N-acetylcysteine replenishes glutathione in HIV infection

BACKGROUND

Glutathione (GSH) deficiency is common in HIV-infected individuals and is associated with impaired T cell function and impaired survival. N-acetylcysteine (NAC) is used to replenish GSH that has been depleted by acetaminophen overdose. Studies here test oral administration of NAC for safe and effective GSH replenishment in HIV infection.

DESIGN

Oral NAC administration in a randomized, 8-week double-blind, placebo-controlled trial followed by optional open-label drug for up to 24 weeks.

SUBJECTS

HIV-infected, low GSH, CD4 T cells < 500 micro L(-1), no active opportunistic infections or other debilitation; n = 81. Study conducted prior to introduction of protease inhibitors.

RESULTS

Whole blood GSH levels in NAC arm subjects significantly increased from 0.88 mM to 0.98 mM, bringing GSH levels in NAC-treated subjects to 89% of uninfected controls (P = 0.03). Baseline GSH levels in the placebo group (0.91) remained essentially the same during the 8 week placebo-controlled trial. T cell GSH, adjusted for CD4 T cell count and beta2-microglobulin levels, also increased in the NAC-treated subjects (P = 0.04). Adverse effects were minimal and not significantly associated with NAC ingestion.

CONCLUSION

NAC treatment for 8 weeks safely replenishes whole blood GSH and T cell GSH in HIV-infected individuals. Thus, NAC offers useful adjunct therapy to increase protection against oxidative stress, improve immune system function and increase detoxification of acetaminophen and other drugs. These findings suggest that NAC therapy could be valuable in other clinical situations in which GSH deficiency or oxidative stress plays a role in disease pathology, e.g. rheumatoid arthritis, Parkinson's disease, hepatitis, liver cirrhosis, septic shock and diabetes.

Monoclonal antibodies and the FACS: complementary tools for immunobiology and medicine

The histories of monoclonal antibodies and the fluorescence activated cell sorter (FACS) are as closely intertwined as their current uses in biology and medicine. Here, Leonore Herzenberg, Stephen De Rosa and Leonard Herzenberg recount the meeting and the mating of these two technologies, whose offspring now populate clinical and research laboratories throughout the world.

B-1 and B-2 cell-derived immunoglobulin M antibodies are nonredundant components of the protective response to influenza virus infection

We have studied the role of secreted immunoglobulin (Ig)M in protection from infection with influenza virus and delineated the relative contributions of B-1 versus B-2 cell-derived IgM in this process. Mice deficient in secreted IgM but capable of expressing surface IgM and secreting other Ig classes show significantly reduced virus clearance and survival rates compared with wild-type controls. Irradiation chimeras in which only either B-1 or B-2 cells lack the ability to secrete IgM show mortality rates similar to those of mice in which neither B-1 nor B-2 cells secrete IgM. Dependence on both sources of IgM for survival is partially explained by findings in allotype chimeras that broadly cross-reactive B-1 cell-derived natural IgM is present before infection, whereas virus strain-specific, B-2 cell-derived IgM appears only after infection. Furthermore, lack of IgM secreted from one or both sources significantly impairs the antiviral IgG response. Reconstitution of chimeras lacking B-1 cell-derived IgM only with IgM-containing serum from noninfected mice improved both survival rates and serum levels of virus-specific IgG. Thus, virus-induced IgM must be secreted in the presence of natural IgM for efficient induction of specific IgG and for immune protection, identifying B-1 and B-2 cell-derived IgM antibodies as nonredundant components of the antiviral response.

CD4+ T cells derived from B cell-deficient mice inhibit the establishment of peripheral B cell pools

We demonstrate that adoptive transfer of peritoneal cavity B cells fails to replenish the peripheral B-1 cells in adult B cell-deficient (mu(-/-)) mice but does replenish adult RAG-1(-/-) mice. We show that this lack of self-replenishment in mu(-/-) mice is mediated by strongly inhibitory, radiation-sensitive CD4(+) T cells that also function in cotransfer studies to block the reconstitution of B-1 cells and inhibit accumulation of bone marrow-derived B-2 cells in the periphery in irradiated recipients. CD8(+) T cells from mu(-/-) do not mediate this inhibition. The inhibitory CD4(+) T cells develop early in life, because B-1 cell replenishment occurs normally when B-1 cells are transferred into mu(-/-) neonates. Thus, we conclude that the presence of B cells in the neonate conditions the CD4(+) T-cell population to permit the establishment and maintenance of normal B cell pools throughout life.

Gene microarray identification of redox and mitochondrial elements that control resistance or sensitivity to apoptosis

Multigenic programs controlling susceptibility to apoptosis in response to ionizing radiation have not yet been defined. Here, using DNA microarrays, we show gene expression patterns in an apoptosis-sensitive and apoptosis-resistant murine B cell lymphoma model system both before and after irradiation. From the 11,000 genes interrogated by the arrays, two major patterns emerged. First, before radiation exposure the radioresistant LYar cells expressed significantly greater levels of message for several genes involved in regulating intracellular redox potential. Compared with LYas cells, LYar cells express 20- to 50-fold more mRNA for the tetraspanin CD53 and for fructose-1,6-bisphosphatase. Expression of both of these genes can lead to the increase of total cellular glutathione, which is the principle intracellular antioxidant and has been shown to inhibit many forms of apoptosis. A second pattern emerged after radiation, when the apoptosis-sensitive LYas cells induced rapid expression of a unique cluster of genes characterized by their involvement in mitochondrial electron transport. Some of these genes have been previously recognized as proapoptotic; however others, such as uncoupling protein 2, were not previously known to be apoptotic regulatory proteins. From these observations we propose that a multigenic program for sensitivity to apoptosis involves induction of transcripts for genes participating in mitochondrial uncoupling and loss of membrane potential. This program triggers mitochondrial release of apoptogenic factors and induces the "caspase cascade." Conversely, cells resistant to apoptosis down-regulate these biochemical pathways, while activating pathways for establishment and maintenance of high intracellular redox potential by means of elevated glutathione.

Differential representations of memory T cell subsets are characteristic of polarized immunity in leprosy and atopic diseases

We identified functionally polarized subsets of CD4 memory T cells on the basis of the expression of CD11a, CD45RA and CD62L. Within the several phenotypically distinct subsets of CD4 memory cells are two that, upon stimulation, produce primarily IL-4 (MT(2), CD45RA(-)CD62L(+)CD11a(dim)) or primarily IFN-gamma (MT(1), CD45RA(-)CD62L(-)CD11a(bright)). In addition, four other phenotypically distinct subsets of CD4 cells have unique cytokine profiles. To determine the clinical relevance of the representation of these cell types, we analyzed blood from patients with the chronic diseases leprosy and atopy. These diseases are characterized as immunologically polarized, since T cell responses in affected individuals are often strongly biased towards T(h)1 (dominated by IFN-gamma production) or T(h)2 (IL-4 production). We show here that this polarization reflects homeostatic or differentiation mechanisms affecting the representation of the functionally distinct subsets of memory CD4 T cells, MT(1) and MT(2). Significantly, the representation of the MT(1) and MT(2) subsets differs dramatically between subjects with tuberculoid leprosy (a T(h)1 disease), or lepromatous leprosy or atopic disease (T(h)2 diseases). However, there was no difference in the cytokine profiles of these or any of the other finely resolved CD4 subsets, when compared between individuals across all disease states. Thus, it is the representation of these subsets in peripheral blood that is diagnostic of the polarized state of the immune system.

Thioredoxin, a redox enzyme released in infection and inflammation, is a unique chemoattractant for neutrophils, monocytes, and T cells

Thioredoxin (Trx) is a ubiquitous intracellular protein disulfide oxidoreductase with a CXXC active site that can be released by various cell types upon activation. We show here that Trx is chemotactic for monocytes, polymorphonuclear leukocytes, and T lymphocytes, both in vitro in the standard micro Boyden chamber migration assay and in vivo in the mouse air pouch model. The potency of the chemotactic action of Trx for all leukocyte populations is in the nanomolar range, comparable with that of known chemokines. However, Trx does not increase intracellular Ca2+ and its activity is not inhibited by pertussis toxin. Thus, the chemotactic action of Trx differs from that of known chemokines in that it is G protein independent. Mutation of the active site cysteines resulted in loss of chemotactic activity, suggesting that the latter is mediated by the enzyme activity of Trx. Trx also accounted for part of the chemotactic activity released by human T lymphotropic virus (HTLV)-1-infected cells, which was inhibited by incubation with anti-Trx antibody. Since Trx production is induced by oxidants, it represents a link between oxidative stress and inflammation that is of particular interest because circulating Trx levels are elevated in inflammatory diseases and HIV infection.

Nine color eleven parameter immunophenotyping using three laser flow cytometry

BACKGROUND

This study describes a three laser flow cytometer, reagents, and software used to simultaneously evaluate nine distinct fluorescent parameters on one cell sample. We compare the quality of data obtained with (1) full software compensation and (2) the use of partial spectral compensation of selected pairs of parameters in analog hardware, in combination with final software compensation. An application characterizing low frequency murine B cell subpopulations is given.

METHODS

The fluorochromes used are: fluorescein (FITC), phycoerythrin (PE), Cy5PE and Cy7PE, excited at 488 nm by an argon laser; Texas Red (TR), allophycocyanin (APC), and Cy7APC excited at 595 nm by a pumped dye laser; and cascade blue (CB) and cascade yellow (CY) excited at 407 nm by a violet-enhanced krypton laser. Custom additions to commercial electronics and an extended optical bench allow the measurement of these nine parameters plus forward and side scatter light signals.

RESULTS

We find the use of partial analog compensation reduces the variation in the background staining levels introduced by the compensation process. Novel B cell populations with frequencies below 1% are characterized.

CONCLUSIONS

Nine color flow cytometry is capable of providing measurements with high information content. The choice of reagent-dye combinations and the ability to compensate in multi-parameter measurement space are crucial to obtaining satisfactory results.

Predominant VH genes expressed in innate antibodies are associated with distinctive antigen-binding sites

Antibodies to phosphatidylcholine (PtC), a common constituent of mammalian and bacterial cell membranes, represent a large proportion of the natural antibody repertoire in mice. Previous studies of several mouse strains (e.g., C57BL/6) have shown that anti-PtC antibodies are mainly encoded by the VH11 and VH12 immunoglobulin heavy chain variable region gene families. We show here, however, that VH11 and VH12 encode only a small proportion of the anti-PtC antibodies in BALB/c mice. Instead, VHQ52-encoded antibodies predominate in this strain. In addition, two-thirds of the cells expressing VHQ52 family genes use a single gene (which, interestingly, has been previously shown to predominate in the anti-oxazolone response). We also show here that in anti-PtC antibodies from all strains, the distinctive antigen-binding sites associated with VHQ52 differ substantially from those associated with VH11 and VH12. That is, VHQ52-containing transcripts preferentially use the joining region JH4 rather than JH1 and exhibit more diverse complementarity-determining region 3 (CDR3) junctions with more N-region nucleotide additions at the gene segment junctions. Thus, the VH gene family that predominates in the anti-PtC repertoire differs among mouse strains, whereas the distinctive VHDJH rearrangements (CDR3, JH) associated with each VH gene family are similar in all strains. We discuss these findings in the context of a recent hypothesis suggesting that CDR3 structure, independent of VH framework, is sufficient to define the specificity of an antibody.

Innate and acquired humoral immunities to influenza virus are mediated by distinct arms of the immune system

"Natural" Igs, mainly IgM, comprise part of the innate immune system present in healthy individuals, including antigen-free mice. These Igs are thought to delay pathogenicity of infecting agents until antigen-induced high affinity Igs of all isotypes are produced. Previous studies suggested that the acquired humoral response arises directly from the innate response, i.e., that B cells expressing natural IgM, upon antigen encounter, differentiate to give rise both to cells that secrete high amounts of IgM and to cells that undergo affinity maturation and isotype switching. However, by using a murine model of influenza virus infection, we demonstrate here that the B cells that produce natural antiviral IgM neither increase their IgM production nor undergo isotype switching to IgG2a in response to the infection. These cells are distinct from the B cells that produce the antiviral response after encounter with the pathogen. Our data therefore demonstrate that the innate and the acquired humoral immunities to influenza virus are separate effector arms of the immune system and that antigen exposure per se is not sufficient to increase natural antibody production.

Single cell analysis and selection of living retrovirus vector-corrected mucopolysaccharidosis VII cells using a fluorescence-activated cell sorting-based assay for mammalian beta-glucuronidase enzymatic activity

Mutations in the acid beta-glucuronidase gene lead to systemic accumulation of undegraded glycosaminoglycans in lysosomes and ultimately to clinical manifestations of mucopolysaccharidosis VII (Sly disease). Gene transfer by retrovirus vectors into murine mucopolysaccharidosis VII hematopoietic stem cells or fibroblasts ameliorates glycosaminoglycan accumulation in some affected tissues. The efficacy of gene therapy for mucopolysaccharidosis VII depends on the levels of beta-glucuronidase secreted by gene-corrected cells; therefore, enrichment of transduced cells expressing high levels of enzyme prior to transplantation is desirable. We describe the development of a fluorescence-activated cell sorter-based assay for the quantitative analysis of beta-glucuronidase activity in viable cells. Murine mucopolysaccharidosis VII cells transduced with a beta-glucuronidase retroviral vector can be isolated by cell sorting on the basis of beta-glucuronidase activity and cultured for further use. In vitro analysis revealed that sorted cells have elevated levels of beta-glucuronidase activity and secrete higher levels of cross-correcting enzyme than the population from which they were sorted. Transduced fibroblasts stably expressing beta-glucuronidase after subcutaneous passage in the mucopolysaccharidosis VII mouse can be isolated by cell sorting and expanded ex vivo. A relatively high percentage of these cells maintain stable expression after secondary transplantation, yielding significantly higher levels of enzymatic activity than that generated in the primary transplant.

Pairs of violet-light-excited fluorochromes for flow cytometric analysis

We describe pairs of fluorochromes for use with the 407-nm line of a violet-light-enhanced krypton ion laser. These fluorochromes and a previously described violet-light-excited reporter variant, GFP-Vex, fall into two emission classes: blue for Cascade Blue, and green/yellow for Cascade Yellow, Lucifer Yellow, and GFP-Vex. Cascade Yellow is a new fluorochrome that we have synthesized and is used for the first time in the present study. The two emission classes are sufficiently different that Cascade Blue can be paired with Cascade Yellow, Lucifer Yellow, or GFP-Vex in flow cytometric analysis. Furthermore, with proper detection filters, these fluorochromes can be combined with all of the currently used fluorochromes in a three-laser FACS system. With these data, the total number of fluorochromes that can be used as antibody labels for simultaneous detection in combined FACS analysis increases to nine. This study demonstrates the sensitivity and power of the combined use of these reagents in a single eight-color analysis by identifying murine T-lymphocyte subsets that could not otherwise be readily distinguished.

CD1 expression defines subsets of follicular and marginal zone B cells in the spleen: beta 2-microglobulin-dependent and independent forms

We have used multicolor FACS analysis, immunohistology, and functional assays to study the expression of CD1 on B cell subsets from normal and beta 2m-/- mice. Two B cell subpopulations were identified that express high levels of CD1 in normal mice: splenic marginal zone B cells (IgMhigh IgDlow CD21high CD24intermediate CD23- CD43-) and a newly identified subpopulation of follicular B cells. The latter cells are unusual, because they are IgDhigh CD23+, like follicular B cells, but express high levels of CD21 and IgM, an expression pattern that is associated with marginal zone B cells. Therefore, the high-level expression of CD1 and CD21 was found to be closely associated on splenic B cells. Immunohistology confirmed the expression of CD1 on marginal zone B cells and on clusters of B cells in splenic follicles. Both the high-level CD1 expression by these cells and the low-level CD1 expression by subpopulations of B cells in the spleen, lymph node, peritoneal cavity, and bone marrow were markedly reduced in beta 2m-/- mice. Despite this, a CD1-restricted T cell clone proliferated vigorously in response to LPS-activated spleen cells that had been obtained from both beta 2m-/- and wild-type mice. This response was inhibited by the 3C11 anti-CD1 mAb. These results show the heterogeneity of B cell subsets in their expression of the beta 2m-dependent form of CD1. They further suggest that a beta 2m-independent form of CD1 is expressed on B cells that can stimulate T cells; however, this form is not easily visualized with the anti-CD1 mAb used here.

Glutathione levels in antigen-presenting cells modulate Th1 versus Th2 response patterns

Current thinking attributes the balance between T helper 1 (Th1) and Th2 cytokine response patterns in immune responses to the nature of the antigen, the genetic composition of the host, and the cytokines involved in the early interaction between T cells and antigen-presenting cells. Here we introduce glutathione, a tripeptide that regulates intracellular redox and other aspects of cell physiology, as a key regulatory element in this process. By using three different methods to deplete glutathione from T cell receptor transgenic and conventional mice and studying in vivo and/or in vitro responses to three distinct antigens, we show that glutathione levels in antigen-presenting cells determine whether Th1 or Th2 response patterns predominate. These findings present new insights into immune response alterations in HIV and other diseases. Further, they potentially offer an explanation for the well known differences in immune responses in "Th1" and "Th2" mouse strains.

Neutrophil CD11b expression as a diagnostic marker for early-onset neonatal infection

OBJECTIVES

To determine whether neutrophil surface expression of CD11b predicts early-onset infection or suspected infection in at-risk infants.

STUDY DESIGN

CD11b expression on peripheral blood neutrophils was determined by flow cytometry of whole blood samples. Blood (0.1 ml) was obtained from a convenience sample of at-risk infants admitted to the neonatal intensive care unit, stained with antibodies detecting CD11b and CD15, chilled, and analyzed within 8 hours. Blood for culture, blood counts, and C-reactive protein (CRP) determination was obtained simultaneously. Subjects were grouped on the basis of culture results and clinical signs, and investigators were blinded to CD11b level.

RESULTS

Of 106 subjects, seven had positive bacterial or viral cultures ("confirmed infection"), 17 had clinical signs of infection but negative cultures ("suspected infection"), and 82 had negative cultures and no clinical signs ("no infection"). Neutrophil CD11b was elevated in all infants with confirmed infection, 94% with suspected infection, and none with no infection. The negative and positive predictive values, sensitivity, and specificity were 100%, 99%, 96%, and 100%, respectively, for diagnosis of neonatal infection at initial evaluation. CD11b levels correlated with peak CRP (r2 = 0.76, p < 0.0001); however, CD11b was elevated at the time of admission in all five infants with proven bacterial infection, whereas CRP was normal until the second day in the neonatal intensive care unit in three of these five. Both infants with positive viral cultures had elevated CD11b, but the CRP levels remained within normal limits. The negative predictive value of neutrophil CD11b for identifying suspected or confirmed infection was 99%.

CONCLUSION

This assay for neutrophil CD11b is a promising test for exclusion of early-onset neonatal infection. If validated prospectively, this assay may reduce hospital and antibiotic use in the population of neonates at risk for early-onset infection.

Presence of germline and full-length IgA RNA transcripts among peritoneal B-1 cells

Next to conventional B cells (or B-2 cells), peritoneal B-1 cells have been shown to contribute significantly to the production of IgA-secreting plasma cells in the gut. Evidence for this was mainly based on studies comprising manipulated animals, including lethally X-irradiated and transgenic mice. To examine the ability of peritoneal B-1 cells from untreated mice to switch actively to IgA in vivo, we performed RT-PCR analysis on FACS-sorted peritoneal B-cell subsets from untreated BALB/c mice in order to examine the presence of germline C alpha mRNA and mature C alpha mRNA transcripts. Germline C alpha and mature C alpha transcripts were readily detectable in peritoneal B-1 cells (defined as IgMbright/IgDdull), but not, or very little, in peritoneal B-2 cells (defined as IgMdull/IgDbright). Moreover, by subdividing the B-1-cell population in CD5+ B-1a cells and CD5- B-1b cells, it was shown that in vivo expression of germline C alpha and mature C alpha transcripts was largely restricted to the B-1b-cell lineage. These results indicate that peritoneal B-1 cells indeed are capable to switch to IgA under normal physiological conditions and hereby further support the view that B-1 cells contribute significantly to the mucosal IgA response, albeit this function appears to be restricted to the B-1b-cell subset.

Dynamics of fine T-cell subsets during HIV disease and after thymic ablation by mediastinal irradiation

The T-cell compartment is considerably more complex than just CD4 and CD8 T cells. Indeed, we can identify dozens of functionally and phenotypically distinct subsets within the peripheral blood of humans. These subsets are differentially affected in diseases which may underly some of the functional defects attributable to the disease. In HIV disease, all thymic-derived T-cell populations are gradually lost at identical rates during late-stage disease progression, while unusual, perhaps extrathymically-derived T cells expand. This expansion may reflect an attempt on the part of the immune system to compensate for the significant insult of HIV infection to the host: the abrogation of normal thymopoiesis and T-cell homeostasis.

Long-term depletion of naive T cells in patients treated for Hodgkin's disease

We investigated the representation of T cells in patients who had been treated for Hodgkin's disease (HD). We found a marked depletion in both CD4 and CD8 naive T-cell counts that persists up to 30 years after completion of treatment. In contrast, CD4 and CD8 memory T-cell subsets recovered to normal or above normal levels by 5 years posttreatment. Thus, the previously-reported long-term deficit in total CD4 T-cell counts after treatment for HD is due to specific depletion of naive T cells. Similarly, total CD8 T-cell counts return to normal by 5 years only because CD8 memory T cells expand to higher than normal levels. These findings suggest that the treatment (mediastinal irradiation) results in a longterm dysregulation of T-cell subset homeostasis. The profound depletion of naive T cells may explain the altered T-cell function in treated patients, including the poor response to immunization after treatment for HD. Further, in some individuals, we identified expansions of unusual subsets expressing low levels of CD8. Eight-color fluorescence-activated cell sorting analyses showed that these cells largely express CD8alphaalpha homodimers and CD57, consistent with the phenotype of potentially extrathymically derived T cells. In addition, these cells, both CD4+ and CD4-, are probably cytotoxic lymphocytes, as they express high levels of intracellular perforin. In adults treated for HD, an increased activity of extrathymic T-cell differentiation may partially compensate for the loss of thymic-derived T cells.

Interleukin-1 beta converting enzyme-like protease involvement in Fas-induced and activation-induced peripheral blood T cell apoptosis in HIV infection. TNF-related apoptosis-inducing ligand can mediate activation-induced T cell death in HIV infection

Apoptosis of peripheral blood T cells has been suggested to play an important role in the pathogenesis of human immunodeficiency virus (HIV) infection. Spontaneous, Fas (CD95)-induced and activation-induced T cell apoptosis have all been described in peripheral blood mononuclear cell cultures of HIV-infected individuals. We have previously shown that activation-induced T cell apoptosis is Fas independent in peripheral blood T cells from HIV+ individuals. In this study, we extend and confirm these observations by using an inhibitor of interleukin-1 beta converting enzyme (ICE) homologues. We show that z-VAD-fmk, a tripeptide inhibitor of ICE homologues, can inhibit Fas-induced apoptosis of peripheral blood CD4(+) and CD8+ T cells from asymptomatic HIV+ individuals. z-VAD-fmk also inhibited activation (anti-CD3)- induced CD4+ and CD8+ T cell apoptosis (AICD) in some but not all asymptomatic HIV+ individuals. Apoptosis was measured by multiparameter flow cytometry. The z-VAD-fmk inhibitor also enhanced survival of T cells in anti-Fas or anti-CD3 antibody-treated cultures and inhibited DNA fragmentation. AICD that could be inhibited by z-VAD-fmk was Fas independent and could be inhibited with a blocking monoclonal antibody to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a recently described member of the TNF/nerve growth factor ligand family. The above findings show that Fas-induced T cell apoptosis is ICE dependent in HIV infection. AICD can be blocked by ICE inhibitors in some patients, and this AICD is mediated by TRAIL. These results show that TRAIL can be a mediator of AICD in T cells. These different mechanisms of peripheral blood T cell apoptosis may play different roles in the pathogenesis of HIV infection.

HIV type 1 Tat protein enhances activation-but not Fas (CD95)-induced peripheral blood T cell apoptosis in healthy individuals

T cell apoptosis may play an important role in the depletion and functional defects of T cells in HIV disease. A number of investigators have shown that peripheral blood T cells in HIV disease undergo spontaneous and activation-induced apoptosis. We found recently that peripheral blood T cells from HIV+ individuals undergo apoptosis when stimulated through Fas. Also, a number of investigators have shown that Tat protein from HIV-1 can increase spontaneous and activation-induced apoptosis. In the present study we examined the effect of HIV type 1 Tat protein on spontaneous, activation-induced and Fas-induced apoptosis of peripheral blood T cells from HIV- individuals. We find that Tat protein has no effect on spontaneous apoptosis but does enhance activation-induced apoptosis of both CD4+ and CD8+ T cells. Tat, however, failed to enhance Fas-induced apoptosis of CD4+ and CD8+ T cells. Examining the mechanisms by which Tat induces apoptosis, we found that inhibitors of reactive oxygen intermediate (ROI) generation or neutralizers of ROI, such as rotenone, a potent inhibitor of mitochondrial complex I of the respiratory chain, and 3,3,5,5-tetramethylpyrroline N-oxide (TMPO), an electron spin trap, could both enhance the spontaneous apoptosis induced by Tat. This enhancement of Tat-induced apoptosis by rotenone and TMPO was independent of ICE activation as it could not be inhibited by the tripeptide z-VAD-fmk, an irreversible inhibitor of ICE/ced-3 protease homologs. These findings suggest that Tat induced enhancement of activation-induced cell death may involve complex mechanisms, some of which are ROI independent. These results indicate that a HIV-specific mechanism other than Tat is responsible for the previously observed increased susceptibility of peripheral blood T cells from HIV-infected individuals to undergo apoptosis in response to Fas stimulation.

Frequent occurrence of identical heavy and light chain Ig rearrangements

Single-cell PCR analyses of expressed Ig H and L chain sequences presented here show that certain rearrangements occur repeatedly and account for a major segment of the well-studied repertoire of B-1 cell autoantibodies that mediate the lysis of bromelain-treated mouse erythrocytes, i.e. antibodies reactive with phosphatldyicholine (PtC). We repeatedly isolated at least 10 different types of VH region rearrangements, involving three distinct germline genes, among FACS-sorted PtC-binding B-1 cells from three strains of mice (C57BL/6J, BALB/c and C.B-17). The predominant rearrangement, VH11-DSP-JH1 (VH11 type 1), has been previously found in anti-PtC hybridomas in several studies. We show that within each of six mice from two strains (C57BL/6J and BALB/c), unique instances of IgH/IgL pairing arose either from different B cell progenitors prior to IgH rearrangement or from pre-B cells which expanded after IgH rearrangement but prior to IgL rearrangement. Together with other recurrent rearrangements described here, our findings demonstrate that clonal expansion of mature B cells cannot account for all repeated rearrangements. As suggested by initial studies of dominant idiotype expression, these findings confirm that clonal expansion is only one of the mechanisms contributing to the establishment of recurrent rearrangements.

Detection and isolation of gene-corrected cells in Gaucher disease via a fluorescence-activated cell sorter assay for lysosomal glucocerebrosidase activity

Gaucher disease type 1 results from the accumulation of glucocerebroside in macrophages of the reticuloendothelial system, as a consequence of a deficiency in glucocerebrosidase (GC) activity. Recent improvements in the methodologies for introducing foreign genes into bone marrow stem cells have prompted several groups to test the efficacy of gene transfer therapy as a curative treatment for Gaucher disease. Limitations of this approach include the potential for insufficient engraftment of gene-corrected cells and incomplete transduction of hematopoietic stem cells using retroviral gene transfer. Overcoming these obstacles may be critical in the case of treatment for Gaucher disease type 1, because GC transduced cells have not been shown to have a growth advantage over noncorrected cells. Here, we describe the development and application of a novel, fluorescence-activated cell sorter based assay that directly quantitates GC activity at the single cell level. In a test of this application, fibroblasts from a Gaucher patient were transduced, and high expressing cells sorted based on GC activity. Reanalysis of cultured sorted fibroblasts reveals that these cells maintain high levels of enzymatic activity, compared with the heterogeneous population from which they were sorted. The assay is sufficiently sensitive to distinguish GC activity found in Gaucher patient monocytes from that in normal controls. Furthermore, preliminary results indicate that increased GC activity can be detected in transduced, CD34+ enriched peripheral blood mononuclear cells isolated from a Gaucher patient. This method should be a useful addition to current gene therapy protocols as a means to quantitatively assess gene correction of relevant cell populations and potentially purify transduced cells for transplantation.