transcriptome analysis revealed that numerous neural crest-specific gene markers had lower expression in mutant versus wild-type (WT) embryos. Specifically, Commd10Null embryos displayed significantly lower expression levels of a number of transcription factors, including a major regulator of the neural crest, Sox10. Moreover, several cytokines/growth factors involved in early embryonic neurogenesis were also lower in mutant embryos. On the other hand, Commd10Null embryos demonstrated higher expression of genes involved in tissue remodeling and regression processes. Taken together, our findings show that Commd10Null embryos die by day E8.5 due to COMMD10-dependent neural crest failure, revealing a new and critical role for COMMD10 in neural development.

Mutated KLF4(K409Q) in meningioma binds STRs and activates FGF3 gene expression.

Krüppel-like factor 4 (KLF4) is a transcription factor that has been proven necessary for both induction and maintenance of pluripotency and self-renewal. Whole-genome sequencing defined a unique mutation in KLF4 (KLF4K409Q) in human meningiomas. However, the molecular mechanism of this tumor-specific KLF4 mutation is unknown. Using genome-wide high-throughput and focused quantitative transcriptional approaches in human cell lines, primary meningeal cells, and meningioma tumor tissue, we found that a change in the evolutionarily conserved DNA-binding domain of KLF4 alters its DNA recognition preference, resulting in a shift in downstream transcriptional activity. In the KLF4K409Q-specific targets, the normally silent fibroblast growth factor 3 (FGF3) is activated. We demonstrated a neomorphic function of KLF4K409Q in stimulating FGF3 transcription through binding to its promoter and in using short tandem repeats (STRs) located within the locus as enhancers.

Acetaminophen Inhibits the Neutrophil Oxidative Burst: Implications for Diagnostic Testing.

BACKGROUND: Chronic granulomatous disease is a primary immunodeficiency characterized by recurrent bacterial and fungal infections, granuloma formation, and inflammatory disease. Impaired neutrophil oxidative function is an essential diagnostic criterion. In vitro exposure of neutrophils to acetaminophen, a commonly used over-the-counter medication, has been associated with reduced neutrophil oxidative function. The clinical implications of acetaminophen intake for dihydrorhodamine (DHR) testing remain unknown. OBJECTIVE: To evaluate the effect of in vivo administration of therapeutic doses of acetaminophen on DHR diagnostic testing. METHODS: We performed DHR testing in 15 healthy adults before and after administering a single dose of acetaminophen. We retrospectively reviewed 195 DHR test results from hospitalized patients who had received acetaminophen, nonsteroidal anti-inflammatory drug, or corticosteroid before testing. RESULTS: DHR testing result was abnormal in 100% (n = 15) of healthy adults 2 hours after acetaminophen intake. We identified 195 instances of DHR testing less than or equal to 72 hours after acetaminophen ingestion in hospitalized patients who did not have chronic granulomatous disease. DHR results were abnormal in 43 of 195 cases (22.1%). Frequency of false-positive testing was increased in patients who received acetaminophen within 24 hours of testing, and in patients who received more than 1 dose of acetaminophen. Nonsteroidal anti-inflammatory drug and corticosteroid intakes were not associated with abnormal DHR result. CONCLUSIONS: Patients treated with acetaminophen have decreased neutrophil oxidative burst as measured by DHR testing. To avoid falsely abnormal testing for chronic granulomatous disease, patients should be advised to avoid acetaminophen for at least 24 hours before DHR testing.

Ligase-4 Deficiency Causes Distinctive Immune Abnormalities in Asymptomatic Individuals.

PURPOSE: DNA Ligase 4 (LIG4) is a key factor in the non-homologous end-joining (NHEJ) DNA double-strand break repair pathway needed for V(D)J recombination and the generation of the T cell receptor and immunoglobulin molecules. Defects in LIG4 result in a variable syndrome of growth retardation, pancytopenia, combined immunodeficiency, cellular radiosensitivity, and developmental delay. METHODS: We diagnosed a patient with LIG4 syndrome by radiosensitivity testing on peripheral blood cells, and established that two of her four healthy siblings carried the same compound heterozygous LIG4 mutations. An extensive analysis of the immune phenotype, cellular radiosensitivity, telomere length, and T and B cell antigen receptor repertoire was performed in all siblings. RESULTS: In the three genotypically affected individuals, variable severities of radiosensitivity, alterations of T and B cell counts with an increased percentage of memory cells, and hypogammaglobulinemia, were noticed. Analysis of T and B cell antigen receptor repertoires demonstrated increased usage of alternative microhomology-mediated end-joining (MHMEJ) repair, leading to diminished N nucleotide addition and shorter CDR3 length. However, overall repertoire diversity was preserved. CONCLUSIONS: We demonstrate that LIG4 syndrome presents with high clinical variability even within the same family, and that distinctive immunologic abnormalities may be observed also in yet asymptomatic individuals.

Human HOIP and LUBAC deficiency underlies autoinflammation, immunodeficiency, amylopectinosis, and lymphangiectasia.

Inherited, complete deficiency of human HOIL-1, a component of the linear ubiquitination chain assembly complex (LUBAC), underlies autoinflammation, infections, and amylopectinosis. We report the clinical description and molecular analysis of a novel inherited disorder of the human LUBAC complex. A patient with multiorgan autoinflammation, combined immunodeficiency, subclinical amylopectinosis, and systemic lymphangiectasia, is homozygous for a mutation in HOIP, the gene encoding the catalytic component of LUBAC. The missense allele (L72P, in the PUB domain) is at least severely hypomorphic, as it impairs HOIP expression and destabilizes the whole LUBAC complex. Linear ubiquitination and NF-κB activation are impaired in the patient's fibroblasts stimulated by IL-1ß or TNF. In contrast, the patient's monocytes respond to IL-1ß more vigorously than control monocytes. However, the activation and differentiation of the patient's B cells are impaired in response to CD40 engagement. These cellular and clinical phenotypes largely overlap those of HOIL-1-deficient patients. Clinical differences between HOIL-1- and HOIP-mutated patients may result from differences between the mutations, the loci, or other factors. Our findings show that human HOIP is essential for the assembly and function of LUBAC and for various processes governing inflammation and immunity in both hematopoietic and nonhematopoietic cells.

TB-IRIS, T-cell activation, and remodeling of the T-cell compartment in highly immunosuppressed HIV-infected patients with TB.

OBJECTIVE: To investigate the impact of tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) upon immunological recovery and the T-cell compartment after initiation of TB and antiretroviral therapy (ART). DESIGN AND METHODS: We prospectively evaluated T-cell immunophenotypes by flow cytometry and cytokines by Luminex assays in a subset (n = 154) of highly immunosuppressed HIV-infected patients with TB from the Cambodian Early versus Late Introduction of Antiretrovirals randomized clinical trial. We compared findings from patients who developed TB-IRIS with findings from patients who did not develop TB-IRIS. Data were evaluated with mixed-effect linear regression, Kaplan-Meier estimates, and Wilcoxon rank-sum tests, and q-values were calculated to control for multiple comparisons. RESULTS: Development of TB-IRIS was associated with significantly greater pre-ART frequencies of HLA-DRCD45ROCD4, CCR5CD4, OX40CD4, and Fas effector memory CD8 T cells, and significantly elevated levels of plasma interleukin (IL)-6, IL-1ß, IL-8, and IL-10, and viral load. Post-ART initiation, effector memory CD4 and Fas effector memory CD4 T-cell frequencies significantly expanded, and central memory CD4 T-cell frequencies significantly contracted in patients who experienced TB-IRIS. By week 34 post-TB treatment initiation, effector memory/central memory CD4 T-cell ratios were markedly higher in TB-IRIS versus non-TB-IRIS patients. CONCLUSIONS: A distinct pattern of pre-ART T-cell and cytokine markers appear to poise the immune response of certain patients to develop TB-IRIS. Experience of TB-IRIS is then associated with long-term remodeling of the CD4 T-cell memory compartment towards an effector memory-dominated phenotype. We speculate that these pre and post-ART TB-IRIS-associated immune parameters may contribute to superior immune control of TB/HIV co-infection and better clinical outcome.

Next generation sequencing reveals skewing of the T and B cell receptor repertoires in patients with wiskott-Aldrich syndrome.

The Wiskott-Aldrich syndrome (WAS) is due to mutations of the WAS gene encoding for the cytoskeletal WAS protein, leading to abnormal downstream signaling from the T cell and B cell antigen receptors (TCR and BCR). We hypothesized that the impaired signaling through the TCR and BCR in WAS would subsequently lead to aberrations in the immune repertoire of WAS patients. Using next generation sequencing (NGS), the T cell receptor ß and B cell immunoglobulin heavy chain (IGH) repertoires of eight patients with WAS and six controls were sequenced. Clonal expansions were identified within memory CD4(+) cells as well as in total, naïve and memory CD8(+) cells from WAS patients. In the B cell compartment, WAS patient IGH repertoires were also clonally expanded and showed skewed usage of IGHV and IGHJ genes, and increased usage of IGHG constant genes, compared with controls. To our knowledge, this is the first study that demonstrates significant abnormalities of the immune repertoire in WAS patients using NGS.

Flow cytometry biomarkers distinguish DOCK8 deficiency from severe atopic dermatitis.

DOCK8 deficiency is a primary immunodeficiency characterized by recurrent sinopulmonary infections, dermatitis with cutaneous infections, elevated serum IgE levels, eosinophilia, and a high incidence of food allergy. Given the seriousness of DOCK8 deficiency, it is important to recognize it early and initiate appropriate therapy. Diagnosis relies on examining DOCK8 protein expression and sequencing of the 48 exons in the DOCK8 gene, but these assays are not always readily available. A major problem facing clinicians is that DOCK8 deficiency shares many clinical and laboratory features with severe atopic dermatitis. Here, we have identified biomarkers routinely measured by flow cytometry on whole blood in clinical immunology laboratories that may be used in distinguishing DOCK8 deficiency from severe atopic dermatitis. The use of these biomarkers may help the clinician identify those patients who are most likely to have DOCK8 mutations and would benefit from further specialized diagnostic testing.

Hypomorphic Janus kinase 3 mutations result in a spectrum of immune defects, including partial maternal T-cell engraftment.

BACKGROUND: Mutations in Janus kinase 3 (JAK3) are a cause of severe combined immunodeficiency, but hypomorphic JAK3 defects can result in a milder clinical phenotype, with residual development and function of autologous T cells. Maternal T-cell engraftment is a common finding in infants with severe combined immunodeficiency but is not typically observed in patients with residual T-cell development. OBJECTIVE: We sought to study in detail the molecular, cellular, and humoral immune phenotype and function of 3 patients with hypomorphic JAK3 mutations. METHODS: We analyzed the distribution and function of T and B lymphocytes in 3 patients and studied the in vitro and in vivo responses of maternal T lymphocytes in 1 patient with maternal T-cell engraftment and residual production of autologous T lymphocytes. RESULTS: B cells were present in normal numbers but with abnormal distribution of marginal zone-like and memory B cells. B-cell differentiation to plasmablasts in vitro in response to CD40 ligand and IL-21 was abolished. In 2 patients the T-cell repertoire was moderately restricted. Surprisingly, 1 patient showed coexistence of maternal and autologous T lymphocytes. By using an mAb recognizing the maternal noninherited HLA-A2 antigen, we found that autologous cells progressively accumulated in vivo but did not compete with maternal cells in vitro. CONCLUSION: The study of 3 patients with hypomorphic JAK3 mutations suggests that terminal B-cell maturation/differentiation requires intact JAK3 function, even if partially functioning T lymphocytes are present. Maternal T-cell engraftment can occur in patients with JAK3 mutations despite the presence of autologous T cells.

Tumor necrosis factor receptor-associated factor 1 (TRAF1) deficiency attenuates atherosclerosis in mice by impairing monocyte recruitment to the vessel wall.

BACKGROUND: Members of the tumor necrosis factor superfamily, such as tumor necrosis factor-alpha, potently promote atherogenesis in mice and humans. Tumor necrosis factor receptor-associated factors (TRAFs) are cytoplasmic adaptor proteins for this group of cytokines. METHODS AND RESULTS: This study tested the hypothesis that TRAF1 modulates atherogenesis in vivo. TRAF1(-/-)/LDLR(-/-) mice that consumed a high-cholesterol diet for 18 weeks developed significantly smaller atherosclerotic lesions than LDLR(-/-) (LDL receptor-deficient) control animals. As the most prominent change in histological composition, plaques of TRAF1-deficient animals contained significantly fewer macrophages. Bone marrow transplantations revealed that TRAF1 deficiency in both hematopoietic and vascular resident cells contributed to the reduction in atherogenesis observed. Mechanistic studies showed that deficiency of TRAF1 in endothelial cells and monocytes reduced adhesion of inflammatory cells to the endothelium in static and dynamic assays. Impaired adhesion coincided with reduced cell spreading, actin polymerization, and CD29 expression in macrophages, as well as decreased expression of the adhesion molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in endothelial cells. Small interfering RNA studies in human cells verified these findings. Furthermore, TRAF1 messenger RNA levels were significantly elevated in the blood of patients with acute coronary syndrome. CONCLUSIONS: TRAF1 deficiency attenuates atherogenesis in mice, most likely owing to impaired monocyte recruitment to the vessel wall. These data identify TRAF1 as a potential treatment target for atherosclerosis.

ERK-dependent Bim modulation downstream of the 4-1BB-TRAF1 signaling axis is a critical mediator of CD8 T cell survival in vivo.

During an acute immune response, CD8 T cells undergo rapid expansion followed by a contraction phase during which the majority of activated T cells die, leaving a few survivors to persist as memory cells. The regulation of T cell survival is critical at each stage of this response. 4-1BB, a TNFR family member, has been implicated in prolonging the survival of activated and memory CD8 T cells; however, the precise mechanisms by which 4-1BB sustains T cell survival are incompletely understood. Upon aggregation on T cells, 4-1BB associates with two TNFR-associated factors (TRAF), TRAF1 and TRAF2. TRAF2 is essential for downstream signaling from 4-1BB; however, the role of TRAF1 in 4-1BB signaling has not been elucidated and there have been conflicting data as to whether TRAF1 provides a positive or a negative signal in T cells. In this study, we report that TRAF1 plays a critical role in survival signaling downstream of 4-1BB during CD8 T cell expansion in response to viral infection in vivo. Further analysis reveals that TRAF1-deficient cells are impaired in their ability to up-regulate the prosurvival Bcl-2 family member Bcl-x(L) and show increased levels of the proapoptotic Bcl-2 family member Bim following 4-1BB signaling. TRAF1-deficient CD8 T cells fail to activate ERK in response to 4-1BB ligation and inhibition of ERK signaling downstream of 4-1BB in wild-type cells leads to increased Bim levels. Thus, TRAF1 has a prosurvival effect in CD8 T cells via the 4-1BB-mediated up-regulation of Bcl-x(L) and ERK-dependent Bim down-modulation.

TNF receptor-associated factor 1 expressed in resident lung cells is required for the development of allergic lung inflammation.

TNF is a major therapeutic target in a range of chronic inflammatory disorders, including asthma. TNFR-associated factor (TRAF)1 is an intracellular adaptor molecule important for signaling by TNFR. In this study, we investigated the role of TRAF1 in an adoptive transfer model of allergic lung inflammation. Mice deficient in TRAF1 (TRAF1(-/-)) and wild-type (WT) control animals were adoptively transferred with WT OVA-immune CD4(+) T cells, exposed to an aerosol of LPS-free OVA, and analyzed for the development of allergic lung inflammation. In contrast to WT mice, TRAF1(-/-) recipients failed to display goblet cell hyperplasia, eosinophilic inflammation, and airway hyperresponsiveness in this model of asthma. Neither T cell recruitment nor expression of the proinflammatory cytokines IL-4, IL-5, IL-13, or TNF occurred in the lungs of TRAF1(-/-) mice. Although purified myeloid TRAF1(-/-) dendritic cells (DCs) exhibited normal Ag-presenting function and transmigratory capacity in vitro and were able to induce OVA-specific immune responses in the lung draining lymph nodes (LNs) following adoptive transfer in vivo, CD11c(+)CD11b(+) DCs from airways of TRAF1(-/-) recipients were not activated, and purified draining LN cells did not proliferate in vitro. Moreover, transfer of WT or TRAF1(-/-) DCs failed to restore T cell recruitment and DC activation in the airways of TRAF1(-/-) mice, suggesting that the expression of TRAF1 in resident lung cells is required for the development of asthma. Finally, we demonstrate that T cell-transfused TRAF1(-/-) recipient mice demonstrated impaired up-regulation of ICAM-1 expression on lung cells in response to OVA exposure.

NF-kappaB2 mutation targets TRAF1 to induce lymphomagenesis.

The NF-kappaB2 gene is recurrently mutated in human lymphoid malignancies. However, a causal relationship between NF-kappaB2 mutation and lymphomagenesis has not been established. It is also unclear how the mutation may lead to lymphoid malignancies. We report the generation of transgenic mice with targeted expression of p80HT, a lymphoma-associated NF-kappaB2 mutant, in lymphocytes. The transgenic mice display a marked expansion of peripheral B cell populations and develop predominantly small B cell lymphomas. p80HT expression has no apparent effect on the proliferation of B cells, but renders them specifically resistant to apoptosis induced by cytokine deprivation and mitogenic stimulation. Lymphocytes and lymphoma cells from p80HT mice express high levels of TRAF1, an antiapoptotic protein also implicated in lymphoid malignancies. p80HT binds the TRAF1 promoter in vivo and activates TRAF1 transcription. Moreover, TRAF1 knockdown abrogates the antiapoptotic activity of p80HT and TRAF1 deficiency reestablishes B cell homeostasis in p80HT mice. These findings demonstrate NF-kappaB2 mutation as an oncogenic event in vivo and suggest a molecular pathway for TRAF1 activation in the pathogenesis of lymphomas.

TRAF-1, -2, -3, -5, and -6 are induced in atherosclerotic plaques and differentially mediate proinflammatory functions of CD40L in endothelial cells.

OBJECTIVE: Several lines of evidence implicate CD40 ligand (CD40L, CD154) as a mediator and marker of atherosclerosis. This study investigated the involvement of tumor necrosis factor receptor-associated factors (TRAFs) in CD40 signaling in endothelial cells (ECs) and their expression in atheromata and cells involved in atherogenesis. METHODS AND RESULTS: CD40L enhanced the basal expression of TRAF-1, -2, -3, and 6, but not TRAF-5 in ECs. TRAFs associated with CD40 on ligation by CD40L. Study of ECs from TRAF-1, -2, and -5-deficient mice demonstrated functional involvement of TRAFs in proinflammatory CD40 signaling. Whereas TRAF-1 deficiency enhanced CD40L-induced IL-6 and MCP-1 expression, TRAF-2 and TRAF-5 deficiency inhibited CD40L-inducible IL-6 but not MCP-1 expression. Gene silencing in human ECs further delineated functions of TRAFs in CD40 signaling. TRAF-3 silencing in ECs showed increased CD40L-induced IL-6, MCP-1, and IL-8 expression, whereas TRAF-6 silencing increased selectively CD40L-induced MCP-1 expression. Enhanced TRAF levels in atherosclerotic lesions further supports involvement of members of this family of signaling molecules in arterial disease. CONCLUSIONS: These results implicate endothelial TRAF-1, -2, -3, -5, and -6 in CD40 signaling in atherogenesis, identifying these molecules as potential targets for selective therapeutic intervention.

TRAF1 regulates recruitment of lymphocytes and, to a lesser extent, neutrophils, myeloid dendritic cells and monocytes to the lung airways following lipopolysaccharide inhalation.

Inhaled lipopolysaccharide (LPS) induces an inflammatory response that may contribute to the pathogenesis of asthma and other airway diseases. Here we investigate the role of tumour necrosis factor (TNF) receptor-associated factor 1 (TRAF1) in leucocyte recruitment using a model of LPS-induced lung inflammation in mice. TRAF1(-/-) mice are completely deficient in the recruitment of lymphocytes to the lower respiratory tract after inhalation of LPS. Although TRAF1(-/-) mice display normal early accumulation of neutrophils, dendritic cells and monocytes in the alveolar airspace, they have a significantly reduced recruitment of these cells by 24 hr after inhalation of LPS when compared to wild-type (WT) mice. Despite normal expression of the pro-inflammatory cytokines TNF, interleukin-1 (IL-1) and IL-6 after LPS treatment, TRAF1(-/-) mice displayed decreased expression of intercellular adhesion molecule 1, vascular cell adhesion molecule 1, CCL17 and CCL20 in the lungs, when compared to LPS-treated WT mice. These results suggest that TRAF1 facilitates LPS-induced leucocyte recruitment into the lung airways by augmenting the expression of chemokines and adhesion molecules. Mice lacking TNF receptor 1 (TNFR1) but not TNFR2 show a phenotype similar to the TRAF1(-/-) mice, suggesting that TRAF1 may act downstream of TNFR1. Significantly, we use bone marrow chimeras to demonstrate that expression of TRAF1 by cells resident in the lungs, but not by circulating leucocytes, is necessary for efficient LPS-induced recruitment of leucocytes to the lung airways.