Increased acute-phase response and renal amyloidosis in aged CD2-fas-transgenic mice

We previously demonstrated that increased Fas expression in T cells of aged CD2-fas transgenic (Fas-Tg) CD-1 mice results in an increased immune response and T cell apoptosis. Surprisingly, despite prevention of T cell immune senescence, the average life span of Fas-Tg mice is comparable with that of nontransgenic (non-Tg) mice. Histopathologic evaluation of tissue sections showed that nearly 50% of the aged (>18-mo-old) Fas-Tg mice developed renal amyloid A amyloidosis, whereas no amyloid deposition was observed in aged non-Tg mice. The amyloid A deposition was observed primarily in glomeruli by using immunohistochemical stains and electron microscopy. The full-length amino acid coding sequence of serum amyloid A2 cDNA in CD-1 mice was identical to that of amyloid A amyloidosis-susceptible BALB/c mice. Although there was no significant difference in steady-state serum amyloid A level in the serum of aged non-Tg and Fas-Tg mice, challenging mice with staphylococcal enterotoxin B resulted in significantly higher serum levels of serum amyloid A on day 2 and IL-6 on days 1 and 2 and a higher magnitude of weight loss on day 7 in aged Fas-Tg mice compared with young mice. These parameters, at the indicated time points, were equivalent between young and aged non-Tg mice. Taken together, our data suggest that prevention of T cell senescence in Fas-Tg mice may be a factor in induction of an excessive acute-phase response triggered by T cell activation. The Fas-Tg mice are a novel model for understanding the immunologic mechanisms leading to secondary amyloidosis.

Increased acute-phase response and renal amyloidosis in aged CD2-fas-transgenic mice

We previously demonstrated that increased Fas expression in T cells of aged CD2-fas transgenic (Fas-Tg) CD-1 mice results in an increased immune response and T cell apoptosis. Surprisingly, despite prevention of T cell immune senescence, the average life span of Fas-Tg mice is comparable with that of nontransgenic (non-Tg) mice. Histopathologic evaluation of tissue sections showed that nearly 50% of the aged (>18-mo-old) Fas-Tg mice developed renal amyloid A amyloidosis, whereas no amyloid deposition was observed in aged non-Tg mice. The amyloid A deposition was observed primarily in glomeruli by using immunohistochemical stains and electron microscopy. The full-length amino acid coding sequence of serum amyloid A2 cDNA in CD-1 mice was identical to that of amyloid A amyloidosis-susceptible BALB/c mice. Although there was no significant difference in steady-state serum amyloid A level in the serum of aged non-Tg and Fas-Tg mice, challenging mice with staphylococcal enterotoxin B resulted in significantly higher serum levels of serum amyloid A on day 2 and IL-6 on days 1 and 2 and a higher magnitude of weight loss on day 7 in aged Fas-Tg mice compared with young mice. These parameters, at the indicated time points, were equivalent between young and aged non-Tg mice. Taken together, our data suggest that prevention of T cell senescence in Fas-Tg mice may be a factor in induction of an excessive acute-phase response triggered by T cell activation. The Fas-Tg mice are a novel model for understanding the immunologic mechanisms leading to secondary amyloidosis.

[Cloning of BRCA1 cDNA and detection of BRCA1 mRNA expression in breast cancer cells]

The fragment of BRCA1 cDNA obtained by reverse transcription and polymerase chain reaction(RT-PCR) was inserted into plasmid pUC118 and demonstrated by DNA sequencing. Nucleotide sequence analysis demonstrated that the cloned cDNA for BRCA1 includes zinc finger domain. Two differences in nucleotides were found as compared with the sequence published. One occurs at nucleotide number 409 where Creplaced by A (Asp-->Glu). Another difference occurs at nucleotide number 879 where A replaced by T (samesense mutation). In order to further study the relationship-between BRCA1 function and breast cancer, the probe was prepared from the recombinant plasmid and then hybridized to total RNAs from 6 cases of breast cancer. Compared with normal cells, the expression level of BRCA1 mRNA was normal in 4, decreased markedly in 1, and in one patient there was no any expression of BRCA1 mRNA at all. The results suggested that the expression of BRCA1 mRNA was relatively low in some breast cancer cells.

[Study on the inclusion compound of phyllostachysin A and DMF]

The crystal structure of inclusion compound phyllostachysin A[1] and DMF, C20H26O6.C3H7ON, was determined by X-ray diffraction. A colorless block crystal with dimensions of 0.6 x 0.6 x 0.8 mm was used for analysis. It shows orthorhombic, and it's space group is P2(1)2(1)2(1) with a = 10.895(3), b = 13.237(2), c = 15.373(3) A, V = 2217.0(3) A3 Z = 4, Dc = 1.302 g cm-3. Direct method was applyed to determine the structure, and the parameters were refined by least square method. The final Rf factor is 0.060 and Rw = 0.083. The result shows that the crystal is formed by Phyllostachysin A and DMF by inclusion interaction.

Hypovirulence and Double-Stranded RNA in Sclerotinia homoeocarpa

ABSTRACT One hundred and thirty-two isolates of Sclerotinia homoeocarpa, the causal agent of dollar spot of turfgrass, were evaluated for virulence on swards and detached leaves of creeping bentgrass and for the presence of double-stranded RNA (dsRNA). In at least four isolates, the hypovirulent phenotype was associated with the presence of specific segments of dsRNA. In addition, these hypovirulent isolates often grew slowly on potato dextrose agar (PDA), formed thin colonies with atypical colony margins, and failed to produce typical black stroma. The hypovirulent phenotype and dsRNA were transmitted from hypovirulent isolate Sh12B to virulent isolate Sh48B, and the converted isolate was hypovirulent and contained dsRNA. The hypovirulent phenotype and dsRNA also were transmitted to at least four other isolates of the pathogen, including the fungicide-resistant, dsRNA isolate KY-7. Converted isolates of KY-7 developed the hypovirulent phenotype, grew on fungicide-amended medium, and contained dsRNA. Subcultures of hypovirulent isolate Sh12B that did not contain dsRNA were obtained through curative treatment using cycloheximide-containing medium and heat. Cured subcultures grew faster on PDA, had more typical colony morphologies, were more virulent on bentgrass leaves, and did not contain dsRNA. No cured subcultures were obtained from hypovirulent isolate Sh09B. Isolates regenerated from protoplasts of hypovirulent isolate Sh12B were not cured, remained hypovirulent, and contained dsRNA. Transmission of hypovirulence and dsRNA in S. homoeocarpa has potential as a novel approach to the management of dollar spot of turfgrass.

Kinetics of Fas-induced apoptosis in thymic organ culture

Although most thymocytes express high levels of Fas antigen (CD95), the role of Fas in apoptosis signaling during thymocyte maturation has not been defined. Fas apoptosis occurs primarily in the CD4+CD8+ subpopulations of thymocytes. Fas expression and apoptosis function were investigated in the CD4-8-, CD4+8+, and CD4+ and CD8 single positive thymocyte subpopulations by in vivo injection of anti-Fas and in vitro incubation of Fas with thymic organ cultures. Fas was first expressed on CD4-8- thymocytes coincident with expression of IL-2R and CD44. In Fas mutant lpr/lpr mice, defective Fas expression correlated with overproduction of late-stage CD4-8(-)-thymocytes. Fas was highly expressed on CD3dull and CD3bright thymocytes. CD4+8+CD3dull thymocytes were sensitive to Fas apoptosis, whereas more mature CD4+8+CD3bright thymocytes were resistant to Fas apoptosis. Anti-Fas incubation with established thymic organ culture for 24 hr resulted in apoptosis of approximately 25% of thymocytes. Continued incubation of thymic organ culture with anti-Fas resulted in an apoptosis rate of 25% of CD4+CD8+ thymocytes per day for the first 3 days of culture. Continued culture for further time points up to 6 days did not result in further apoptosis of the CD4+CD8+ thymocytes. These results suggest that CD4-CD8-CD44+ IL-2R+ thymocytes express Fas and there is overpopulation of the subsequent developmental stage of thymocytes in Fas mutant lpr mice. Also, early-stage CD4+8+ thymocytes are susceptible to Fas apoptosis, whereas Fas apoptosis resistance is required after 3 days of thymic organ culture. We conclude that these two populations of thymocytes are susceptible to Fas ligand-mediated apoptosis during T cell development in the thymus.

Role of hydrazine in the mechanism of isoniazid hepatotoxicity in rabbits

Isoniazid (INH) continues to be a highly effective drug in the chemoprophylaxis and treatment of tuberculosis; however, its use is associated with hepatotoxicity (predominantly hepatic necrosis) in 1-2% of individuals. The INH metabolites, acetylhydrazine and hydrazine, have each been implicated as the causative hepatotoxin in INH-induced hepatotoxicity. Using a model of INH-induced hepatotoxicity in rabbits, in which INH-induced hepatotoxicity manifests as hepatic necrosis, hepatic steatosis (hepatic fat accumulation) and hypertriglyceridaemia (elevated plasma triglycerides), we compared the severity of these measures of toxicity with plasma levels of INH, acetylhydrazine and hydrazine. Plasma INH and acetylhydrazine were not correlated with markers of INH-induced hepatic necrosis or fatty changes. Plasma hydrazine at 32 h was correlated significantly with plasma argininosuccinic acid lyase (ASAL, a sensitive marker of hepatic necrosis) activity as area under the curve (r2 = 0.54, P < 0.002) and log plasma ASAL activity at 48 h after the first dose of INH (r2 = 0.53, p < 0.005), but not with fatty changes. These results show in this model of INH-induced hepatotoxicity in rabbits that hydrazine, and not INH or acetylhydrazine, is most likely involved in the pathogenic mechanism of hepatic necrosis.

Autoimmune disease results from multiple interactive defects in apoptosis induction molecules and signaling pathways

Activation induced cell death (AICD) plays a critical role in eliminating autoimmune cells and limiting inflammation after activation. The two major signaling molecules for AICD are the Fas and TNF-R pathways of apoptosis. Defective Fas apoptosis in lpr/lpr mice results in a compensatory increase in TNF-R/TNF-mediated apoptosis. TNF/TNF-R has been shown to be a compensatory pathway of apoptosis in T cells and macrophages of lpr/lpr mice. Therefore, early production of TNF/TNF-R limit an immune response by inducing AICD in the absence of an intact Fas/Fas ligand apoptosis pathway. However, increased TNF production in lpr mice also lead to increased susceptibility to septic shock and autoimmune disease such as arthritis. Therefore TNF production during an inflammatory response can downmodulate this response, but this also results in the failure to downmodulate TNF production leading to septic shock and arthritis. A second pathway of AICD is mediated by Nur77 after T cell stimulation through the CD3 molecule. Mice with defective Nur77 signaling undergo AICD using the Fas-Fas ligand pathway to eliminate autoreactive T cells. A third defect of AICD is observed in HCP-mutant me/me (motheaten) mice which develop autoimmune disease related to defective Fas apoptosis signaling. Therefore, multiple interactive pathways play a role in limiting development of autoimmunity.

Role of calmodulin in HIV-potentiated Fas-mediated apoptosis

The recently demonstrated extraordinary rate of turnover of T cells in human immunodeficiency virus (HIV)-1-infected patients and the apparently concomitant high rate of viral production and death are consistent with a large amount of cell death directly due to infection. Apoptosis may be one of the major forms of T cell death in HIV-1 infection. Many apoptotic pathways depend on calcium and therefore would be expected to involve calmodulin. As the HIV-1 envelope glycoprotein, gp160, contains two known calmodulin-binding domains, we investigated the possibility that the cytoplasmic domain of the HIV-1 envelope protein gp160 could enhance Fas-mediated apoptosis, the major form of apoptosis in lymphocytes. Our studies have shown that 1) transfection of H9 and MOLT-4 cells with a non-infectious HIV proviral clone, pFN, which expresses wild-type gp160, leads to enhanced Fas-mediated apoptosis, 2) transfection of MOLT-4 cells with a pFN construct pFN delta 147, which expresses a carboxyl-terminally truncated gp160 lacking the calmodulin-binding domains, produces less Fas-mediated apoptosis than transfection with pFN, and 3) the calmodulin antagonists trifluoperazine and tamoxifen completely inhibit the pFN enhancement of Fas-mediated apoptosis in MOLT-4 cells. We have replicated all of these results using the vectors pSRHS and pSRHS delta 147, which express wild-type gp160 and truncated gp160, respectively, in the absence of other viral proteins. These investigations provide a mechanism by which HIV-1 may induce apoptosis and a possible intracellular target for future therapeutics.

The role of programmed cell death as an emerging new concept for the pathogenesis of autoimmune diseases

Activation-induced apoptosis is a primary mechanism for downmodulation of an immune response leading to immune homeostasis and deletion of T cells with specificities which may be harmful. These include deletion of T cells with self-specificities (autospecific) and excessively high affinity for foreign antigen which may lead to an excessively heightened immune response and septic shock. Surface molecules involved in activation-induced apoptosis involve Fas and Fas ligand (FasL), as well as the T-cell receptor (TCR) which modulates the expression and function of these molecules. Fas signaling mechanisms include the hematopoietic cell phosphatase (HCP) and sphingomyelinase, while TCR-signaling mechanisms include Nur77 and fyn kinase and unknown molecules that modulate expression of FasL. Apoptosis signals are further modulated by inhibitors or inducers of apoptosis including Bcl-2, p53, and interleukin-1 beta converting enzyme (ICE). Further understanding of the interaction of these molecules in autoimmune disease may lead to more specific therapies for immunosuppression tailored to the genetic or environmentally induced, activation-induced apoptosis defect in patients.

Inhibition of superantigen-induced proinflammatory cytokine production and inflammatory arthritis in MRL-lpr/lpr mice by a transcriptional inhibitor of TNF-alpha

We have used fas-defective MRL-lpr/lpr mice to study the effects of the staphylococcal enterotoxin superantigens on the development of autoimmune, inflammatory joint disease in animals that are susceptible to the development of rheumatoid arthritis-like disease. We show that systematic administration by a single i.p. injection of staphylococcal enterotoxin B (SEB; 10 micrograms/mouse) caused a mild, inflammatory arthritis +30 days postchallenge in the knee joints of young (< 2-mo-old) MRL-lpr/lpr mice, but not aged-matched MRL +/+ mice. In aged (> 8-mo-old) MRL-lpr/lpr mice, but not in aged MRL +/+ mice, SEB caused a severe, inflammatory arthritis, as assessed histologically, and systemic autoimmune disease, including glomerulonephritis and autoantibody production. Furthermore, in aged MRL-lpr/lpr mice, SEB but not heat-denatured SEB caused acute weight loss and elevated levels of serum proinflammatory cytokines. Compared with highly purified peritoneal macrophages obtained from either aged MRL +/+, young MRL-lpr/lpr, or young MRL +/+, peritoneal macrophages obtained from aged MRL-lpr/lpr mice constitutively expressed 2- to 10-fold greater levels of TNF-alpha, IL-1 beta, IL-6, and IL-10, and produced elevated amounts of these cytokines when treated in vitro with SEB. SEB-challenged aged MRL-lpr/lpr mice treated with anti-TNF mAb (100 micrograms/mouse; every other day), anti-V beta 8 TCR mAb (250 micrograms/mouse; every other day), or orally with the novel TNF-alpha inhibitor MDL 201,449A (9-[(1R, 3R)-trans-cyclopentan-3-ol] adenine; 25 mg/kg/day) exhibited reduced inflammatory arthritis, autoantibody formation, and serum TNF-alpha levels, but not IL-10 levels, after +30 days of treatment. These data suggest that SEB is an extremely potent macrophage-activating factor in vitro and in vivo, enhancing several aspects of autoimmune disease in MRL-lpr/lpr mice, and that anti-TNF therapies may have potential use in inflammatory arthritis.

Inhibition of superantigen-induced proinflammatory cytokine production and inflammatory arthritis in MRL-lpr/lpr mice by a transcriptional inhibitor of TNF-alpha

We have used fas-defective MRL-lpr/lpr mice to study the effects of the staphylococcal enterotoxin superantigens on the development of autoimmune, inflammatory joint disease in animals that are susceptible to the development of rheumatoid arthritis-like disease. We show that systematic administration by a single i.p. injection of staphylococcal enterotoxin B (SEB; 10 micrograms/mouse) caused a mild, inflammatory arthritis +30 days postchallenge in the knee joints of young (&lt; 2-mo-old) MRL-lpr/lpr mice, but not aged-matched MRL +/+ mice. In aged (&gt; 8-mo-old) MRL-lpr/lpr mice, but not in aged MRL +/+ mice, SEB caused a severe, inflammatory arthritis, as assessed histologically, and systemic autoimmune disease, including glomerulonephritis and autoantibody production. Furthermore, in aged MRL-lpr/lpr mice, SEB but not heat-denatured SEB caused acute weight loss and elevated levels of serum proinflammatory cytokines. Compared with highly purified peritoneal macrophages obtained from either aged MRL +/+, young MRL-lpr/lpr, or young MRL +/+, peritoneal macrophages obtained from aged MRL-lpr/lpr mice constitutively expressed 2- to 10-fold greater levels of TNF-alpha, IL-1 beta, IL-6, and IL-10, and produced elevated amounts of these cytokines when treated in vitro with SEB. SEB-challenged aged MRL-lpr/lpr mice treated with anti-TNF mAb (100 micrograms/mouse; every other day), anti-V beta 8 TCR mAb (250 micrograms/mouse; every other day), or orally with the novel TNF-alpha inhibitor MDL 201,449A (9-[(1R, 3R)-trans-cyclopentan-3-ol] adenine; 25 mg/kg/day) exhibited reduced inflammatory arthritis, autoantibody formation, and serum TNF-alpha levels, but not IL-10 levels, after +30 days of treatment. These data suggest that SEB is an extremely potent macrophage-activating factor in vitro and in vivo, enhancing several aspects of autoimmune disease in MRL-lpr/lpr mice, and that anti-TNF therapies may have potential use in inflammatory arthritis.

Hematopoietic cell protein-tyrosine phosphatase-deficient motheaten mice exhibit T cell apoptosis defect

We previously demonstrated that hematopoietic cell protein-tyrosine phosphatase is one of the molecules that can transduce Fas-mediated apoptosis signals in lymphoid cells. The present study analyzed the effect of defective Fas signaling on the T cell phenotype and apoptosis function in hematopoietic cell protein-tyrosine phosphatase-deficient motheaten mice. Viable motheaten (me(v)/me(v)) mice exhibited increased T cell proliferation and defective activation-induced apoptosis of Fas+ T cells in the lymph node, which was not ascribed to defective Fas ligand function. Furthermore, the Fas-mediated apoptosis defect in activated T cells from me(v)/me(v) mice was confirmed by their resistance to anti-Fas-induced apoptosis. No protein tyrosine dephosphorylation signal was delivered after anti-Fas cross-linking in the lymph node cells of me(v)/me(v) mice as revealed by 32Pi labeling of protein phosphatase substrates. The defective activation-induced apoptosis of Fas+ T cells in me(v)/me(v) mice led to lymphadenopathy with an accumulation of CD4- CD8- B220+ CD3+ T cells. Pneumonitis in me(v)/me(v) mice was associated with infiltration of cycling T cells detected by bromodeoxyuridine uptake in vivo. Thus, T cells from me(v)/me(v) mice are resistant to Fas-mediated apoptosis which results in lymphoproliferative disease and tissue infiltration.

Hematopoietic cell protein-tyrosine phosphatase-deficient motheaten mice exhibit T cell apoptosis defect

We previously demonstrated that hematopoietic cell protein-tyrosine phosphatase is one of the molecules that can transduce Fas-mediated apoptosis signals in lymphoid cells. The present study analyzed the effect of defective Fas signaling on the T cell phenotype and apoptosis function in hematopoietic cell protein-tyrosine phosphatase-deficient motheaten mice. Viable motheaten (me(v)/me(v)) mice exhibited increased T cell proliferation and defective activation-induced apoptosis of Fas+ T cells in the lymph node, which was not ascribed to defective Fas ligand function. Furthermore, the Fas-mediated apoptosis defect in activated T cells from me(v)/me(v) mice was confirmed by their resistance to anti-Fas-induced apoptosis. No protein tyrosine dephosphorylation signal was delivered after anti-Fas cross-linking in the lymph node cells of me(v)/me(v) mice as revealed by 32Pi labeling of protein phosphatase substrates. The defective activation-induced apoptosis of Fas+ T cells in me(v)/me(v) mice led to lymphadenopathy with an accumulation of CD4- CD8- B220+ CD3+ T cells. Pneumonitis in me(v)/me(v) mice was associated with infiltration of cycling T cells detected by bromodeoxyuridine uptake in vivo. Thus, T cells from me(v)/me(v) mice are resistant to Fas-mediated apoptosis which results in lymphoproliferative disease and tissue infiltration.

Greatly accelerated lymphadenopathy and autoimmune disease in lpr mice lacking tumor necrosis factor receptor I

Fas and TNF receptor I (TNF-RI) share homology at their cytoplasmic death domain and belong to the same gene family, but utilize different pathways to signal activation-induced cell death. To determine the combined effects of defective TNF-RI and Fas signaling on lymphadenopathy and autoimmune disease, we backcrossed TNF-RI knockout mice (Tnfr1(0/0)) with Fas-deficient C57BL/6-lpr/lpr mice. Tnfr1(0/0)lpr/lpr mice developed greatly accelerated lymphadenopathy and autoantibody production compared with C57BL/6-lpr/ lpr mice. Tnfr1(0/0)-lpr/lpr mice also exhibited high mortality and early onset autoimmune disease characterized by massive mononuclear cell infiltration in liver, kidney, lung, and knee joints. These results indicate that the Fas-mediated apoptosis defect in lpr mice is accelerated in the absence of TNF-RI and that normal expression of TNF-RI might partially compensate for the Fas-mediated apoptosis defect of mononuclear cells in lpr mice.

Greatly accelerated lymphadenopathy and autoimmune disease in lpr mice lacking tumor necrosis factor receptor I

Fas and TNF receptor I (TNF-RI) share homology at their cytoplasmic death domain and belong to the same gene family, but utilize different pathways to signal activation-induced cell death. To determine the combined effects of defective TNF-RI and Fas signaling on lymphadenopathy and autoimmune disease, we backcrossed TNF-RI knockout mice (Tnfr1(0/0)) with Fas-deficient C57BL/6-lpr/lpr mice. Tnfr1(0/0)lpr/lpr mice developed greatly accelerated lymphadenopathy and autoantibody production compared with C57BL/6-lpr/ lpr mice. Tnfr1(0/0)-lpr/lpr mice also exhibited high mortality and early onset autoimmune disease characterized by massive mononuclear cell infiltration in liver, kidney, lung, and knee joints. These results indicate that the Fas-mediated apoptosis defect in lpr mice is accelerated in the absence of TNF-RI and that normal expression of TNF-RI might partially compensate for the Fas-mediated apoptosis defect of mononuclear cells in lpr mice.

Inhibition of Nur77/Nurr1 leads to inefficient clonal deletion of self-reactive T cells

The Nur77/Nurr1 family of DNA binding proteins has been reported to be required for the signal transduction of CD3/T cell receptor (TCR)-mediated apoptosis in T cell hybridomas. To determine the role of this family of DNA-binding proteins in thymic clonal deletion, transgenic (Tg) mice bearing a dominant negative mutation were produced. The transgene consisted of a truncated Nur77 (deltaNur77) gene encoding the DNA-binding domain of Nur77 ligated to a TCR-beta enhancer resulting in early expression in thymocytes. Apoptosis of CD4+CD8+ thymocytes mediated by CD3/TCR signaling was greatly inhibited in the deltaNur77 Tg mice, compared with non-Tg littermates, after treatment with anti-CD3 or anti-TCR antibody in vivo and in vitro. Clonal deletion of self-reactive T cells was investigated in deltaNur77-Db/HY TCR-alpha/beta double Tg mice. There was a five-fold increase in the total number of thymocytes expressing self-reactive Db/HY TCR-alpha/beta in the deltaNur77-TCR-alpha/beta double Tg male mice. Deficient clonal deletion of self-reactive thymocytes was demonstrated by a 10-fold increase in the CD4+CD8+ thymocytes that expressed Tg TCR-alpha/beta. There was an eightfold increase in the CD8+, Db/HY TCR-alpha/beta T cells in the lymph nodes (LN) of delta Nur77-Db/HY TCR-alpha/beta double Tg compared with Db/HY TCR-alpha/beta Tg male mice. In spite of defective clonal deletion, the T cells expressing the Tg TCR were functionally anergic. In vivo analysis revealed increased activation and apoptosis of T cells associated with increased expression of Fas and Fas ligand in LN of deltaNur77-Db/HY TCR-alpha/beta double male mice. These results indicate that inhibition of Nur77/Nurr1 DNA binding in T cells leads to inefficient thymic clonal deletion, but T cell tolerance is maintained by Fas-dependent clonal deletion in LN and spleen.

Increased susceptibility of fas mutant MRL-lpr/lpr mice to staphylococcal enterotoxin B-induced septic shock

MRL-lpr/lpr mice are defective in the fas Ag/APO-1 apoptosis gene (CD95). Using the hepatotoxin D-galactosamine (D-GalNH2), we demonstrate that MRL-lpr/lpr mice have an increased susceptibility to staphylococcal enterotoxin B (SEB)-induced lethal shock, which causes them to exhibit the septic shock-like behaviors of fur ruffling and listlessness, and death occurs within 8 to 18 h. SEB susceptibility is greater in V beta 8.2 TCR transgenic MRL-lpr/lpr mice than in nontransgenic mice. In studies designed to elucidate the molecular pathways of SEB-induced septic shock, we found that C57Bl/6.Ab0/Ab0, MHC class II-deficient "C2D" mice, but not C57Bl/6-(+/+) mice, are nonresponsive to challenge with SEB. C2D mice, backcrossed with the fas mutation resulting in double-knockout C2D;lpr/lpr mice, are more susceptible to challenge with SEB/D-GalNH2. The LD50s for C57Bl/6.C3H-gld/gld "fas ligand-mutant mice" challenged with SEB/D-GalNH2 were comparable to C57Bl/6.MRL-lpr/lpr and MRL-lpr/lpr mice, suggesting that reciprocal mutations in either fas or fas ligand increases susceptibility to bacterial superantigens (SAGs). SEB-induced lethal shock can be reversed by treatment with Abs to V beta 8 TCR, MHC class II Ia+, IL-2, and TNF-alpha, by the immunosuppressant cyclosporin A, or by treatment with carbocyclic nucleoside analogues. These data indicate that SAG-induced septic shock is dependent on interactions with the TCR and MHC class II Ags, and they also suggest a critical role for a functional fas and/or fas ligand in resistance to SAG-induced septic shock.

Increased susceptibility of fas mutant MRL-lpr/lpr mice to staphylococcal enterotoxin B-induced septic shock

MRL-lpr/lpr mice are defective in the fas Ag/APO-1 apoptosis gene (CD95). Using the hepatotoxin D-galactosamine (D-GalNH2), we demonstrate that MRL-lpr/lpr mice have an increased susceptibility to staphylococcal enterotoxin B (SEB)-induced lethal shock, which causes them to exhibit the septic shock-like behaviors of fur ruffling and listlessness, and death occurs within 8 to 18 h. SEB susceptibility is greater in V beta 8.2 TCR transgenic MRL-lpr/lpr mice than in nontransgenic mice. In studies designed to elucidate the molecular pathways of SEB-induced septic shock, we found that C57Bl/6.Ab0/Ab0, MHC class II-deficient "C2D" mice, but not C57Bl/6-(+/+) mice, are nonresponsive to challenge with SEB. C2D mice, backcrossed with the fas mutation resulting in double-knockout C2D;lpr/lpr mice, are more susceptible to challenge with SEB/D-GalNH2. The LD50s for C57Bl/6.C3H-gld/gld "fas ligand-mutant mice" challenged with SEB/D-GalNH2 were comparable to C57Bl/6.MRL-lpr/lpr and MRL-lpr/lpr mice, suggesting that reciprocal mutations in either fas or fas ligand increases susceptibility to bacterial superantigens (SAGs). SEB-induced lethal shock can be reversed by treatment with Abs to V beta 8 TCR, MHC class II Ia+, IL-2, and TNF-alpha, by the immunosuppressant cyclosporin A, or by treatment with carbocyclic nucleoside analogues. These data indicate that SAG-induced septic shock is dependent on interactions with the TCR and MHC class II Ags, and they also suggest a critical role for a functional fas and/or fas ligand in resistance to SAG-induced septic shock.

Interaction of substrate and effector binding sites in the ArsA ATPase

The ars operon of plasmid R773 confers resistance to antimonials and arsenicals in Escherichia coli by encoding an ATP-dependent extrusion system for the oxyanions. The catalytic subunit, the ArsA protein, is an ATPase with two nucleotide binding consensus sequences, one in the N-terminal half and one in the C-terminal half of the protein. The ArsA ATPase is allosterically activated by tricoordinate binding of As(3+) or Sb(3+) to three cysteine thiolates. Previous measurements suggested that the intrinsic fluorescence of tryptophans might be useful for examining binding of Mg2+ ATP and antimonite. In the present study an increase in intrinsic tryptophan fluorescence was observed upon addition of Mg2+ ATP. This enhancement was reversed by addition of antimonite. The ArsA protein contains four tryptophan residues: Trp159, Trp253, Trp522, and Trp524. The first two were altered to tyrosine residues by site-directed mutagenesis. Cells expressing both the arsAW159Y and arsAW253Y mutations retained resistance to arsenite, and the purified W159Y and W253Y proteins retained ATPase activity. While the intrinsic tryptophan fluorescence of the W253Y protein responded to addition of Mg2+ ATP, intrinsic tryptophan fluorescence in the purified W159Y protein was no longer enhanced by substrate. These results suggest that Trp159 is conformationally coupled to one or both of the nucleotide binding sites and provides a useful probe for the interaction of effector and substrate binding sites.