Pregnancy-Associated Death in Utah: Contribution of Drug-Induced Deaths

OBJECTIVE

Drug-induced deaths, defined as intentional or unintentional consumption of illicit substances or diverted medications leading to death, are the leading cause of death for reproductive-age women in the United States. Our objective was to describe pregnancy-associated deaths attributed to drug-induced causes to identify opportunities for intervention.

METHODS

Using the Utah Perinatal Morality Review Committee database, we performed a retrospective cohort study of all pregnancy-associated deaths-death of a woman during pregnancy or within 1 year from the end of pregnancy-from 2005 to 2014. We performed a detailed descriptive analysis of women with drug-induced deaths. We compared characteristics of women with drug-induced and other pregnancy-associated deaths.

RESULTS

From 2005 to 2014, 136 pregnancy-associated deaths were identified. Drug-induced death was the leading cause of pregnancy-associated death (n=35, 26%) and 89% occurred in the postpartum period. More specifically, those with a drug-induced death were more likely to die in the late postpartum period, defined as death occurring within 43 days to 1 year of the end of the pregnancy, (n=28/35, 80%) compared with women whose deaths were from other pregnancy-associated causes (n=34/101, 34%) (P<.001). The majority of drug-induced deaths were attributed to opioids (n=27/35, 77%), prescription opioids (n=21/35, 60%), and polysubstance use (n=29/35, 83%). From 2005 to 2014, the pregnancy-associated mortality ratio increased 76%, from 23.3 in 2005 to 41.0 in 2014. During this same time period, the drug-induced pregnancy-associated mortality ratio increased 200%, from 3.9 in 2005 to 11.7 in 2014.

CONCLUSION

Drug-induced death is the leading cause of pregnancy-associated death in Utah and occurs primarily in the late postpartum period. Interventional studies focused on identifying and treating women at risk of drug-induced death are urgently needed.

Improved cultivation systems for isolation of the colorado potato beetle spiroplasma

In North America, the Colorado potato beetle, Leptinotarsa decemlineata, is often infected with the host-specific, gut-inhabiting Colorado potato beetle spiroplasma (CPBS). CPBS is apparently a commensal, but it may be useful in biocontrol if it can be transformed to express an insect-lethal gene. Difficulty in cultivating the organism, however, has hindered the development of a suitable transformation system. In this study, we eliminated the need for coculturing CPBS with insect cells. CPBS was reliably isolated with the BBL Anaerobic GasPak Jar system (low redox, enhanced CO(inf2)), which was easier to use and less expensive than insect cell coculture methods. A further advantage is a reduction in contaminating insect cell components. Use of anaerobiosis should facilitate early-passage screening of isolates for extrachromosomal elements, for use in gene vector constructs. The unique spiral (decreasing amplitude of coils) morphology of CPBS was preserved by anaerobiosis. The use of low-pH (6.0 to 6.5) media allowed aerobic adaptation of CPBS to M1D and SP-4 broth media. These formulations permitted the first cultivation of CPBS on solid media, an accomplishment that will simplify the selection of molecular transformants. Potato beetles collected at four sites in Poland yielded CPBS strains similar to those previously obtained from populations in North America.

Effects of oral commensal and pathogenic bacteria on human dendritic cells

BACKGROUND/AIMS

The oral cavity harbors a diverse and complex microbial community. Bacteria accumulate on both the hard and soft oral tissues in sessile biofilms and engage the host in an intricate cellular dialog, which normally constrains the bacteria to a state of commensal harmony. Dendritic cells (DCs) are likely to balance tolerance and active immunity to commensal microorganisms as part of chronic inflammatory responses. While the role played by DCs in maintaining intestinal homeostasis has been investigated extensively, relatively little is known about DC responses to oral bacteria.

METHODS

In this study, we pulsed human monocyte-derived immature DCs (iDCs) with cell wall extracts from pathogenic and commensal gram-positive or gram-negative oral bacteria.

RESULTS

Although all bacterial extracts tested induced iDCs to mature and produce cytokines/chemokines including interleukin-12p40, tumor necrosis factor-alpha, and monocyte chemoattractant protein-1 (MCP-1), the most important factor for programming DCs by oral bacteria was whether they were gram-positive or gram-negative, not whether they were commensal or pathogenic. In general, gram-negative oral bacteria, except for periodontopathic Porphyromonas gingivalis, stimulated DC maturation and cytokine production at lower concentrations than gram-positive oral bacteria. The threshold of bacteria needed to stimulate chemokine production was 100-fold to 1000-fold lower than that needed to induce cytokines. In addition, very low doses of oral commensal bacteria triggered monocytes to migrate toward DC-derived MCP-1.

CONCLUSION

Oral commensal and pathogenic bacteria do not differ qualitatively in how they program DCs. DC-derived MCP-1 induced in response to oral commensal bacteria may play a role, at least in part, in the maintenance of oral tissue integrity by attracting monocytes.

Functional genomic and serological analysis of the protective immune response resulting from vaccination of macaques with an NS1-truncated influenza virus

We are still inadequately prepared for an influenza pandemic due to the lack of a vaccine effective for subtypes to which the majority of the human population has no prior immunity and which could be produced rapidly in sufficient quantities. There is therefore an urgent need to investigate novel vaccination approaches. Using a combination of genomic and traditional tools, this study compares the protective efficacy in macaques of an intrarespiratory live influenza virus vaccine produced by truncating NS1 in the human influenza A/Texas/36/91 (H1N1) virus with that of a conventional vaccine based on formalin-killed whole virus. After homologous challenge, animals in the live-vaccine group had greatly reduced viral replication and pathology in lungs and reduced upper respiratory inflammation. They also had lesser induction of innate immune pathways in lungs and of interferon-sensitive genes in bronchial epithelium. This postchallenge response contrasted with that shortly after vaccination, when more expression of interferon-sensitive genes was observed in bronchial cells from the live-vaccine group. This suggested induction of a strong innate immune response shortly after vaccination with the NS1-truncated virus, followed by greater maturity of the postchallenge immune response, as demonstrated with robust influenza virus-specific CD4+ T-cell proliferation, immunoglobulin G production, and transcriptional induction of T- and B-cell pathways in lung tissue. In conclusion, a single respiratory tract inoculation with an NS1-truncated influenza virus was effective in protecting nonhuman primates from homologous challenge. This protection was achieved in the absence of significant or long-lasting adverse effects and through induction of a robust adaptive immune response.

How does B cell depletion therapy work, and how can it be improved?

The past few years have seen a surge of interest in B cell depletion therapy for patients with rheumatoid arthritis. This paper outlines the possible mechanism(s) by which B cell depletion therapy works. It is likely there is more than one mechanism and the relative importance of each mechanism depends on the target cell. These include CD20-induced apoptosis, complement dependent cytotoxicity, antibody dependent cell-mediated cytotoxicity, and selective targeting and depletion of B cell subsets. The implications of these mechanisms in the further improvement of B cell depletion therapy in rheumatoid arthritis and other autoimmune diseases are discussed.

Differential expression of CD180 and IgM by B-cell chronic lymphocytic leukaemia cells using mutated and unmutated immunoglobulin VH genes

We have studied the surface expression of the Toll-like receptor family member CD 180 on cells from 78 patients with B-chronic lymphocytic leukaemia (B-CLL). B-CLL cells had variable levels of CD 180 expression, but this was always less than that expressed by normal blood B cells and was stable for 24 months. Significantly higher levels of CD 180 were expressed by B-CLL cells with mutated IGVH genes compared with those using unmutated IGVH genes. This was in contrast to the higher levels of expression of surface immunoglobulin M by B-CLL cells using unmutated, rather than mutated IGVH genes. CD 180 was functional on B-CLL cells from some of the patients, as shown by the increased expression of CD 86 following incubation in vitro with anti-CD 180. The differential expression of CD 180 amongst B-CLL patients is one more marker that may define more precisely the different biological properties of this heterogeneous disease.

Tumor necrosis factor-alpha regulates the expression of inducible costimulator receptor ligand on CD34(+) progenitor cells during differentiation into antigen presenting cells

The inducible costimulator receptor (ICOS) is a third member of the CD28 receptor family that regulates T cell activation and function. ICOS binds to a newly identified ligand on antigen presenting cells different from the CD152 ligands CD80 and CD86. We used soluble ICOSIg and a newly developed murine anti-human ICOS ligand (ICOSL) monoclonal antibody to further characterize the ICOSL during ontogeny of antigen presenting cells. In a previous study, we found that ICOSL is expressed on monocytes, dendritic cells, and B cells. To define when ICOSL is first expressed on myeloid antigen presenting cells, we examined ICOSL expression on CD34(+) cells in bone marrow. We found that CD34(bright) cells regardless of their myeloid commitment were ICOSL(-), whereas ICOSL was first expressed when CD34 expression diminished and the myeloid marker CD33 appeared. However, acute myeloid leukemia cells were ICOSL-negative, whereas among B-cell malignancies only some cases of the most mature tumors such as prolymphocytic leukemia and hairy cell leukemia were positive. Next, we investigated purified CD34(+) hematopoietic progenitor cells that did not constitutively express ICOSL but were induced to express ICOSL within 12 h after granulocyte/macrophage colony-stimulating factor/tumor necrosis factor alpha (TNF-alpha) stimulation. Interestingly, ICOSL was induced prior to CD80/CD86 induction on CD34(+) cells so that ICOSL was expressed in the absence of CD80/CD86. This suggests that ICOSL is an early differentiation marker along the monocytic/dendritic maturation pathway. Induction of ICOSL was dependent on TNF-alpha and was regulated via NF-kappa B as revealed by use of inhibitors specific for I kappa B alpha phosphorylation such as BAY 11-7082 and BAY 11-7085. The antigen presenting capacity of TNF-alpha stimulated CD34(+) cells was strongly inhibited by ICOSIg fusion proteins or by NF-kappa B inhibition. Thus, TNF-alpha-induced ICOSL expression seemed to be functionally important for the costimulatory capacity of CD34(+) hematopoietic progenitor cells.

CD22 regulates B cell receptor-mediated signals via two domains that independently recruit Grb2 and SHP-1

Recognition of antigen by the B cell antigen receptor (BCR) determines the subsequent fate of a B cell and is regulated in part by the involvement of other surface molecules, termed coreceptors. CD22 is a B cell-restricted coreceptor that gets rapidly tyrosyl-phosphorylated and recruits various signaling molecules to the membrane following BCR ligation. Although CD22 contains three immunoreceptor tyrosine-based inhibitory motifs (ITIMs), only the two carboxyl-terminal ITIM tyrosines are required for efficient recruitment of the SHP-1 phosphatase after BCR ligation. Furthermore, Grb2 is inducibly recruited to CD22 in human and murine B cells. Unlike SHP-1, Grb2 recruitment to CD22 is not inhibited by specific doses of the Src family kinase-specific inhibitor PP1. The tyrosine residue in CD22 required for Grb2 recruitment (Tyr-828) is distinct and independent from the two ITIM tyrosines required for efficient SHP-1 recruitment (Tyr-843 and Tyr-863). Individually both Lyn and Syk are required for maximal phosphorylation of CD22 following ligation of the BCR, and together Lyn and Syk are required for all of the constitutive and induced tyrosine phosphorylation of CD22. We propose that the cytoplasmic tail of CD22 contains two domains that regulate signal transduction pathways initiated by the BCR and B cell fate.

In vitro susceptibility of Stenotrophomonas maltophilia to various antimicrobial combinations

Stenotrophomonas maltophilia has emerged as a significant pathogen in compromised patients, causing infections which are difficult to treat. Clinical isolates from patients in the Tucson area were tested against single and combination antibiotics using three testing methods. Ticarcillin/clavulanate, trimethoprim/sulfamethoxazole and trovafloxacin provided comparable inhibitory activity, in vitro. Ciprofloxacin, imipenem and ticarcillin were active less often. Agreements between disk diffusion and broth microdilution results were poor for ciprofloxacin and trimethoprim/sulfamethoxazole; however, agreement was > or = 90% for the other drugs tested. Major or very major errors were observed with ticarcillin, ticarcillin/clavulanate, and trovafloxacin. The addition of aztreonam to ticarcillin/clavulanate enhanced the activity compared to ticarcillin/clavulanate alone using the double-disk diffusion, broth microdilution (checkerboard), and time-kill testing methods. Trovafloxacin exhibited good activity by all three methods, with bactericidal activity at > or = 2x MIC. These results indicate that the newer fluoroquinolones or the triple combination of ticarcillin/clavulanate plus aztreonam may be potential options for treatment of infection caused by S. maltophilia in patients who are intolerant to or fail trimethoprim/sulfamethoxazole therapy.

B cells with the guts to switch

Expression of mIgM was thought to be esential for the differentiation of B cells expressing antibodies of other classes. New evidence suggests isotype class switching to IgA can occur in the absence of mIgM.

High-throughput multi-analyte screening for renal disease using capillary electrophoresis

End-state renal disease (ESRD) affects 300000 people in the United States each year. A large percentage of these individuals (approximately 20%) die within the first year after diagnosis. Current methods of determining renal function rely on the measurement of a single marker using slow and frequently non-specific colorimetric methods. In this report, capillary zone electrophoresis was used to perform a multi-analyte assay for markers of renal function in urine. This method tested for creatinine (Cr), creatine (Cn), uric acid (UA), and p-aminohippuric acid (PAH) levels. The limits of detection (S/N=3) were found to be 5 microM for Cr, 0.75 microM for Cn, and 1.5 microM for UA and PAH. Linear ranges were determined to be 5-500 microM for Cr, 0.75-500 microM for Cn, and 1.5-250 microM for UA and PAH. These ranges included the expected concentrations of the markers in human urine after 50-fold dilution. This screening method proved to be a simple and fast way to perform a high throughput analysis for multiple renal function indicators.

CD95/Fas induces cleavage of the GrpL/Gads adaptor and desensitization of antigen receptor signaling

The balance between cell survival and cell death is critical for normal lymphoid development. This balance is maintained by signals through lymphocyte antigen receptors and death receptors such as CD95/Fas. In some cells, ligating the B cell antigen receptor can protect the cell from apoptosis induced by CD95. Here we report that ligation of CD95 inhibits antigen receptor-mediated signaling. Pretreating CD40-stimulated tonsillar B cells with anti-CD95 abolished B cell antigen receptor-mediated calcium mobilization. Furthermore, CD95 ligation led to the caspase-dependent inhibition of antigen receptor-induced calcium mobilization and to the activation of mitogen-activated protein kinase pathways in B and T cell lines. A target of CD95-mediated caspase 3-like activity early in the apoptotic process is the adaptor protein GrpL/Gads. GrpL constitutively interacts with SLP-76 via its C-terminal SH3 domain to regulate transcription factors such as NF-AT. Cleavage of GrpL removes the C-terminal SH3 domain so that it is no longer capable of recruiting SLP-76 to the membrane. Transfection of a truncated form of GrpL into Jurkat T cells blocked T cell antigen receptor-induced activation of NF-AT. These results suggest that CD95 signaling can desensitize antigen receptors, in part via cleavage of the GrpL adaptor.

Involvement of Bik, a proapoptotic member of the Bcl-2 family, in surface IgM-mediated B cell apoptosis

Apoptosis plays a central role in shaping the repertoire of circulating mature B lymphocytes, but the underlying molecular mechanisms regulating B cell fate are not well understood. Human B104 B lymphoma cells undergo apoptosis after surface Ig (sIg)M, but not sIgD, ligation; sIgM-mediated apoptosis of B104 cells apparently requires new gene transcription because actinomycin D can inhibit the apoptotic response. Here we report that expression of Bik, a proapoptotic member of the Bcl-2 family, is greatly increased after sIgM ligation. Bik expression was tightly controlled at both transcriptional and post-transcriptional levels. Whereas a calcineurin-dependent pathway was essential for Bik mRNA induction, both the phosphatidylinositol 3-kinase (PI3K)- and the calcineurin-dependent pathways were required for the sustained production of Bik protein. Consistent with these findings, sIgD ligation, which leads to the similar calcium mobilization and increases in Bik mRNA, induced only a transient activation of PI3K and did not lead to sustained Bik protein expression. Furthermore, sustained Bik protein expression correlated with B cell apoptosis, as treatment with either a calcineurin inhibitor or PI3K inhibitors blocked both sIgM-mediated sustained Bik protein induction and apoptosis. In addition, sIgM ligation strongly increased the amount of Bik associated with endogenous Bcl-x, but sIgD ligation did not. Studies with caspase inhibitors also revealed that Bik and Bcl-x interacted upstream of caspases in the B cell apoptosis cascade. Thus, Bik protein induction and, subsequently, sequestering of antiapoptotic Bcl-x by Bik may play an important role in regulating B cell apoptosis.

Both phosphorylation and caspase-mediated cleavage contribute to regulation of the Ste20-like protein kinase Mst1 during CD95/Fas-induced apoptosis

The serine/threonine kinase Mst1, a mammalian homolog of the budding yeast Ste20 kinase, is cleaved by caspase-mediated proteolysis in response to apoptotic stimuli such as ligation of CD95/Fas or treatment with staurosporine. Furthermore, overexpression of Mst1 induces morphological changes characteristic of apoptosis in human B lymphoma cells. Mst1 may therefore represent an important target for caspases during cell death which serves to amplify the apoptotic response. Here we report that Mst1 has two caspase cleavage sites, and we present evidence indicating that cleavage may occur in an ordered fashion and be mediated by distinct caspases. We also show that caspase-mediated cleavage alone is insufficient to activate Mst1, suggesting that full activation of Mst1 during apoptosis requires both phosphorylation and proteolysis. Another role of phosphorylation may be to influence the susceptibility of Mst1 to proteolysis. Autophosphorylation of Mst1 on a serine residue close to one of the caspase sites inhibited caspase-mediated cleavage in vitro. Finally, Mst1 appears to function upstream of the protein kinase MEKK1 in the SAPK pathway. In conclusion, Mst1 activity is regulated by both phosphorylation and proteolysis, suggesting that protein kinase and caspase pathways work in concert to regulate cell death.

CD150 association with either the SH2-containing inositol phosphatase or the SH2-containing protein tyrosine phosphatase is regulated by the adaptor protein SH2D1A

CD150 (SLAM/IPO-3) is a cell surface receptor that, like the B cell receptor, CD40, and CD95, can transmit positive or negative signals. CD150 can associate with the SH2-containing inositol phosphatase (SHIP), the SH2-containing protein tyrosine phosphatase (SHP-2), and the adaptor protein SH2 domain protein 1A (SH2D1A/DSHP/SAP, also called Duncan's disease SH2-protein (DSHP) or SLAM-associated protein (SAP)). Mutations in SH2D1A are found in X-linked lymphoproliferative syndrome and non-Hodgkin's lymphomas. Here we report that SH2D1A is expressed in tonsillar B cells and in some B lymphoblastoid cell lines, where CD150 coprecipitates with SH2D1A and SHIP. However, in SH2D1A-negative B cell lines, including B cell lines from X-linked lymphoproliferative syndrome patients, CD150 associates only with SHP-2. SH2D1A protein levels are up-regulated by CD40 cross-linking and down-regulated by B cell receptor ligation. Using GST-fusion proteins with single replacements of tyrosine at Y269F, Y281F, Y307F, or Y327F in the CD150 cytoplasmic tail, we found that the same phosphorylated Y281 and Y327 are essential for both SHP-2 and SHIP binding. The presence of SH2D1A facilitates binding of SHIP to CD150. Apparently, SH2D1A may function as a regulator of alternative interactions of CD150 with SHP-2 or SHIP via a novel TxYxxV/I motif (immunoreceptor tyrosine-based switch motif (ITSM)). Multiple sequence alignments revealed the presence of this TxYxxV/I motif not only in CD2 subfamily members but also in the cytoplasmic domains of the members of the SHP-2 substrate 1, sialic acid-binding Ig-like lectin, carcinoembryonic Ag, and leukocyte-inhibitory receptor families.

Osteoprotegerin, a crucial regulator of bone metabolism, also regulates B cell development and function

Osteoprotegerin (OPG) is a CD40-regulated gene in B cells and dendritic cells (DCs). We investigated the role of OPG in the immune system by generating opg(-/-) mice. Like its role as a regulator of bone metabolism, OPG also influences processes in the immune system, notably in B cell development. Ex vivo, opg(-/-) pro-B cells have enhanced proliferation to IL-7, and in opg(-/-) spleen, there is an accumulation of type 1 transitional B cells. Furthermore, opg(-/-) bone marrow-derived DCs are more effective in stimulating allogeneic T cells than control DCs. When challenged with a T-dependent Ag, opg(-/-) mice had a compromised ability to sustain an IgG3 Ag-specific response. Thus, in the immune system, OPG regulates B cell maturation and development of efficient Ab responses.

Infection of CD4+ memory T cells by HIV-1 requires expression of phosphodiesterase 4

Using PCR to monitor HIV-1 RNA genome reverse transcription and nuclear import of preintegration complexes, we found that memory, but not naive, CD4+ T cells could support transport of HIV-1 DNA to nuclei upon TCR/CD3 and IL-2 stimulation. Moreover, memory CD4+ T cells, unlike naive CD4+ T cells, express high levels of phosphodiesterase 4 (PDE4) constitutively. Selective blocking of PDE4 activity inhibited IL-2R expression and thereby led to abolishing HIV-1 DNA nuclear import in memory T cells; however, full-length viral DNA synthesis was not affected. Thus, blocking PDE4 prevents initiation of HIV-1 DNA circle formation in T cells. The fact that PDE4 is expressed constitutively at higher levels in memory vs naive CD4+ T cells may help HIV-1 readily infect memory T cells.

Genomic analysis of metastasis reveals an essential role for RhoC

The most damaging change during cancer progression is the switch from a locally growing tumour to a metastatic killer. This switch is believed to involve numerous alterations that allow tumour cells to complete the complex series of events needed for metastasis. Relatively few genes have been implicated in these events. Here we use an in vivo selection scheme to select highly metastatic melanoma cells. By analysing these cells on DNA arrays, we define a pattern of gene expression that correlates with progression to a metastatic phenotype. In particular, we show enhanced expression of several genes involved in extracellular matrix assembly and of a second set of genes that regulate, either directly or indirectly, the actin-based cytoskeleton. One of these, the small GTPase RhoC, enhances metastasis when overexpressed, whereas a dominant-negative Rho inhibits metastasis. Analysis of the phenotype of cells expressing dominant-negative Rho or RhoC indicates that RhoC is important in tumour cell invasion. The genomic approach allows us to identify families of genes involved in a process, not just single genes, and can indicate which molecular and cellular events might be important in complex biological processes such as metastasis.

Regulation of B-cell activation and differentiation by the phosphatidylinositol 3-kinase and phospholipase Cgamma pathway

Signal transduction through the B-cell antigen receptor (BCR) determines the fate of B lymphocytes during their development and during immune responses. A multitude of signal transduction events are known to be activated by ligation of the BCR; however, the critical parameters determining the biological outcome of the signal transduction cascade are only just beginning to be understood. Two enzymes which act on plasma membrane phospholipids, phosphatidylinositol 3-kinase (PI3K) and phospholipase Cgamma (PLCgamma), have been implicated as critical mediators of B-cell activation and differentiation signals. Activation of these ubiquitous enzymes is regulated by B-lymphocyte-specific signal transduction proteins, such as CD 19 and B-cell linker protein. These enzymes function by generating both membrane-anchored and soluble second messenger molecules which regulate the activity of downstream signal transduction proteins. Active PI3K produces phosphatidylinositol-3,4-bisphosphate (PI(3,4)P2) and phosphatidylinositol-3,4-trisphosphate (PI(3,4,5)P3) which can bind to signaling proteins such as Btk or Akt via their pleckstrin homology domains, resulting in their membrane recruitment and activation. The lipid phosphatases SHIP and PTEN negatively regulate production of PI(3,4)P2 and PI(3,4,S)P3 and therefore function to put a "brake" on the PI3K pathway. Active PLCgamma produces inositol-1,4,5-trisphosphate, which regulates Ca2+ mobilization, and diacylglycerol, which binds to a subset of protein kinase C enzymes leading to their membrane localization and activation. Recent evidence has indicated that PLCgamma activation is partially dependent on the PI(3,4,5)P3 production by activated PI3K. Since PI3K and PLCgamma also share common downstream targets such as the NF-AT and NF-kappaB transcription factors, it is becoming clear that these two pathways are interconnected at several levels. Studies of mice deficient in components of the PI3K and PLCgamma pathways demonstrate that these pathways play critical roles in both pre-BCR and BCR-dependent selection events during B-cell differentiation. Taken together, the present data clearly indicate that PI3K and PLCgamma play critical and indispensable roles in the signal transduction cascades leading to multiple biological responses downstream of the BCR.

Osteoprotegerin is an alpha vbeta 3-induced, NF-kappa B-dependent survival factor for endothelial cells

Osteopontin protects endothelial cells from apoptosis induced by growth factor withdrawal. This interaction is mediated by the alpha(v)beta(3) integrin and is NF-kappaB-dependent (Scatena, M., Almeida, M., Chaisson, M. L., Fausto, N., Nicosia, R. F., and Giachelli, C. M. (1998) J. Cell Biol. 141, 1083-1093). In the present study we used differential cloning to identify osteopontin-induced, NF-kappaB-dependent genes in endothelial cells. One of the genes identified in this screen was osteoprotegerin, a member of the tumor necrosis factor receptor superfamily. By Northern and Western blot analysis, osteoprotegerin mRNA and protein levels were very low in endothelial cells plated on the non-integrin cell attachment factor, poly-d-lysine. In contrast, osteoprotegerin mRNA and protein levels were induced 5-7-fold following alpha(v)beta(3) ligation by osteopontin. Osteoprotegerin induction by osteopontin was time-dependent and observed as early as 3 h following treatment. NF-kappaB inactivation achieved by over expression of an IkappaB super repressor in endothelial cells completely inhibited osteoprotegerin induction by osteopontin. Finally, purified osteoprotegerin protected endothelial cells with inactive NF-kappaB from apoptosis induced by growth factor deprivation. These data suggest that alpha(v)beta(3)-mediated endothelial survival depends on osteoprotegerin induction by NF-kappaB and indicate a new function for osteoprotegerin in endothelial cells.

Characterization of human inducible costimulator ligand expression and function

The inducible costimulator (ICOS) is the newest member of the CD28/CD152 receptor family involved in regulating T cell activation. We constructed a soluble-Ig fusion protein of the extracellular domain of human ICOS and used it as a probe to characterize expression patterns of the ICOS ligand (ICOSL). ICOSIg did not bind to CD80- or CD86-transfected Chinese hamster ovary cell lines, demonstrating that ICOSL is distinct from those ligands identified for CD28/CD152. ICOSIg showed selective binding to monocytic and B cell lines, whereas binding was undetectable on unstimulated monocytes and peripheral blood T and B cells. Expression of ICOSL was induced on monocytes after integrin-dependent plastic adhesion. Pretreatment of monocytes with mAb to the beta2-integrin subunit CD18 decreased adhesion and abolished ICOSL up-regulation but had no effect on CD80/86 (CD152 ligand (CD152L)) expression. Both ICOSL and CD152L were up-regulated on monocytes by IFN-gamma but by distinct signaling pathways. Unlike CD152L expression, ICOSL expression did not change when monocytes were differentiated into dendritic cells (DCs) or after DCs were induced to mature by LPS, TNF-alpha, or CD40 ligation. Addition of ICOSIg to allogeneic MLRs between DCs and T cells reduced T cell proliferative responses but did so less efficiently than CTLA4Ig (CD152Ig) did. Similarly, ICOSIg also blocked Ag-specific T cell proliferation to tetanus toxoid. Thus, ICOSL, like CD80/86, is expressed on activated monocytes and dendritic cells but is regulated differently and delivers distinct signals to T cells that can be specifically inhibited by ICOSIg.

A novel B lymphocyte-associated adaptor protein, Bam32, regulates antigen receptor signaling downstream of phosphatidylinositol 3-kinase

We have identified and characterized a novel src homology 2 (SH2) and pleckstrin homology (PH) domain-containing adaptor protein, designated Bam32 (for B cell adaptor molecule of 32 kD). cDNAs encoding the human and mouse Bam32 coding sequences were isolated and the human bam32 gene was mapped to chromosome 4q25-q27. Bam32 is expressed by B lymphocytes, but not T lymphocytes or nonhematopoietic cells. Human germinal center B cells show increased Bam32 expression, and resting B cells rapidly upregulate expression of Bam32 after ligation of CD40, but not immunoglobulin M. Bam32 is tyrosine-phosphorylated upon B cell antigen receptor (BCR) ligation or pervanadate stimulation and associates with phospholipase Cgamma2. After BCR ligation, Bam32 is recruited to the plasma membrane through its PH domain. Membrane recruitment requires phosphatidylinositol 3-kinase (PI3K) activity and an intact PI(3,4, 5)P(3)-binding motif, suggesting that membrane association occurs through binding to 3-phosphoinositides. Expression of Bam32 in B cells leads to a dose-dependent inhibition of BCR-induced activation of nuclear factor of activated T cells (NF-AT), which is blocked by deletion of the PH domain or mutation of the PI(3,4,5)P(3)-binding motif. Thus, Bam32 represents a novel B cell-associated adaptor that regulates BCR signaling downstream of PI3K.

Rapid shift from virally infected cells to germinal center-retained virus after HIV-2 infection of macaques

Lymphoid tissues are the primary target during the initial virus dissemination that occurs in HIV-1-infected individuals. Recent advances in antiretroviral therapy and techniques to monitor virus load in humans have demonstrated that the early stages of viral infection and host response are major determinants of the outcome of individual infections. Relatively little is known about immunopathogenic events occurring during the acute phase of HIV infection. We analyzed viral dissemination within lymphoid tissues by in situ hybridization and by combined immunohistochemistry/in situ hybridization during the acute infection phase (12 hours to 28 days) in pig-tailed macaques (Macaca nemestrina), challenged intravenously with a virulent strain of HIV-2, HIV-2(287). Two stages in viral dissemination were clearly evident within the first 28 days after HIV-2(287) infection. First, a massive increase in individual HIV-2-infected cells, mostly CD3+ T lymphocytes and a smaller percentage of macrophages and interdigitating dendritic cells, was identified within lymph nodes which peaked on the 10th day after HIV-2 infection. A shift of HIV-2 distribution was demonstrable between day 10 and day 14 after HIV-2 infection. Coincident with a marked reduction in individual HIV-2 RNA+ cells by day 14 postinfection, there was a dramatic increase in germinal center-associated HIV-2 RNA. High concentrations of HIV-2 RNA persisted in germinal centers in all animals by days 21 and 28 postinfection. Thus, HIV-2 appears to go through an initial, highly disseminated cellular phase followed by localization in the follicular dendritic cell network with relatively few infected cells. In this nonhuman primate model of HIV-associated immunopathogenesis, using a virus derived from a human pathogen, we identified a significant shift in the pattern of HIV-2 localization within a narrow time frame (day 10 to day 14). This shift in virus localization and behavior indicates that there may be a discrete but remarkably narrow window for therapeutic interventions that interrupt this stage in the natural course of HIV infection. Reproducibility and the accelerated time course of disease development make this model an excellent candidate for such intervention studies.

The CD40-inducible Bcl-2 family member A1 protects B cells from antigen receptor-mediated apoptosis

CD40 activation is necessary for thymus-dependent humoral immune responses and rescuing both phenotypically immature WEHI-231 B lymphoma cells from B cell antigen receptor-induced cell death and germinal center B cells from spontaneous apoptosis. As some effects of CD40 are probably mediated by differences in gene expression, cDNA expression arrays and RNase protection assays were used to identify the anti-apoptotic Bcl-2 homolog A1 as a CD40-inducible gene in B cell lines and purified germinal center B cells. Sustained CD40-induced A1 upregulation correlated with CD40-mediated rescue of WEHI-231 cells from anti-IgM-induced apoptosis. Moreover, overexpression of A1 specifically protected WEHI-231 cells from anti-IgM-induced apoptosis but not cell death triggered by certain other stimuli.

Signaling through the B cell antigen receptor in developing B cells

Signaling events arising from the B cell antigen receptor (BCR) complex are critical for the normal progression of a B cell through its stages of maturation. These stages are characterized by the generation and expression of BCR components. Initially, the heavy chain is formed and expressed along with the surrogate light chain and VpreB. This pre-BCR may initiate events that induce the cell to generate the light chain molecules. Proper expression of these molecules triggers the cell to develop into a mature B cell. If a key signal is absent at any stage of B cell development, maturation ceases, and either the defects are corrected or the cell undergoes apoptosis. A deficiency in the expression of several intracellular proteins required for these signaling events leads to the arrest of B cell development. Advancement to specific stages of maturation relies on a particular intensity of signal through pathways leading to the activation of a set of transcription factors. These pathways include the calcium and MAPK family pathways. Factors such as the concentration and avidity of the antigen, the coligation of co-receptors, and the formation of signaling complexes dictate the intensity of these signals and thereby the fate of the B cell at each stage of development.

Differential role for p38 mitogen-activated protein kinase in regulating CD40-induced gene expression in dendritic cells and B cells

We investigated whether human monocyte-derived dendritic cells (DCs) differed from tonsillar B cells in the set of cell fate genes they express constitutively and in the way these genes are affected after CD40 ligation. In particular, Bcl-2, TNF receptor-associated factor-2 (TRAF2), and TRAF4 were clearly inducible via CD40 in B cells but not in DCs. DCs, unlike B cells, were induced to increase expression of IL-1beta, IL-1Ra, IL-8, IL-12 p40, RANTES, macrophage inflammatory protein-1alpha, and monocyte chemoattractant protein-1 after CD40 ligation. We next tested whether CD40-induced signaling pathways were different in DCs vs B cells. In DCs, as in B cells, CD40 ligation activated p38 mitogen-activated protein kinase (MAPK), its downstream target, MAPKAPK-2, and the c-Jun N-terminal kinase. The p38 MAPK-specific inhibitor, SB203580, blocked CD40-induced MAPKAPK-2 activation, but did not affect activation of c-Jun N-terminal kinase. Furthermore, unlike in B cells, extracellular signal-regulated kinase-1 and -2 were activated after CD40 ligation in DCs. SB203580 strongly blocked CD40-induced IL-12 p40 production in DCs at both mRNA and protein levels, while having minimal effect on CD40-induced expression of the chemokine RANTES. In contrast, no detectable IL-12 p40 protein was secreted in CD40-stimulated B cells. Furthermore, CD40-induced mRNA expression of cellular inhibitor of apoptosis protein-2 was also dependent on the p38 MAPK pathway in DCs and differed compared with that in B cells. In conclusion, CD40 induces distinct programs in DCs and B cells, and the set of p38 MAPK-dependent genes in DCs (IL-12 p40 and cellular inhibitor of apoptosis protein-2) is different from that in B cells (IL-10 and IL-1beta).

Syk and Bruton's tyrosine kinase are required for B cell antigen receptor-mediated activation of the kinase Akt

Activation of Akt by multiple stimuli including B cell antigen receptor (BCR) engagement requires phosphatidylinositol 3-kinase and regulates processes including cell survival, proliferation, and metabolism. BCR cross-linking activates three families of non-receptor protein tyrosine kinases (PTKs) and these are transducers of signaling events including phospholipase C and mitogen-activated protein kinase activation; however, the relative roles of PTKs in BCR-mediated Akt activation are unknown. We examined Akt activation in Lyn-, Syk- and Btk-deficient DT40 cells and B cells from Lyn(-/-) mice. BCR-mediated Akt activation required Syk and was partially dependent upon Btk. Increased BCR-induced Akt phosphorylation was observed in Lyn-deficient DT40 cells and Lyn(-/-) mice compared with wild-type cells suggesting that Lyn may negatively regulate Akt function. BCR-induced tyrosine phosphorylation of the phosphatidylinositol 3-kinase catalytic subunit was abolished in Syk-deficient cells consistent with a receptor-proximal role for Syk in BCR-mediated phosphatidylinositol 3-kinase activation; in contrast, it was maintained in Btk-deficient cells, suggesting Btk functions downstream of phosphatidylinositol 3-kinase. Calcium depletion did not influence BCR-induced Akt phosphorylation/activation, showing that neither Syk nor Btk mediates its effects via changes in calcium levels. Thus, BCR-mediated Akt stimulation is regulated by multiple non-receptor PTK families which regulate Akt both proximal and distal to phosphatidylinositol 3-kinase activation.

A novel Epstein-Barr virus-like virus, HV(MNE), in a Macaca nemestrina with mycosis fungoides

Epstein-Barr virus (EBV) infection of humans has been associated with the development of lymphoid malignancies mainly of B-cell lineage, although occasionally T-cell lymphomas have been reported. We describe here the characterization of a novel EBV-like virus (HV(MNE)) isolated from a simian T-cell lymphotropic virus type I/II (STLV-I/II) seronegative pigtailed macaque (Macaca nemestrina) with a cutaneous T-cell lymphoma. Immunohistochemistry studies on the skin lesions demonstrated that the infiltrating cells were of the CD3(+)/CD8(+) phenotype. Two primary transformed CD8(+) T-cell lines were obtained from cultures of peripheral blood mononuclear cells (PBMC) and skin, and, with time, both cell lines became interleukin-2-independent and acquired the constitutive activation of STAT proteins. Polymerase chain reaction analysis of the DNA from the cell lines and tissues from the lymphomatous animal demonstrated the presence of a 536-bp DNA fragment that was 90% identical to EBV polymerase gene sequences, whereas the same DNA was consistently negative for STLV-I/II sequences. Electron microscopy performed on both cell lines, after sodium butyrate treatment, showed the presence of a herpes-like virus that was designated HV(MNE) according to the existing nomenclature. In situ hybridization studies using EBV Epstein-Barr viral-encoded RNA probes showed viral RNA expression in both CD8(+) T-cell lines as well as in the infiltrating CD8(+) T cells of skin-tissue biopsies. Phylogenetic analysis of a 465-bp fragment from the polymerase gene of HV(MNE) placed this virus within the Lymphocryptovirus genus and demonstrated that HV(MNE) is a distinct virus, clearly related to human EBV and other EBV-like herpesviruses found in nonhuman primates.

Isolation and characterization of macaque dendritic cells from CD34(+) bone marrow progenitors

We have developed a method for isolating and characterizing pigtailed macaque dendritic cells (DCs) generated from CD34(+) bone marrow (BM) progenitors based on methods previously developed for isolating human DCs. Macaque DCs displayed a characteristic morphology and were potent stimulators of allogeneic T cell proliferation. They expressed a set of DC-associated markers, such as MHC class II, CD1a, CD4, CD11a, CD40, CD58, CD80, CD83, CD86, and CXCR4. Macaque DCs, as well as peripheral blood CD4(+) T cells, were highly susceptible to HIV-2 infection, as detected by DNA-PCR. The expression of HIV-2 in macaque DCs was downregulated by treatment with the beta-chemokine RANTES. Macaque DCs will be useful for defining the in vivo role of DCs in HIV pathogenesis and for optimizing and testing peptide-DC vaccines or tolerizing regimens.

CDw150 associates with src-homology 2-containing inositol phosphatase and modulates CD95-mediated apoptosis

CDw150, a receptor up-regulated on activated T or B lymphocytes, has a key role in regulating B cell proliferation. Patients with X-linked lymphoproliferative disease have mutations in a gene encoding a protein, DSHP/SAP, which interacts with CDw150 and is expressed in B cells. Here we show that CDw150 on B cells associates with two tyrosine-phosphorylated proteins, 59 kDa and 145 kDa in size. The 59-kDa protein was identified as the Src-family kinase Fgr. The 145-kDa protein is the inositol polyphosphate 5'-phosphatase, SH2-containing inositol phosphatase (SHIP). Both Fgr and SHIP interact with phosphorylated tyrosines in CDw150's cytoplasmic tail. Ligation of CDw150 induces the rapid dephosphorylation of both SHIP and CDw150 as well as the association of Lyn and Fgr with SHIP. CD95/Fas-mediated apoptosis is enhanced by signaling via CDw150, and CDw150 ligation can override CD40-induced rescue of CD95-mediated cell death. The ability of CDw150 to regulate cell death does not correlate with serine phosphorylation of the Akt kinase, but does correlate with SHIP tyrosine dephosphorylation. Thus, the CDw150 receptor may function to regulate the fate of activated B cells via SHIP as well as via the DSHP/SAP protein defective in X-linked lymphoproliferative disease patients.

Expression of the c-myc proto-oncogene is essential for HIV-1 infection in activated T cells

We previously found that activation of primary CD4+ T cells via both the T cell antigen receptor (TCR) and CD28 is required for HIV-1 DNA to be translocated from the cytoplasm to the nucleus. Here we report that expression of c-Myc protein in CD4+ T cells is induced only after such costimulation. In addition, cyclosporin A not only inhibits nuclear import of HIV-1 DNA but also inhibits expression of c-Myc protein. Because of these correlations, we tested whether c-Myc is necessary for nuclear import of HIV-1 DNA. Specific c-myc antisense, but not sense or non-sense, phosphorothioate oligodeoxynucleotides selectively induced the accumulation of two NH2-terminally truncated c-Myc proteins and abolished HIV-1 genome entry into host nuclei. Consequently, both virus replication and HIV-1-induced apoptotic cell death were inhibited. Synthesis of viral full-length DNA was not affected. Specific c-myc antisense oligonucleotide inhibited HIV-1 infection under conditions that did not affect cell cycle entry or proliferation. Thus, c-Myc appears to regulate HIV-1 DNA nuclear import via a mechanism distinct from those controlling entry into the cell cycle.

GrpL, a Grb2-related adaptor protein, interacts with SLP-76 to regulate nuclear factor of activated T cell activation

Propagation of signals from the T cell antigen receptor (TCR) involves a number of adaptor molecules. SH2 domain-containing protein 76 (SLP-76) interacts with the guanine nucleotide exchange factor Vav to activate the nuclear factor of activated cells (NF-AT), and its expression is required for normal T cell development. We report the cloning and characterization of a novel Grb2-like adaptor molecule designated as Grb2-related protein of the lymphoid system (GrpL). Expression of GrpL is restricted to hematopoietic tissues, and it is distinguished from Grb2 by having a proline-rich region. GrpL can be coimmunoprecipitated with SLP-76 but not with Sos1 or Sos2 from Jurkat cell lysates. In contrast, Grb2 can be coimmunoprecipitated with Sos1 and Sos2 but not with SLP-76. Moreover, tyrosine-phosphorylated LAT/pp36/38 in detergent lysates prepared from anti-CD3 stimulated T cells associated with Grb2 but not GrpL. These data reveal the presence of distinct complexes involving GrpL and Grb2 in T cells. A functional role of the GrpL-SLP-76 complex is suggested by the ability of GrpL to act alone or in concert with SLP-76 to augment NF-AT activation in Jurkat T cells.

Cbl-mediated negative regulation of the Syk tyrosine kinase. A critical role for Cbl phosphotyrosine-binding domain binding to Syk phosphotyrosine 323

The proto-oncogene product Cbl has emerged as a potential negative regulator of the Syk tyrosine kinase; however, the nature of physical interactions between Cbl and Syk that are critical for this negative regulation remains unclear. Here we show that the phosphotyrosine-binding (PTB) domain within the N-terminal transforming region of Cbl (Cbl-N) binds to phosphorylated Tyr323 in the linker region between the Src homology 2 and kinase domains of Syk, confirming recent results by another laboratory using the yeast two-hybrid approach (Deckert, M., Elly, C., Altman, A., and Liu, Y. C. (1998) J. Biol. Chem. 273, 8867-8874). A PTB domain-inactivating point mutation (G306E), corresponding to a loss-of-function mutation in the Caenorhabditis elegans Cbl homologue SLI-1, severely compromised Cbl-N/Syk binding in vitro and Cbl/Syk association in transfected COS-7 cells. Using heterologous expression in COS-7 cells, we investigated the role of Cbl PTB domain binding to Syk Tyr323 in the negative regulation of Syk. Co-expression of Cbl with Syk in COS-7 cells led to a dose-dependent decrease in the autophosphorylated pool of Syk and in phosphorylation of an in vivo substrate, CD8-zeta. Unexpectedly, these effects were largely due to the loss of Syk protein. Both the decrease in Syk and CD8-zeta phosphorylation and reduction in Syk protein levels were blocked by either G306E mutation in Cbl or by Y323F mutation in Syk. These results demonstrate a critical role for the Cbl PTB domain in the recruitment of Cbl to Syk and in Cbl-mediated negative regulation of Syk.

OPG/FDCR-1, a TNF receptor family member, is expressed in lymphoid cells and is up-regulated by ligating CD40

We have cloned a TNFR family member from a follicular dendritic cell (FDC)-like cell line, FDC-1. This molecule, FDC-derived receptor-1 (FDCR-1), is identical to osteoprotegerin (OPG), a soluble cytokine that regulates osteoclast differentiation. Recently, OPG/FDCR-1 has been characterized as a second receptor for receptor activator of NF-kappaB ligand (RANKL)/TNF-related activation-induced cytokine (TRANCE), a primarily T-cell restricted TNF family member that augments dendritic cell (DC) function. In this report, we demonstrate that OPG/FDCR-1 is membrane bound on the surface of transfected baby hamster kidney (BHK) and untransfected FDC-1 cells. We also found a restricted OPG/FDCR-1 expression pattern in lymphoid cells, specifically in B cells, DCs and FDC-enriched fractions, which in B cells and DCs is up-regulated by CD40 stimulation. Because OPG/FDCR-1 shares some properties with RANK, the first RANKL/TRANCE receptor, we discuss how the balance between RANK and OPG/FDCR-1 expression could influence immune responses and, ultimately, germinal center formation.

Different protein tyrosine kinases are required for B cell antigen receptor-mediated activation of extracellular signal-regulated kinase, c-Jun NH2-terminal kinase 1, and p38 mitogen-activated protein kinase

B cell antigen receptor (BCR) cross-linking activates three distinct families of nonreceptor protein tyrosine kinases (PTKs): src-family kinases, Syk, and Btk; these PTKs are responsible for initiating downstream events. BCR cross-linking in the chicken DT40 B cell line also activates three distinct mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase (ERK)2, c-jun NH2-terminal kinase (JNK)1, and p38 MAPK. To dissect the functional roles of these PTKs in MAPK signaling, activation of MAPKs was examined in various PTK-deficient DT40 cells. BCR-mediated activation of ERK2, although maintained in Lyn-deficient cells, was abolished in Syk-deficient cells and partially inhibited in Btk-deficient cells, indicating that BCR-mediated ERK2 activation requires Syk and that sustained ERK2 activation requires Btk. BCR-mediated JNK1 activation was maintained in Lyn-deficient cells but abolished in both Syk- and Btk-deficient cells, suggesting that JNK1 is activated via a Syk- and Btk-dependent pathway. Consistent with this, BCR-mediated JNK1 activation was dependent on intracellular calcium and phorbol myristate acetate-sensitive protein kinase Cs. In contrast, BCR-mediated p38 MAPK activation was detected in all three PTK-deficient cells, suggesting that no single PTK is essential. However, BCR-mediated p38 MAPK activation was abolished in Lyn/Syk double deficient cells, demonstrating that either Lyn or Syk alone may be sufficient to activate p38 MAPK. Our data show that BCR-mediated MAPK activation is regulated at the level of the PTKs.

Involvement of guanosine triphosphatases and phospholipase C-gamma2 in extracellular signal-regulated kinase, c-Jun NH2-terminal kinase, and p38 mitogen-activated protein kinase activation by the B cell antigen receptor

Mitogen-activated protein (MAP) kinase family members, including extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase ( JNK), and p38 MAP kinase, have been implicated in coupling the B cell antigen receptor (BCR) to transcriptional responses. However, the mechanisms that lead to the activation of these MAP kinase family members have been poorly elucidated. Here we demonstrate that the BCR-induced ERK activation is reduced by loss of Grb2 or expression of a dominant-negative form of Ras, RasN17, whereas this response is not affected by loss of Shc. The inhibition of the ERK response was also observed in phospholipase C (PLC)-gamma2-deficient DT40 B cells, and expression of RasN17 in the PLC-gamma2-deficient cells completely abrogated the ERK activation. The PLC-gamma2 dependency of ERK activation was most likely due to protein kinase C (PKC) activation rather than calcium mobilization, since loss of inositol 1,4,5-trisphosphate receptors did not affect ERK activation. Similar to cooperation of Ras with PKC activation in ERK response, both PLC-gamma2-dependent signal and GTPase are required for BCR-induced JNK and p38 responses. JNK response is dependent on Rac1 and calcium mobilization, whereas p38 response requires Rac1 and PKC activation.

p38 MAPK is required for CD40-induced gene expression and proliferation in B lymphocytes

We have investigated the activation of the p38 MAPK pathway in response to CD40 engagement in multiple B cell lines and in human tonsillar B cells to define the role of p38 MAPK in proliferation, NF-kappaB activation and gene expression. Cross-linking CD40 rapidly stimulates both p38 MAPK and its downstream effector, MAPKAPK-2. Inhibition of p38 MAPK activity in vivo with the specific cell-permeable inhibitor, SB203580, under conditions that completely prevented MAPKAPK-2 activation, strongly perturbed CD40-induced tonsillar B cell proliferation while potentiating the B cell receptor (BCR)-driven proliferative response. SB203580 also significantly reduced expression of a reporter gene driven by a minimal promoter containing four NF-kappaB elements, indicating a requirement for the p38 MAPK pathway in CD40-induced NF-kappaB activation. However, CD40-mediated NF-kappaB binding was not affected by SB203580, suggesting that NF-kappaB may not be a direct target for the CD40-induced p38 MAPK pathway. In addition, SB203580 selectively reduced CD40-induced CD54/ICAM-1 expression, whereas CD40-dependent expression of CD40 and CD95/Fas and four newly defined CD40-responsive genes cIAP2, TRAF1, TRAF4/CART and DR3 were unaffected. Our observations show that the p38 MAPK pathway is required for CD40-induced proliferation and that CD40 induces gene expression via both p38 MAPK-dependent and -independent pathways.

Two regions in the CD80 cytoplasmic tail regulate CD80 redistribution and T cell costimulation

CD28 is a major T cell costimulatory molecule, delivering signals distinct from those of the CD3/TCR complex, which regulate cytokine and cytokine receptor expression, cell proliferation, and cell viability. CD28 needs to be cross-linked to initiate signals, yet both of its ligands, CD80 and CD86, are expressed as monomers. Previously, we determined the cytoplasmic tail of CD80 is required for CD28-mediated costimulation and subcellular relocalization of CD80 in lymphocytes. In this study, we report that Reh B cell transfectants expressing CD80 with mutations in the cytoplasmic tail region either at 275-278 (RRNE-->AAAA, CD80/4A) or serine 284 (S-->A, CD80/SA) can bind ligand similar to transfectants expressing wild-type CD80, yet are unable to costimulate T cell proliferation. These mutant CD80 molecules are expressed on the surface of the Reh cells in small clusters or foci indistinguishable from those of wild-type CD80 molecules. However, mutant CD80 molecules unlike wild-type CD80 cannot be readily induced by ligand into caps. Thus, small clusters of CD80 found on APC are insufficient to initiate CD28-mediated signals, and the formation of CD80 caps appears to be a critical factor regulating the initiation of T cell costimulation. A 30-kDa phosphoprotein that associates with the cytoplasmic tail of CD80 in activated cells may play a role in CD80 redistribution and thus CD28-mediated costimulation. These results indicate two distinct regions of the CD80 cytoplasmic tail regulate its costimulatory function, and both regions are required for CD80 function.

The BB1 monoclonal antibody recognizes both cell surface CD74 (MHC class II-associated invariant chain) as well as B7-1 (CD80), resolving the question regarding a third CD28/CTLA-4 counterreceptor

The identification of all CD28/CTLA-4 counterreceptors is critical to our understanding of this pivotal pathway of T cell activation. Clouding our understanding has been the reported discrepancies in expression and function of the B7-1 (CD80) molecule based upon the use of the BB1 vs other anti-B7-1 mAbs. To resolve this issue, we have cloned a BB1-binding molecule from the BB1+B7-1(-) NALM-6 pre-B cell line. Here, we demonstrate that this BB1-binding molecule is identical to the cell surface form of CD74 (MHC class II-associated invariant chain). CD74-transfected cells bound the BB1 mAb but not other anti-CD80 mAbs, CD28-Ig, or CTLA4Ig. Absorption and blocking experiments confirmed the reactivity of BB1 mAb with CD74. A region of weak homology was identified between CD74 and the region of B7-1 encoding the BB1 epitope. Therefore, the BB1 mAb binds to a protein distinct from B7-1, and this epitope is also present on the B7-1 protein. Many of the puzzling observations in the literature concerning the expression of human B7-1 are resolved by an understanding that BB1 staining is the summation of CD74 plus B7-1 expression. This observation requires the field to reconsider studies using BB1 mAb in the analysis of CD80 expression and function.

Integrin-mediated signals regulated by members of the rho family of GTPases

The organization of the actin cytoskeleton can be regulated by soluble factors that trigger signal transduction events involving the Rho family of GTPases. Since adhesive interactions are also capable of organizing the actin-based cytoskeleton, we examined the role of Cdc42-, Rac-, and Rho-dependent signaling pathways in regulating the cytoskeleton during integrin-mediated adhesion and cell spreading using dominant-inhibitory mutants of these GTPases. When Rat1 cells initially adhere to the extracellular matrix protein fibronectin, punctate focal complexes form at the cell periphery. Concomitant with focal complex formation, we observed some phosphorylation of the focal adhesion kinase (FAK) and Src, which occurred independently of Rho family GTPases. However, subsequent phosphorylation of FAK and paxillin occurs in a Rho-dependent manner. Moreover, we found Rho dependence of the assembly of large focal adhesions from which actin stress fibers radiate. Initial adhesion to fibronectin also stimulates membrane ruffling; we show that this ruffling is independent of Rho but is dependent on both Cdc42 and Rac. Furthermore, we observed that Cdc42 controls the integrin-dependent activation of extracellular signal-regulated kinase 2 and of Akt, a kinase whose activity has been demonstrated to be dependent on phosphatidylinositol (PI) 3-kinase. Since Rac-dependent membrane ruffling can be stimulated by PI 3-kinase, it appears that Cdc42, PI 3-kinase, and Rac lie on a distinct pathway that regulates adhesion-induced membrane ruffling. In contrast to the differential regulation of integrin-mediated signaling by Cdc42, Rac, and Rho, we observed that all three GTPases regulate cell spreading, an event that may indirectly control cellular architecture. Therefore, several separable signaling pathways regulated by different members of the Rho family of GTPases converge to control adhesion-dependent changes in the organization of the cytoskeleton, changes that regulate cell morphology and behavior.

A comparison of signaling requirements for apoptosis of human B lymphocytes induced by the B cell receptor and CD95/Fas

To define how the signaling pathways that mediate the B cell receptor (BCR) death pathway differ from those responsible for CD95/Fas-mediated death, we compared the BCR and Fas death pathways in two human B cell lines, B104 and BJAB. Both BCR- and Fas-induced apoptosis are blocked by the peptide cysteine protease inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (ZVAD (mlz)), demonstrating a common requirement caspase activity. Despite this common characteristic, the ability of actinomycin D and cycloheximide to block BCR-induced apoptosis, but not apoptosis induced by Fas cross-linking, suggests that a major difference between these two pathways is their differential requirements for new gene and protein synthesis. BCR- and Fas-mediated apoptosis are both accompanied by activation of stress-activated protein kinase and p38 mitogen-activated protein kinase (MAPK). Activation of both stress-activated protein kinase and p38 MAPK was inhibited by ZVAD (mlz), suggesting the involvement of caspases. To determine the role of p38 MAPK activation in BCR- and Fas-induced apoptosis, we employed SB203580, a specific inhibitor of p38 MAPK. SB203580 inhibited BCR-induced apoptosis, but not apoptosis induced by cross-linking Fas. Furthermore, both actinomycin D and SB203580 inhibited BCR-induced, but not Fas-induced, activation of caspase. Collectively, these findings establish a role for p38 MAPK in BCR-induced apoptosis both upstream and downstream of caspase activity. The p38 MAPK pathway may function to regulate transcriptional or translational events that are critical for BCR-induced apoptosis.

Caspase-mediated activation and induction of apoptosis by the mammalian Ste20-like kinase Mst1

Mst1 is a ubiquitously expressed serine-threonine kinase, homologous to the budding yeast Ste20, whose physiological regulation and cellular function are unknown. In this paper we show that Mst1 is specifically cleaved by a caspase 3-like activity during apoptosis induced by either cross-linking CD95/Fas or by staurosporine treatment. CD95/Fas-induced cleavage of Mst1 was blocked by the cysteine protease inhibitor ZVAD-fmk, the more selective caspase inhibitor DEVD-CHO and by the viral serpin CrmA. Caspase-mediated cleavage of Mst1 removes the C-terminal regulatory domain and correlates with an increase in Mst1 activity in vivo, consistent with caspase-mediated cleavage activating Mst1. Overexpression of either wild-type Mst1 or a truncated mutant induces morphological changes characteristic of apoptosis. Furthermore, exogenously expressed Mst1 is cleaved, indicating that Mst1 can activate caspases that result in its cleavage. Kinase-dead Mst1 did not induce morphological alterations and was not cleaved upon overexpression, indicating that Mst1 must be catalytically active in order to mediate these effects. Mst1 activates MKK6, p38 MAPK, MKK7 and SAPK in co-transfection assays, suggesting that Mst1 may activate these pathways. Our findings suggest the existence of a positive feedback loop involving Mst1, and possibly the SAPK and p38 MAPK pathways, which serves to amplify the apoptotic response.

Polygenic autoimmune traits: Lyn, CD22, and SHP-1 are limiting elements of a biochemical pathway regulating BCR signaling and selection

A B lymphocyte hyperactivity syndrome resembling systemic lupus erythematosus characterizes mice lacking the src-family kinase Lyn. Lyn is not required to initiate B cell antigen receptor (BCR) signaling but is an essential inhibitory component. lyn-/- B cells have a delayed but increased calcium flux and exaggerated negative selection responses in the presence of antigen and spontaneous hyperactivity in the absence of antigen. As in invertebrates, genetic effects of loci with only one functional allele can be used to analyze signaling networks in mice, demonstrating that negative regulation of the BCR is a complex quantitative trait in which Lyn, the coreceptor CD22, and the tyrosine phosphatase SHP-1 are each limiting elements. The biochemical basis of this complex trait involves a pathway requiring Lyn to phosphorylate CD22 and recruit SHP-1 to the CD22/BCR complex.

Role for CD40-mediated activation of c-Rel and maintenance of c-myc RNA levels in mitigating anti-IgM-induced growth arrest

CD40 crosslinking on B cells activates NF-kappaB and stress-activated protein kinase (SAPK) pathways. Since CD40 crosslinking rescues WEHI 231 B cells from anti-IgM-induced apoptosis, those pathways were likely candidates to be involved. Indeed, both signaling cascades predominated in anti-IgM-treated WEHI 231 cells, treated concurrently with anti-CD40 to rescue them from apoptosis. Crosslinking of CD40 activated the NF-kappaB proteins c-Rel and p50, but had no influence on their cytoplasmic steady state level. However, in contrast to-and even in the presence of-anti-IgM-mediated signals, engagement of CD40 resulted in a prolonged nuclear translocation of c-Rel, thereby allowing the formation of active NF-kappaB complexes. Consistent with this, the upstream regulatory element of the c-myc promoter, known to be regulated by NF-kappaB, was differently regulated after BCR ligation vs BCR plus CD40 crosslinking. The level of c-myc RNA was rapidly downregulated after BCR engagement, but persistent in the presence of CD40 signaling.

Role of dendritic and follicular dendritic cells in HIV infection and pathogenesis

Dendritic cells (DCs) and follicular dendritic cells (FDCs) play important roles in HIV-mediated pathogenesis. Recent studies have defined new DC subsets and shown that DCs in lymphoid mucosa can both harbor virus and stimulate its spread into CD4(+) T cells. FDCs harbor unspliced HIV mRNA and immune complexed virus, but not actively infectious virus, yet these cells are a key regulated reservoir of virions.