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Hypersensitivity pneumonitis (HP) is an inflammatory lung disease caused by the repeated inhalation of aerosolized antigens. With chronic exposure to an inhaled antigen, patients are at risk of developing irreversible pulmonary fibrosis as well as an increased morbidity and mortality. Although alphabeta T cells have been shown to be important in the pathogenesis of HP, gammadelta T cells also accumulate in the bronchoalveolar lavage of patients with HP. gammadelta T cells represent a distinct lymphocyte subset, whose primary function is not well understood. In contrast to alphabeta T cells, gammadelta T cells recognize unprocessed antigens, such as those upregulated on injured or stressed epithelial cells. In a murine model of HP induced by exposure to the ubiquitous microorganism Bacillus subtilis, gammadelta T cells expressing the canonical Vgamma6/Vdelta1 T cell receptor were dramatically expanded in the lung. The predominant cytokines expressed by this gammadelta T-cell subset were T-helper 17 (Th17) cytokines that were critical for bacterial clearance and the resolution of lung inflammation. Th17-expressing gammadelta T cells are also expanded in other murine models of lung infection and inflammation, which suggests that these cells play a sentinel role in mucosal immunity. Thus, an increased understanding of gammadelta T cells that express Th17 cytokines in HP and other inflammatory lung diseases may lead to the development of novel therapeutic and clinical strategies that prevent the development of fibrotic lung disease. [ABSTRACT FROM AUTHOR]

Rationale: Within the lungs of patients with severe emphysema, inflammation continues despite smoking cessation. Foci of T lymphocytes in the small airways of patients with emphysema have been associated with disease severity. Whether these T cells play an important role in this continued inflammatory response is unknown.Objective: The aim of this study was to determine if T cells recruited to the lungs of subjects with severe emphysema contain oligoclonal T-cell populations, suggesting their accumulation in response to antigenic stimuli.Methods: Lung T-cell receptor (TCR) Vbeta repertoire from eight patients with severe emphysema and six control subjects was evaluated at the time of tissue procurement (ex vivo) and after 2 weeks of culture with interleukin 2 (in vitro). Junctional region nucleotide sequencing of expanded TCR-Vbeta subsets was performed.Results: No significantly expanded TCR-Vbeta subsets were identified in ex vivo samples. However, T cells grew from all emphysema (n = 8) but from only one of the control lung samples (n = 6) when exposed to interleukin 2 (p = 0.0013). Within the cultured cells, seven major CD4-expressing TCR-Vbeta subset expansions were identified from five of the patients with emphysema. These expansions were composed of oligoclonal populations of T cells that had already been expanded in vivo.Conclusion: Severe emphysema is associated with inflammation involving T lymphocytes that are composed of oligoclonal CD4+ T cells. These T cells are accumulating in the lung secondary to conventional antigenic stimulation and are likely involved in the persistent pulmonary inflammation characteristic of severe emphysema. [ABSTRACT FROM AUTHOR]

Alcohol use disorders (AUDs) and tobacco smoking are associated with an increased predisposition for community-acquired pneumonia and the acute respiratory distress syndrome. Mechanisms are incompletely established but may include alterations in response to pathogens by immune cells, including alveolar macrophages (AMs) and peripheral blood mononuclear cells (PBMCs). We sought to determine the relationship of AUDs and smoking to expression of IFNγ, IL-1β, IL-6, and TNFα by AMs and PBMCs from human subjects after stimulation with lipopolysaccharide (LPS) or lipoteichoic acid (LTA). AMs and PBMCs from healthy subjects with AUDs and controls, matched on smoking, were cultured with LPS (1 μg/ml) or LTA (5 μg/ml) in the presence and absence of the antioxidant precursor N-acetylcysteine (10 mM). Cytokines were measured in cell culture supernatants. Expression of IFNγ, IL-1β, IL-6, and TNFα in AMs and PBMCs was significantly increased in response to stimulation with LPS and LTA. AUDs were associated with augmented production of proinflammatory cytokines, particularly IFNγ and IL-1β, by AMs and PBMCs in response to LPS. Smoking diminished the impact of AUDs on AM cytokine expression. Expression of basal AM and PBMC Toll-like receptors-2 and -4 was not clearly related to differences in cytokine expression; however, addition of N-acetylcysteine with LPS or LTA led to diminished AM and PBMC cytokine secretion, especially among current smokers. Our findings suggest that AM and PBMC immune cell responses to LPS and LTA are influenced by AUDs and smoking through mechanisms that may include alterations in cellular oxidative stress., (Copyright © 2016 the American Physiological Society.)

γδ T lymphocytes are a unique T cell population with important anti-inflammatory capabilities. Their role in acute lung injury, however, is poorly understood but may provide significant insight into lung-protective mechanisms occurring after injury. In a murine model of lung injury, wild-type C57BL/6 and TCRδ(-/-) mice were exposed to Escherichia coli LPS, followed by analysis of γδ T cell and macrophage subsets. In the absence of γδ T cells, TCRδ(-/-) mice developed increased inflammation and alveolar-capillary leak compared with wild-type C57BL/6 mice after LPS exposure that correlated with expansion of distinct macrophage populations. Classically activated M1 macrophages were increased in the lung of TCRδ(-/-) mice at d 1, 4, and 7 after LPS exposure that peaked at d 4 and persisted at d 7 compared with wild-type animals. In response to LPS, Vγ1 and Vγ7 γδ T cells were expanded in the lung and expressed IL-4. Coculture experiments showed decreased expression of TNF-α by resident alveolar macrophages in the presence of γδ T cells that was reversed in the presence of an anti-IL-4-blocking antibody. Treatment of mice with rIL4 resulted in reduced numbers of M1 macrophages, inflammation, and alveolar-capillary leak. Therefore, one mechanism by which Vγ1 and Vγ7 γδ T cells protect against LPS-induced lung injury is through IL-4 expression, which decreases TNF-α production by resident alveolar macrophages, thus reducing accumulation of M1 macrophages, inflammation, and alveolar-capillary leak., (© Society for Leukocyte Biology.)

Susceptibility to chronic beryllium disease (CBD) is linked to certain HLA-DP molecules, including HLA-DP2. To elucidate the molecular basis of this association, we exposed mice transgenic (Tg) for HLA-DP2 to beryllium oxide (BeO) via oropharyngeal aspiration. As opposed to WT mice, BeO-exposed HLA-DP2 Tg mice developed mononuclear infiltrates in a peribronchovascular distribution that were composed of CD4(+) T cells and included regulatory T (Treg) cells. Beryllium-responsive, HLA-DP2-restricted CD4(+) T cells expressing IFN-γ and IL-2 were present in BeO-exposed HLA-DP2 Tg mice and not in WT mice. Using Be-loaded HLA-DP2-peptide tetramers, we identified Be-specific CD4(+) T cells in the mouse lung that recognize identical ligands as CD4(+) T cells derived from the human lung. Importantly, a subset of HLA-DP2 tetramer-binding CD4(+) T cells expressed forkhead box P3, consistent with the expansion of antigen-specific Treg cells. Depletion of Treg cells in BeO-exposed HLA-DP2 Tg mice exacerbated lung inflammation and enhanced granuloma formation. These findings document, for the first time to our knowledge, the development of a Be-specific adaptive immune response in mice expressing HLA-DP2 and the ability of Treg cells to modulate the beryllium-induced granulomatous immune response.

The innate immune system causes tissue inflammation and injury after renal ischemia/reperfusion (I/R). The complement system is activated on ischemic tubular epithelial cells (TECs) and induces the cells to produce pro-inflammatory chemokines. TECs also express toll-like receptors (TLRs)-2 and -4. Signaling through the TLRs induces TECs to produce a variety of chemokines, some of which can also be induced by complement activation fragments. We sought to determine whether the effects of complement activation and TLR signaling in TECs are redundant, or whether additive protection can be achieved by blocking both of these innate immune systems. To confirm that the complement system, TLR-2 signaling, and TLR-4 signaling induce production of a similar repertoire of inflammatory chemokines, we stimulated TECs with complement sufficient serum or with TLR-2 and TLR-4 ligands in vitro. We found that all three of these stimuli induce TECs to produce KC, MIP-2, IL-6, and TNF-α, and that there was a trend toward greater production of KC in cells exposed to two stimuli. Based upon these results, we hypothesized that mice deficient in both complement activation and TLR-2 signaling would demonstrate greater protection from I/R than mice deficient only in the complement system. To test this hypothesis we induced ischemic acute kidney injury (AKI) in wild-type mice, mice with targeted deletion of complement factor B (fB(-/-) mice), or mice with targeted deletion of factor B and TLR-2 (fB(-/-)TLR2(-/-) mice). Surprisingly, we found that fB(-/-)TLR2(-/-) mice developed more severe injury than those with single deficiency of factor B. Our results indicate that blockade of the complement system may be more protective than simultaneous blockade of both the complement system and TLR-2 in ischemic AKI., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Objective: To evaluate the presence of pulmonary abnormalities in rheumatoid arthritis (RA)-related autoantibody-positive subjects without inflammatory arthritis., Methods: Forty-two subjects who did not have inflammatory arthritis but were positive for anti-cyclic citrullinated peptide antibodies and/or ≥2 rheumatoid factor isotypes (a profile that is 96% specific for RA), 15 autoantibody-negative controls, and 12 patients with established seropositive early RA (<1-year duration) underwent spirometry and high-resolution computed tomography (HRCT) lung imaging., Results: The median age of autoantibody-positive subjects was 54 years, 52% were female, and 38% were ever-smokers; these characteristics were not significantly different from those of autoantibody-negative control subjects. No autoantibody-positive subject had inflammatory arthritis based on joint examination. HRCT revealed that 76% of autoantibody-positive subjects had airways abnormalities including bronchial wall thickening, bronchiectasis, centrilobular opacities, and air trapping, compared with 33% of autoantibody-negative controls (P = 0.005). The prevalence and type of lung abnormalities among autoantibody-positive subjects were similar to those among patients with early RA. In 2 autoantibody-positive subjects with airways disease, inflammatory arthritis classifiable as articular RA developed ∼13 months after the lung evaluation., Conclusion: Airways abnormalities that are consistent with inflammation are common in autoantibody-positive subjects without inflammatory arthritis and are similar to airways abnormalities seen in patients with early RA. These findings suggest that the lung may be an early site of autoimmune-related injury and potentially a site of generation of RA-related autoimmunity. Further studies are needed to define the mechanistic role of lung inflammation in the development of RA., (Copyright © 2012 by the American College of Rheumatology.)

Inflammation-induced pulmonary fibrosis (PF) leads to irreversible loss of lung function and is a predictor of mortality in numerous lung diseases. Why some subjects with lung inflammation but not others develop PF is unclear. In a mouse model of hypersensitivity pneumonitis that progresses to lung fibrosis upon repeated exposure to the ubiquitous microorganism Bacillus subtilis, γδ T cells expand in the lung and inhibit collagen deposition. We show that a subset of these γδ cells represents the predominant source of the Th17 cytokine IL-22 in this model. Preventing expression of IL-22, either by mutating the aryl hydrocarbon receptor (AhR) or inhibiting AhR signaling, accelerated lung fibrosis. Direct blockade of IL-22 also enhanced collagen deposition in the lung, whereas administration of recombinant IL-22 inhibited lung fibrosis. Moreover, the presence of protective γδ T cells and IL-22 diminished recruitment of CD4(+) T cells to lung. These data reveal a protective pathway that involves the inhibition of αβ T cells by regulatory IL-22-secreting γδ T cells.

Hypersensitivity pneumonitis (HP) is an inflammatory lung disease characterized by a diffuse mononuclear cell infiltrate in the lung that can progress to pulmonary fibrosis with chronic exposure to an inhaled Ag. We previously reported that C57BL/6 mice repeatedly exposed to the ubiquitous microorganism Bacillus subtilis develop mononuclear infiltrates in the lung that contain Vgamma6/Vdelta1(+) gammadelta T cells. In the absence of this T cell subset, mice treated with B. subtilis had significantly increased collagen deposition in the lung, suggesting a regulatory role for Vgamma6/Vdelta1(+) gammadelta T cells. To further investigate the role of Vgamma6/Vdelta1(+) gammadelta T cells in B. subtilis-induced lung fibrosis, we exposed transgenic Vgamma6/Vdelta1 mice to this microorganism and found decreased collagen content in the lung compared with wild-type C57BL/6 mice. Cytokine analysis of lung homogenates from wild-type C57BL/6 mice demonstrated increased IL-17A concentrations with repeated exposure to B. subtilis. In the absence of IL-17 receptor signaling, IL-17ra(-/-) mice had delayed clearance of B. subtilis with increased lung inflammation and fibrosis. Although IL-17A was predominantly expressed by Vgamma6/Vdelta1(+) T cells, a compensatory increase in IL-17A expression by CD4(+) T cells was seen in the absence of gammadelta T cells that resulted in similar levels of IL-17A in the lungs of TCRdelta(-/-) and wild-type C57BL/6 mice. In combination, our data suggest an important role for IL-17A-expressing T lymphocytes, both gammadelta and alphabeta T cells, in eliminating this microorganism that prevents excessive inflammation and eventual lung fibrosis in this murine model of B. subtilis-induced hypersensitivity pneumonitis.

The resident population of γδ T cells in the normal lung is small but during lung inflammation, γδ T cells can increase dramatically. Histological analysis reveals diverse interactions between γδ T cells and other pulmonary leukocytes. Studies in animal models show that γδ T cells play a role in allergic lung inflammation where they can protect normal lung function, that they also are capable of resolving infection-induced pulmonary inflammation, and that they can help preventing pulmonary fibrosis. Lung inflammation threatens vital lung functions. Protection of the lung tissues and their functions during inflammation is the net-effect of opposing influences of specialized subsets of γδ T cells as well as interactions of these cells with other pulmonary leukocytes.

Hypersensitivity pneumonitis is an environmental lung disease characterized by a diffuse mononuclear cell infiltrate in the lung that can progress to pulmonary fibrosis with chronic exposure to an inhaled Ag. Using a well-established murine model of hypersensitivity pneumonitis, we repeatedly exposed C57BL/6 mice to Saccharopolyspora rectivirgula to investigate whether T cells are required for lung fibrosis. In the absence of alphabeta T cells, TCRbeta(-/-) mice exposed to S. rectivirgula for 4 wk had markedly decreased mononuclear infiltrates and collagen deposition in the lung compared with wild-type C57BL/6 mice. In contrast to CD8(+) T cells, adoptive transfer of CD4(+) T cells reconstituted the S. rectivirgula-induced inflammatory and fibrotic response, suggesting that the CD4(+) T cell represents the critical alphabeta T cell subset. Cytokine analysis of lung homogenates at various time points after S. rectivirgula exposure failed to identify a predominant Th1 or Th2 phenotype. Conversely, IL-17 was found in the lung at increasing concentrations with continued exposure to S. rectivirgula. Intracellular cytokine staining revealed that 14% of CD4(+) T cells from the lung of mice treated with S. rectivirgula expressed IL-17A. In the absence of IL-17 receptor signaling, Il17ra(-/-) mice had significantly decreased lung inflammation and fibrosis compared with wild-type C57BL/6 mice. These data are the first to demonstrate an important role for Th17-polarized CD4(+) T lymphocytes in the immune response directed against S. rectivirgula in this murine model of hypersensitivity pneumonitis and pulmonary fibrosis.

IL-17 is a cytokine that plays an important role in orchestrating innate immune function. In addition, IL-17 has been shown to exacerbate autoimmune diseases. CD4(+) alphabeta T cells, gammadelta T cells, and NK cells all produce IL-17. Th17 cells are a newly defined alphabeta(+) T cell lineage characterized by IL-17 production. However, gammadelta T cells are often the major source of this cytokine. Their response can be very rapid during bacterial infections and has been shown to be protective, but IL-17-producing gammadelta T cells have also been found to exacerbate collagen-induced arthritis. Interestingly, some gammadelta T cells produce IL-17 in response to IL-23 alone, even in naïve animals, suggesting they are already differentiated and may develop differently than CD4(+) alphabeta Th17 cells.

The mechanisms by which T cells accumulate in the lungs of patients with pulmonary fibrosis are poorly understood. Because the lung is continually exposed to microbial agents from the environment, we repeatedly exposed C57BL/6 mice to the ubiquitous microorganism, Bacillus subtilis, to determine whether chronic exposure to an inhaled microorganism could lead to T cell accumulation in the lungs and subsequent pulmonary fibrosis. C57BL/6 mice repeatedly treated with B. subtilis for 4 consecutive weeks developed a 33-fold increase in the number of CD4+ T cells and a 354-fold increase in gammadelta T cells in the lung. The gammadelta T cells consisted almost entirely of Vgamma6/Vdelta1+ cells, a murine subset bearing an invariant TCR the function of which is still unknown. Treatment of C57BL/6 mice with heat-killed vs live B. subtilis resulted in a 2-fold increase in the number of CD4+ T cells in the lung but no expansion of gammadelta T cells indicating that gammadelta cells accumulate in response to live microorganisms. In addition, mice treated with heat-killed B. subtilis developed significantly increased pulmonary fibrosis compared with mice treated with the live microorganism. Mice deficient in Vgamma6/Vdelta1+ T cells when treated with B. subtilis had a 231-fold increase in lung CD4+ T cells and significantly increased collagen deposition compared with wild-type C57BL/6 mice, consistent with an immunoregulatory role for the Vgamma6/Vdelta1 T cell subset. These findings indicate that chronic inhalation of B. subtilis can result in T cell accumulation in the lung and fibrosis, constituting a new model of immune-mediated pulmonary fibrosis.

Bak has been shown to both promote apoptosis and to inhibit cell death while two other members of the Bcl-2 family of proteins, Bcl-XL and Bcl-2 delay apoptosis induced by various stimuli including chemotherapeutic agents. We generated clones with stable expression of Bak wild-type (wt) and Bak with its BH3 (delta78-86) domain deleted (deltaBH3) in FL5.12 cells or FL5.12 cells expressing either Bcl-XL or Bcl-2 to determine if Bak could accelerate apoptosis and antagonize the death repressor activity of Bcl-XL and Bcl-2 during chemotherapy-induced apoptosis. We found that Bak accelerated cell death in FL5.12 cells treated with etoposide, fluorouracil or taxol. In FL5.12 cells expressing Bcl-XL and Bak wt or Bak deltaBH3, both Bak wt or Bak deltaBH3 were able to antagonize the protective effect of Bcl-XL when treated with etoposide or fluorouracil. Bak wt or Bak deltaBH3 were also able to abrogate the protective effect of Bcl-2 in cells expressing Bcl-2 and Bak wt or Bak deltaBH3 when challenged by etoposide or fluorouracil. Immunoprecipitation studies revealed that deletion of BH3 disrupted heterodimerization between Bak and Bcl-XL and that both Bak wt and Bak deltaBH3 failed to interact with Bcl-2. These results demonstrate that Bak does not require its BH3 domain to promote apoptosis in stably transfected cells. Furthermore, Bak can accelerate chemotherapy-induced cell death independently of its heterodimerization with Bcl-XL and Bcl-2.

Bcl-2 and its homologue Bcl-XL are expressed in a variety of tumors and their expression modulates the sensitivity of tumor cells to a wide spectrum of chemotherapeutic agents and gamma-irradiation. In the present report, we generated clones of FL5.12 lymphoid cells with similar levels of Bcl-2 and Bcl-XL using the Flag epitope to determine if these survival proteins could provide equivalent protection when challenged with chemotherapy or gamma-irradiation. Using four M-phase specific chemotherapeutic agents, Bcl-XL and Bcl-2 provided similar protection against vincristine and vinblastine whereas Bcl-XL afforded as much as 50% greater cell viability than Bcl-2 against etoposide and teniposide-induced cell death. In addition, Bcl-XL provided significantly greater cell viability than Bcl-2 against methotrexate, fluorouracil, and hydroxyurea, three S-phase specific agents. In apoptosis induced by gamma-irradiation and cisplatin, two antitumor treatments that are cell-cycle phase-nonspecific agents, both Bcl-XL and Bcl-2 conferred similar protection against gamma-irradiation, but Bcl-XL provided better protection than Bcl-2 against cisplatin. These results indicate that Bcl-XL and Bcl-2 confer a differential ability to protect against chemotherapy-induced cell death, which appears to be dependent on the molecular mechanism targeted by the drug rather than its cell-cycle phase specificity.

Bax, a member of the Bcl-2 family of proteins, has been shown to accelerate apoptosis induced by growth factor withdrawal, gamma-irradiation, and the chemotherapeutic agent, etoposide. The mechanism by which Bax promotes apoptosis is poorly understood. Bax forms homodimers which have been suggested to act as accelerators or inducers of cell death. However, the requirement for homodimerization of Bax to promote cell death remains unclear. We performed site-directed mutagenesis of the BH1, BH2, and BH3 in Bax to determine the regions of Bax required for homodimerization and to define the role of Bax homodimers in cell death induced by chemotherapy drugs. Bax proteins expressing alanine substitutions of the highly conserved amino acids glycine 108 (G108) in BH1, tryptophan 158 (W158) in BH2, and glycine 67 and aspartic acid 68 (GD67-68) in BH3 as well as deletion of the most conserved amino acids in BH1 (Delta102-112) and BH2 (Delta151-159) and deletion of BH3 (Delta63-71) maintained their ability to accelerate chemotherapy-induced cell death. Immunoprecipitation studies revealed that Bax with deletions in BH1 and BH2 still associated with wild-type Bax while deletion of BH3 disrupted Bax homodimerization. These results demonstrate that Bax does not require the conserved regions of homology, BH1, BH2, or BH3, to accelerate chemotherapy-induced cell death. Furthermore, our results established BH3 as a region required for Bax homodimerization in mammalian cells and demonstrate that monomeric forms of Bax are active in accelerating cell death induced by chemotherapy agents.

Bax, a member of the Bcl-2 family of proteins, has been shown to promote apoptosis while other members of the family, including Bcl-XL and Bcl-2, inhibit cell death induced by a variety of stimuli. The mechanism by which Bax promotes cell death is poorly understood. In the present report, we assessed the ability of Bax to antagonize the death repressor activity of Bcl-XL during chemotherapy-induced apoptosis in the lymphoid cell line, FL5.12. Expression of wild-type Bax countered the repressor activity of Bcl-XL against cell death mediated by VP-16 and cisplatin. We performed site-directed mutagenesis of the BH1, BH2, and BH3 homology regions in Bax to determine the ability of wild-type and mutant Bax to heterodimerize with Bcl-XL and to antagonize the protective effect of Bcl-XL against chemotherapy-induced apoptosis. Bax proteins expressing alanine substitutions of the highly conserved amino acids glycine 108 in BH1, tryptophan 151 and 158 in BH2, and glycine 67 and aspartic acid 68 in BH3 retained their ability to promote chemotherapy-induced cell death that was inhibited by Bcl-XL and to form heterodimers with Bcl-XL. Bax proteins containing deletions of the most highly conserved amino acids in BH1 (Delta102-112) and BH2 (Delta151-159) maintained the ability of Bax to antagonize the death repressor activity of Bcl-XL and to associate with Bcl-XL. However, Bax with BH3 deleted did not form heterodimers with Bcl-XL, but retained its ability to counter the death repressor activity of Bcl-XL. These results demonstrate that the conserved BH3, but not BH1 or BH2, homology region of Bax is necessary for its interaction with Bcl-XL in mammalian cells. Furthermore, our results indicate that Bax does not require BH1, BH2, BH3, or heterodimerization with Bcl-XL to counter the death repressor activity of Bcl-XL. Therefore, Bax can antagonize Bcl-XL during VP-16 and, in a lesser degree, during cisplatin-induced cell death independent of its heterodimerization with Bcl-XL.

Several recently identified proteins such as Bcl-2 and Bcl-x have been found to regulate programmed cell death (i.e., apoptosis). In this report, we examined the levels of expression of proteins that can either prevent apoptosis (i.e., Bcl-2 or the long form of Bcl-x, designated Bcl-x1) or promote apoptosis (i.e., Bax or the short form of Bcl-x, designated Bcl-xs) in proliferating benign and malignant endothelial cells (ECs). In normal skin with quiescent ECs, no detection by immunohistochemical staining was observed for Bcl-xL, Bcl-xs, or Bcl-2. However, in diseased skin samples that feature a prominent angiogenic response such as in psoriasis or pyogenic granulomas, the proliferating ECs markedly overexpressed Bcl-xL, with little to no Bcl-2. In an acquired-immune-deficiency-syndrome-related neoplasm, Kaposi's sarcoma, the spindle-shaped tumor cells also overexpressed Bcl-xL compared with Bcl-2. These in vivo studies were extended in vitro using cultured ECs and Kaposi's sarcoma tumor cells that were examined by flow cytometry and immunoblot analysis. Both cultured ECs and Kaposi's sarcoma tumor cells express significantly higher levels of Bcl-xL than Bcl-2. Such overexpression of cell survival gene products may contribute to prolonging the longevity of EC-derived cells in several different benign and neoplastic skin disorders that are characterized by a prominent angiogenic tissue response.

The demise of B cell progenitors expressing functional IgM receptors for self appears to be the main mechanism by which B cell tolerance is accomplished. The genetic mechanisms that regulate the death process during this critical step of B cell development are still poorly understood. We have studied the regulation of apoptosis in WEHI-231 lymphoma cells after treatment with a panel of anti-IgM mAbs as an in vitro model of clonal B cell deletion. We showed that a product of bcl-x, Bcl-xL, can inhibit anti-IgM-induced apoptosis but not cell cycle arrest in a dose-dependent manner. Bcl-xL was efficient in protecting B cells from low but not high avidity anti-IgM mAbs. In contrast to that observed with Bcl-xL, CD40 stimulation was efficient in inhibiting both cell cycle arrest and apoptosis after IgM cross-linking regardless of the binding avidity of the anti-IgM Ab. Moreover, activation through IgM receptors but not CD40 induced up-regulation followed by rapid down-modulation of Bcl-xL. Thus, the capacity of Bcl-xL to modulate anti-IgM-induced apoptosis in WEHI-231 cells is highly dependent on the avidity of the Ab-IgM receptor interaction.