TuJ1 (class III beta-tubulin) expression suggests dynamic redistribution of follicular dendritic cells in lymphoid tissue

Follicular dendritic cells (FDCs) play central roles in the B cell survival, proliferation, and differentiation into memory cells. Here, we show that TuJ1 (class III beta-tubulin) is expressed strongly in FDCs of human lymphoid tissue. TuJ1 has been a marker of neurons in the central and peripheral nervous systems from the early stage of neural differentiation. FDCs expressed TuJ1 protein diffusely in both light and dark zones of germinal centers in all human lymphoid tissues. In contrast, CD21 expression was relatively concentrated to the light zone, suggesting that TuJ1 was a marker for FDCs with broader spectrum than CD21. In addition to the germinal center, there were single TuJ1-expressing cells scattered in the mantle zone, blurring the border of the FDC network. In human tonsils, single scattered TuJ1-positive cells were also present in the crypt epithelium, suggesting a dynamic redistribution of FDCs among the antigen-rich epithelium, mantle zone, and germinal center. Such migration of FDCs could reflect a way of direct transport of various antigens carried on their surface to the germinal center, and a basis for the polarity of lymphoid follicles toward the epithelium in mucosa-associated lymphoid tissues. HK cells, cultured FDCs, also expressed TuJ1. The expression of TuJ1 by FDCs suggests that they may share certain biological characteristics of the neural system.     

Follicular dendritic cell-mediated up-regulation of CXCR4 expression on CD4 T cells and HIV pathogenesis

Follicular dendritic cells (FDCs) represent a major reservoir of HIV, and active infection occurs surrounding these cells, suggesting that this microenvironment is highly conducive to virus transmission. Because CD4 T cells around FDCs in germinal centers express the HIV coreceptor, CXCR4, whereas CD4 lymphocytes in many other sites do not, it prompted the hypothesis that FDCs may increase CXCR4 expression on CD4 T cells, thereby facilitating infection. To test this, HIV receptor/coreceptor expression was determined on CD4 T cells cultured with or without FDCs, and its consequence to infection was assessed by measuring virus binding and entry. FDCs had little effect on CCR5 or CD4 expression but increased CXCR4 expression on CD4 T cells. FDC-mediated up-regulation of CXCR4 on CD4 T cells occurred by 24 h and was sustained for at least 96 h in vitro, and FDC-CD4 T cell contact was necessary. Importantly, increased CXCR4 expression directly correlated with increased binding and entry of HIV-1 X4 isolates. Furthermore, CD4(+)CD57(+) germinal center T cells expressed high levels of CXCR4 and supported enhanced entry of X4 HIV compared with other CD4 T cells from the same tissue. Thus, in addition to serving as a reservoir of infectious virus, FDCs render surrounding germinal center T cells highly susceptible to infection with X4 isolates of HIV-1.     

Human follicular dendritic cells promote the APC capability of B cells by enhancing CD86 expression levels

Follicular dendritic cells (FDCs) are an essential cellular component of the germinal center (GC) and are believed to exert regulatory effects on the various stages of GC reactions. According to our previous reports, human FDCs express prostacyclin synthase, and prostacyclin analogues augment adhesion and co-stimulatory molecules on the surface of activated B cells. These findings prompted us to investigate whether FDCs would contribute to the antigen-presenting capability of B cells by using the well-established FDC-like cells, HK cells, and tonsillar B cells. Our results show that HK cells significantly enhance the expression levels of CD54, CD80, and CD86 on the surface of activated B cells. The enhancing effect of HK cells on CD86 is impeded by indomethacin and an EP4 antagonist, implying that a certain prostaglandin is mediating the up-regulation. Prostacyclin indeed recapitulates the enhancing effect on CD86, which is inhibited by EP4 as well as IP antagonists. B cells co-cultured with HK cells exhibit an augmented APC activity, which is inhibited by CD86 neutralization. These results reveal another unrecognized function of human FDC.     

Functional effects of TNF-alpha on a human follicular dendritic cell line: persistent NF-kappa B activation and sensitization for Fas-mediated apoptosis

Follicular dendritic cells (FDC) play crucial roles in germinal center (GC) formation and differentiation of GC B cells. FDC functions are influenced by cytokines produced in the GC. Among the GC cytokines, TNF is known to be essential for the formation and maintenance of the FDC network in the GC. We found that TNF is a mitogenic growth factor to an established FDC-like cell line, HK cells. Differing from most cell types which become desensitized to TNF action, HK cells exhibited persistent TNF signaling, as demonstrated by prolonged and biphasic NF-kappaB activation even after 3 days of TNF treatment. As a result, antiapoptotic genes including TNFR-associated factors 1 and 2, and cellular inhibitor of apoptosis proteins 1 and 2 were persistently induced by TNF, leading to the protection against TNF-mediated cell death. However, TNF pretreatment enhanced Fas-mediated apoptosis by up-regulating surface Fas expression in an NF-kappaB-dependent pathway. During the GC responses, proliferation followed by FDC death has not been documented. However, our in vitro results suggest that FDCs proliferate in response to TNF, and die by Fas-mediated apoptosis whose susceptibility is enhanced by TNF, representing a mode of action for TNF in the maintenance of FDC networks by regulating the survival or death of FDC.     

Subpopulations of B lymphocytes in germinal centers

With two new monoclonal antibodies and flow cytometry, we defined three subpopulations among B cells expressing binding sites for peanut agglutinin (i.e., B cells of the germinal center). On monoclonal antibody (5B5) binds globotriaosyl ceramide. The B lymphocytes binding 5B5 have binding sites for peanut agglutinin on the surface and express only small amounts of sIgD and sIgM. When tested against a panel of B cell lines, only Burkitt's lymphoma cells were 5B5+. Moreover, the 5B5+ cells have larger average sizes and a large fraction of proliferating cells. The other monoclonal antibody (HK23) binds a 90,000 protein. Lymphocytes binding HK23 are 5B5- and include T cells and a subpopulation of B cells. In contrast to 5B5+ cells, the HK23+ and peanut agglutinin positive B cells express a large amount of sIgM. These two subpopulations of germinal centers are distinct from the germinal center B cell subpopulation expressing the CD23 (Blast-2) antigen. The CD23+ B cells are 5B5- and express an intermediate level of HK23 antigen. In addition, CD23+ B cells are highly variable in number, whereas the proportions of HK23+ and 5B5+ cells are relatively stable.     

Follicular dendritic cell regulation of CXCR4-mediated germinal center CD4 T cell migration

Follicular dendritic cells (FDCs) up-regulate the chemokine receptor CXCR4 on CD4 T cells, and a major subpopulation of germinal center (GC) T cells (CD4(+)CD57(+)), which are adjacent to FDCs in vivo, expresses high levels of CXCR4. We therefore reasoned that GC T cells would actively migrate to stromal cell-derived factor-1 (CXCL12), the CXCR4 ligand, and tested this using Transwell migration assays with GC T cells and other CD4 T cells (CD57(-)) that expressed much lower levels of CXCR4. Unexpectedly, GC T cells were virtually nonresponsive to CXCL12, whereas CD57(-)CD4 T cells migrated efficiently despite reduced CXCR4 expression. In contrast, GC T cells efficiently migrated to B cell chemoattractant-1/CXCL13 and FDC supernatant, which contained CXCL13 produced by FDCs. Importantly, GC T cell nonresponsiveness to CXCL12 correlated with high ex vivo expression of regulator of G protein signaling (RGS), RGS13 and RGS16, mRNA and expression of protein in vivo. Furthermore, FDCs up-regulated both RGS13 and RGS16 mRNA expression in non-GC T cells, resulting in their impaired migration to CXCL12. Finally, GC T cells down-regulated RGS13 and RGS16 expression in the absence of FDCs and regained migratory competence to CXCL12. Although GC T cells express high levels of CXCR4, signaling through this receptor appears to be specifically inhibited by FDC-mediated expression of RGS13 and RGS16. Thus, FDCs appear to directly affect GC T cell migration within lymphoid follicles.     

Modulation of the fibrinolytic response of cultured human vascular endothelium by extracellularly generated oxygen radicals.

Clinical and experimental data indicate that activated oxygen species interfere with vascular endothelial cell function. Here, the impact of extracellular oxidant injury on the fibrinolytic response of cultured human umbilical vein endothelial (HUVE) cells was investigated at the protein and mRNA levels. Xanthine (50 microM) and xanthine oxidase (100 milliunits), which produces the superoxide anion radical (O2-) and hydrogen peroxide (H2O2), was used to sublethally injure HUVE cells. Following a 15-min exposure, washed cells were incubated for up to 24 h in serum-free culture medium. Tissue-type plasminogen activator (t-PA) antigen, plasminogen activator inhibitor-1 (PAI-1) antigen, and PAI-1 activity were determined in 1.25 ml of conditioned medium and t-PA and PAI-1 mRNA in the cell extracts of 2 x 10(6) HUVE cells. Control cells secreted 3.9 +/- 1.3 ng/ml (mean +/- S.D., n = 12) within 24 h. Treatment with xanthine/xanthine oxidase for 15 min induced a 2.8 +/- 0.4-fold increase (n = 12, p less than 0.05) of t-PA antigen secretion after 24 h. The t-PA antigen was recovered predominantly in complex with PAI-1. The oxidant injury caused a 3.0 +/- 0.8-fold increase (n = 9, p less than 0.05) in t-PA mRNA within 2 h. Total protein synthesis was unaltered by xanthine/xanthine oxidase. The oxidant scavengers superoxide dismutase and catalase, in combination, abolished the effect of xanthine/xanthine oxidase on t-PA secretion and t-PA mRNA synthesis. Xanthine/xanthine oxidase treatment of HUVE cells did not affect the PAI-1 secretion in conditioned medium nor the PAI-1 mRNA levels in cell extracts. Thus extracellular oxidant injury induces t-PA but not PAI-1 synthesis in HUVE cells.     

TGF-beta inhibits Fas-mediated apoptosis of a follicular dendritic cell line by down-regulating the expression of Fas and caspase-8: counteracting role of TGF-beta on TNF sensitization of Fas-mediated apoptosis

Follicular dendritic cells (FDC) constitute the framework of germinal center (GC) in secondary lymphoid follicles, and the integrity of FDC networks is critically affected by cytokines present in the GC. We have previously shown that TNF promotes Fas-mediated apoptosis of HK cells, an established FDC-like cell line, by up-regulating Fas expression. However, in the developing GC, FDC death is not a hallmark of GC despite the presence of TNF and FasL. In this study, we report that TGF-beta inhibits Fas-mediated apoptosis of HK cells by down-regulating the expression of surface Fas and caspase-8. The inhibitory effect of TGF-beta can be observed when HK cells were simultaneously treated with TNF and TGF-beta, indicating that TGF-beta counteracts the effect of TNF in sensitizing cells to Fas-mediated apoptosis. Furthermore, the deprivation of TGF-beta by injecting neutralizing TGF-beta Abs to the SRBC-immunized mice resulted in the sporadic appearance of FDC undergoing apoptosis in the lymphoid follicles, suggesting that TGF-beta functions as a naturally occurring inhibitor that rescues FDCs which are predisposed to apoptosis. Our study documents a novel function of TGF-beta in the maintenance of FDC networks.     

Purification and immunochemical studies of pyruvate dehydrogenase complex from rat heart, and cell-free synthesis of lipoamide dehydrogenase, a component of the complex

A mixture of NADPH and ferredoxin reductase is a convenient way of reducing adriamycin in vitro. Under aerobic conditions the adriamycin semiquinone reacts rapidly with O2 and superoxide radical is produced. Superoxide generated either by adriamycin:ferredoxin reductase or by hypoxanthine:xanthine oxidase can promote the formation of hydroxyl radicals in the presence of soluble iron chelates. Hydroxyl radicals produced by a hypoxanthine:xanthine oxidase system in the presence of an iron chelate cause extensive fragmentation in double-stranded DNA. Protection is offered by catalase, superoxide dismutase or desferrioxamine. Addition of double-stranded DNA to a mixture of adriamycin, ferredoxin reductase, NADPH and iron chelate inhibits formation of both superoxide and hydroxyl radicals. This is not due to direct inhibition of ferredoxin reductase and single-stranded DNA has a much weaker inhibitory effect. It is concluded that adriamycin intercalated into DNA cannot be reduced.     

Redox cycling of potential antitumor aziridinyl quinones

The formation of reactive oxygen intermediates (ROI) during redox cycling of newly synthesized potential antitumor 2,5-bis (1-aziridinyl)-1,4-benzoquinone (BABQ) derivatives has been studied by assaying the production of ROI (superoxide, hydroxyl radical, and hydrogen peroxide) by xanthine oxidase in the presence of BABQ derivatives. At low concentrations (< 10 microM) some BABQ derivatives turned out to inhibit the production of superoxide and hydroxyl radicals by xanthine oxidase, while the effect on the xanthine-oxidase-induced production of hydrogen peroxide was much less pronounced. Induction of DNA strand breaks by reactive oxygen species generated by xanthine oxidase was also inhibited by BABQ derivatives. The DNA damage was comparable to the amount of hydroxyl radicals produced. The inhibiting effect on hydroxyl radical production can be explained as a consequence of the lowered level of superoxide, which disrupts the Haber-Weiss reaction sequence. The inhibitory effect of BABQ derivatives on superoxide formation correlated with their one-electron reduction potentials: BABQ derivatives with a high reduction potential scavenge superoxide anion radicals produced by xanthine oxidase, leading to reduced BABQ species and production of hydrogen peroxide from reoxidation of reduced BABQ. This study, using a unique series of BABQ derivatives with an extended range of reduction potentials, demonstrates that the formation of superoxide and hydroxyl radicals by bioreductively activated antitumor quinones can in principle be uncoupled from alkylating activity.     

Effect of zinc on superoxide-dependent hydroxyl radical production in vitro

Trace elements play an important role in oxygen metabolism and therefore in the formation of free radicals. Whereas iron and copper are usually the main enhancers of free radical formation, other trace elements, such as zinc and selenium, protect against the harmful effects of these radicals. To investigate the different protective mechanisms of zinc on radical formation, we examined the effects of added zinc and copper on superoxide dismutase activity. We also studied the effects of copper and iron on xanthine oxidase activity and on the Haber-Weiss cycle (iron, superoxide, and hydrogen peroxide), which generates hydroxyl radicals in vitro. The hypoxanthine/xanthine oxidase radical generating system contained a variety of different physiological ligands for binding the iron. This study confirmed the inhibitory effect of copper on xanthine oxidase activity. Moreover, it demonstrated that zinc inhibited hydroxyl radical formation when this formation was catalyzed by a citrate-iron complex in the hypoxanthine/xanthine oxidase reaction. Finally, human blood plasma inhibited citrate-iron-dependent hydroxyl radical formation under the same conditions. Although trace elements seemed responsible for this antioxidant activity of plasma, it is likely that zinc played no role as a plasma antioxidant. Indeed, calcium appeared to be responsible for most of this effect under our experimental conditions.     

Glutamate Neurotoxicity in Rat Cerebellar Granule Cells: A Major Role for Xanthine Oxidase in Oxygen Radical Formation

Abstract: To gain insight into the mechanism through which the neurotransmitter glutamate causally participates in several neurological diseases, in vitro cultured cerebellar granule cells were exposed to glutamate and oxygen radical production was investigated. To this aim, a novel procedure was developed to detect oxygen radicals; the fluorescent dye 2',7'-dichlorofluorescein was used to detect production of peroxides, and a specific search for the possible conversion of the enzyme xanthine dehydrogenase into xanthine oxidase after the excitotoxic glutamate pulse was undertaken. A 100 µ M glutamate pulse administered to 7-day-old cerebellar granule cells is accompanied by the onset of neuronal death, the appearance of xanthine oxidase, and production of oxygen radicals. Xanthine oxidase activation and superoxide (O₂^•−) production are completely inhibited by concomitant incubation of glutamate with MK-801, a specific NMDA receptor antagonist, or by chelation of external calcium with EGTA. Partial inhibition of both cell death and parallel production of reactive oxygen species is achieved with allopurinol, a xanthine oxidase inhibitor, leupeptin, a protease inhibitor, reducing agents such as glutathione or dithiothreitol, antioxidants such as vitamin E and vitamin C, and externally added superoxide dismutase. It is concluded that glutamate-triggered, NMDA-mediated, massive Ca²⁺ influx induces rapid conversion of xanthine dehydrogenase into xanthine oxidase with subsequent production of reactive oxygen species that most probably have a causal involvement in the initial steps of the series of intracellular events leading to neuronal degeneration and death.     

Quantitation of intracellular oxidation in a renal epithelial cell line

We quantitated the presence of intracellular oxidizing species in response to oxidative stimuli using fluorescent cell analytic techniques. The studies were performed with a laser-activated flow cytometry system using 2',7'-dichlorofluorescin diacetate (DCFDA) as a probe for intracellular oxidation events. Oxygen radical formation was initiated by the addition of FeCl2 or xanthine oxidase to the culture media. Xanthine oxidase and FeCl2 both increased intracellular DCFDA oxidation over control (p less than .001). Increases in intracellular DCFDA oxidation in response to xanthine oxidase exposure were inhibited by extracellular superoxide dismutase, catalase and dimethyl sulfoxide (p less than 0.001), implicating the superoxide anion, hydrogen peroxide, and the hydroxyl radical in producing the changes in intracellular dichlorofluorescein fluorescence. Increases in intracellular DCFDA oxidation in response to xanthine oxidase correlated with loss of cellular viability, as established by decreased plating efficiency. We conclude that relative intracellular oxidation can be quantitated within the cultured renal cell and that some extracellularly generated radicals may be capable of traversing the intact cell membrane to oxidize DCFDA in the cell interior.     

Effects of oxygen radicals on substrate oxidation by cardiac myocytes

Freshly isolated adult rat heart cells were used to study the effects of oxygen-free radicals on the myocardial oxidation of different substrates. The calcium-tolerant quiescent cells were incubated with xanthine plus xanthine oxidase as the source of free radicals. The oxidation of exogenous glucose, lactate and octanoate was severely inhibited (approx. 70%) by products of xanthine oxidase activity. Superoxide dismutase plus catalase effectively prevented the inhibition of oxidation. Cellular high energy phosphate levels were decreased in the presence of the oxygen free radical generating system although cell viability determined by Trypan blue exclusion and light microscopic assessment of normal morphology was not affected. These data suggest that oxygen free radicals decrease myocardial substrate oxidation which may contribute to the functional and ultrastructural changes in the myocardium under conditions such as reoxygenation after hypoxia and reperfusion after ischemia.     

DNA damage by superoxide-generating systems in relation to the mechanism of action of the anti-tumour antibiotic adriamycin

1. A mixture of NADPH and ferrodoxin reductase is a convenient way of reducing adriamycin in vitro. Under aerobic conditions the adriamycin semiquinone reacts rapidly with O₂ and superoxide radical is produced. 2. Superoxide generated either by adriamycin:ferredoxin reductase or by hypoxanthine: xanthine oxidase can promote the formation of hydroxyl radicals in the presence of soluble iron chelates. 3. Hydroxyl radicals produced by a hypoxanthine:xanthine oxidase system in the presence of an iron chelate cause extensive fragmentation in double-stranded DNA. Protection is offered by catalase, superoxide dismutase or desferrioxamine. 4. Addition of double-stranded DNA to a mixture of adriamycin, ferredoxin reductase, NADPH and iron chelate inhibits formation of both superoxide and hydroxyl radicals. This is not due to direct inhibition of ferredoxin reductase and single-stranded DNA has a much weaker inhibitory effect. It is concluded that adriamycin intercalated into DNA cannot be reduced.     

Role of metabolism pathway interaction of formaldehyde and nitric oxide in the mechanism of their toxic effect. 2. Toxic effect of nitric oxide

Toxic properties of NO in organism are realized under its hyperproduction and inhibition of the system of anti-oxidant protection as a result of complex chemical transformations, the transient metals, oxygen, superoxide and other radicals being their main participant. Here direct paths (through formation of nitrosil complexes with the gem and nongem iron) of the toxic action of NO and the path mediated by active forms of nitrogen are found, which disturb various biomolecules and subcellular component through the reactions of S- and N-nitrozation, nitration, oxidation, desamination and other reaction, cause metabolic disbalance and death of cells by the type of apoptosis or necrosis. A possible mechanism of the death of cells caused by NO was considered on the example of thymocytes. According to this mechanism one of early stages of this death is a decrease of the cell fund of AP, intensification of catabolism of adenine nucleotides and transformation of xanthine oxidoreductase from D-form (xanthine dehydrogenase) of O-forms (xantine oxidase) which catalizes formation of cytotoxic molecules of superoxide and hydroperoxide. This cytotoxic mechanism which includes transformation of xanthine oxidase system, is probably, universal and does not depend essentially on the starting factor.     

Superoxide, nitric oxide, peroxynitrite and cytokine combinations all cause functional impairment and morphological changes in rat islets of Langerhans and insulin secreting cell lines, but dictate cell death by different mechanisms

We have shown that nitric oxide treatment for 30–90 min causes inhibition of insulin secretion, DNA damage and disturbs sub-cellular organization in rat and human islets of Langerhans and HIT-T15 cells. Here rat islets and beta-cell lines were treated with various free radical generating systems S-nitrosoglutathione (nitric oxide), xanthine oxidase plus hypoxanthine (reactive oxygen species), 3-morpholinosydnonimine (nitric oxide, super-oxide, peroxynitrite, hydrogen peroxide) and peroxynitrite and their effects over 4 h to 3 days compared with those of the cytokine combination interleukin-1, tumour necrosis factor- and interferon-. End points examined were de novo protein synthesis, cellular reducing capacity, morphological changes and apoptosis by acridine orange cytochemistry, DNA gel electrophoresis and electron microscopy. Treatment (24–72 h) with nitric oxide, superoxide, peroxynitrite or combined cytokines differentially decreased redox function and inhibited protein synthesis in rat islets of Langerhans and in insulin-containing cell lines; cytokine effects were arginine and nitric oxide dependent. Peroxynitrite gave rare apoptosis in HIT-T15 cells and superoxide gave none in any cell type, but caused the most beta cell-specific damage in islets. S-nitroso-glutathione was the most effective agent at causing DNA laddering or chromatin margination characteristic of apoptotic cell death in insulin-containing cells. Cytokine-induced apoptosis was observed specifically in islet beta cells, combined cytokine effects on islet function and death most resembled those of the mixed radical donor SIN-1.     

Suppression of IgE responses in CD23-transgenic animals is due to expression of CD23 on nonlymphoid cells

Serum IgE is suppressed in CD23-transgenic (Tg) mice where B cells and some T cells express high levels of CD23, suggesting that CD23 on B and T cells may cause this suppression. However, when Tg B lymphocytes were compared with controls in B cell proliferation and IgE synthesis assays, the two were indistinguishable. Similarly, studies of lymphokine production suggested that T cell function in the Tg animals was normal. However, adoptive transfer studies indicated that suppression was seen when normal lymphocytes were used to reconstitute Tg mice, whereas reconstitution of controls with Tg lymphocytes resulted in normal IgE responses, suggesting that critical CD23-bearing cells are irradiation-resistant, nonlymphoid cells. Follicular dendritic cells (FDC) are irradiation resistant, express surface CD23, and deliver iccosomal Ag to B cells, prompting us to reason that Tg FDC may be a critical cell. High levels of transgene expression were observed in germinal centers rich in FDC and B cells, and IgE production was inhibited when Tg FDCs were cultured with normal B cells. In short, suppressed IgE production in CD23-Tg mice appears to be associated with a population of radioresistant nonlymphoid cells. FDCs that interface with B cells in the germinal center are a candidate for explaining this CD23-mediated IgE suppression.     

The mechanism of alloxan and streptozotocin action in B cells of the rat pancreas

Alloxan and streptozotocin are widely used to induce experimental diabetes in animals. The mechanism of their action in B cells of the pancreas has been intensively investigated and now is quite well understood. The cytotoxic action of both these diabetogenic agents is mediated by reactive oxygen species, however, the source of their generation is different in the case of alloxan and streptozotocin. Alloxan and the product of its reduction, dialuric acid, establish a redox cycle with the formation of superoxide radicals. These radicals undergo dismutation to hydrogen peroxide. Thereafter highly reactive hydroxyl radicals are formed by the Fenton reaction. The action of reactive oxygen species with a simultaneous massive increase in cytosolic calcium concentration causes rapid destruction of B cells. Streptozotocin enters the B cell via a glucose transporter (GLUT2) and causes alkylation of DNA. DNA damage induces activation of poly ADP-ribosylation, a process that is more important for the diabetogenicity of streptozotocin than DNA damage itself. Poly ADP-ribosylation leads to depletion of cellular NAD+ and ATP. Enhanced ATP dephosphorylation after streptozotocin treatment supplies a substrate for xanthine oxidase resulting in the formation of superoxide radicals. Consequently, hydrogen peroxide and hydroxyl radicals are also generated. Furthermore, streptozotocin liberates toxic amounts of nitric oxide that inhibits aconitase activity and participates in DNA damage. As a result of the streptozotocin action, B cells undergo the destruction by necrosis.     

Sepsis induces apoptosis and profound depletion of splenic interdigitating and follicular dendritic cells

Dendritic cells are a phenotypically diverse group of APC that have unique capabilities to regulate the activity and survival of B and T cells. Although proper function of dendritic cells is essential to host control of invading pathogens, few studies have examined the impact of sepsis on dendritic cells. The purpose of this study was to determine the effect of sepsis on splenic interdigitating dendritic cells (IDCs) and follicular dendritic cells (FDCs) using a clinically relevant animal model. Immunohistochemical staining for FDCs showed that sepsis induced an initial marked expansion in FDCs that peaked at 36 h after onset. The FDCs expanded to fill the entire lymphoid zone otherwise occupied by B cells. Between 36 and 48 h after sepsis, there was a profound caspase 3 mediated apoptosis induced depletion of FDCs such that only a small contingent of cells remained. In contrast to the initial increase in FDCs, IDC numbers were decreased to approximately 50% of control by 12 h after onset of sepsis. IDC death occurred by caspase 3-mediated apoptosis. Such profound apoptosis induced loss of FDCs and IDCs may significantly compromise B and T cell function and impair the ability of the host to survive sepsis.