CD20-induced B cell death can bypass mitochondria and caspase activation

The apoptotic pathway activated by chimeric anti-CD20 monoclonal antibodies (rituximab, IDEC.C2B8) was analyzed using the Burkitt lymphoma cell line Ramos. Crosslinking of CD20 (CD20XL) induced apoptosis in Ramos cells, which involved loss of mitochondrial membrane potential (Deltapsi(m)), the release of cytochrome-c (cyt-c), and activation of caspases-9 and -3. Nevertheless, several lines of evidence showed that the apoptotic outcome did not depend on these events. First, under circumstances where Ramos cells display resistance to either CD95- or B cell receptor (BCR)-induced apoptosis, CD20XL-induced apoptosis was not affected, pointing to a distinct pathway. Second, the broad-spectrum caspase inhibitor zVAD-fmk prevented processing of caspase-9, -3 and PARP as well as DNA fragmentation, but did not block apoptosis as measured by annexin V staining, cell size and membrane integrity. Lastly, Bcl-2 overexpression blocked cyt-c release and the decrease in Deltapsi(m), and completely prevented CD95- or BCR-mediated apoptosis; however, it did not affect CD20XL-induced cell death. We conclude that although CD20XL can initiate the mitochondrial apoptosis pathway, CD20-induced apoptosis does not necessarily require active caspases and cannot be blocked by Bcl-2. Since most chemotherapeutic drugs require the activation of caspases to exert their cytotoxicity, these findings provide an important rationale for the use of CD20 mAbs in chemoresistant malignancies.

Tolerization of dendritic cells by T(S) cells: the crucial role of inhibitory receptors ILT3 and ILT4

Immunoglobulin-like transcript 3 (ILT3) and ILT4 belong to a family of inhibitory receptors expressed by human monocytes and dendritic cells. We show here that CD8+CD28(-) alloantigen-specific T suppressor (TS) cells induce the up-regulation of ILT3 and ILT4 on monocytes and dendritic cells, rendering these antigen-presenting cells (APCs) tolerogenic. Tolerogenic APCs show reduced expression of costimulatory molecules and induce antigen-specific unresponsiveness in CD4+ T helper cells. Studies of human heart transplant recipients showed that rejection-free patients have circulating TS cells, which induce the up-regulation of ILT3 and ILT4 in donor APCs. These findings demonstrate an important mechanism of immune regulation.

Expression and function of TRAF-3 splice-variant isoforms in human lymphoma cell lines

TRAF-3 gene products are signaling adaptor molecules required for lymphocytes to mediate T-dependent antibody responses in vivo. Previous work identified 8 splice-variant TRAF-3 mRNA species by RT-PCR that have the potential to encode novel isoforms, seven of which induce NF-kappaB activation when over-expressed in 293 cells. Here, their expression was characterized by RNAse protection assay, which showed the T cell line Jurkat D1.1 and the B cell lines BJAB, Daudi, and Raji each expressed mRNA encoding TRAF-3 splice-variants in approximately the same rank order (from highest to lowest); TRAF-3 Delta103aa, Delta83aa, full-length, Delta25aa, Delta52aa, Delta56aa, Delta27aa, and Delta221aa mRNA. The TRAF-3 Delta130aa mRNA was not detectable in any of the cell lines examined. The functional effect of over-expressing each TRAF-3 splice-variant on NF-kappaB activation was studied in the TRAF-5-responsive B cell line, BJAB. Of the seven TRAF-3 splice-variant isoforms that induce NF-kappaB activation in 293 cells, only TRAF-3 Delta27aa, Delta103aa, or Delta130aa induce NF-kappaB activation in BJAB cells. Together, these data indicate that a number of TRAF-3 splice-variant mRNAs are expressed and function in B and T lymphoma lines, which suggests that certain TRAF-3 splice-variant isoforms may participate in mediating the known functions of the TRAF-3 gene in lymphocytes.

fMRI-derived cortical maps for haptic shape, texture, and hardness

We used functional magnetic resonance imaging (fMRI) to investigate the neural substrates involved in haptic processing of texture, shape, and hardness. Subjects performed haptic classification tasks on a set of 27 silicone objects having parametrically defined shape, texture, and hardness. The objects were ellipsoids of revolution in which the ratio of the long to the short axis was varied, producing three different shapes. Three surface textures and three hardness levels were used. In three separate experiments, the same subjects classified each object along the three levels of one of the object properties (shape, texture, or hardness). Texture, shape, and hardness processing led to contralateral activation in the postcentral gyrus (PCG). A common region located within relatively posterior portions of the PCG was observed during shape and texture identification whereas a separate and more anterior region was activated during the hardness identification task. The hardness identification task also produced bilateral activation within the parietal operculum.

Induction of xenoreactive CD4+ T-cell anergy by suppressor CD8+CD28- T cells

BACKGROUND

The underlying mechanism of immune suppression mediated by regulatory T cells is not completely understood. In previous studies we have shown that antigen-specific human T suppressor cells (Ts) can be generated in vitro by multiple rounds of stimulation with allogeneic, xenogeneic, or antigen-pulsed autologous antigen-presenting cells (APC). Human Ts express the CD8+CD28- phenotype and require specific recognition of MHC class I/peptide complexes on the surface of APC to block proliferation of T helper cells (Th). The aim of the present study was to explore the activation requirements of Ts as well as the nature of Th unresponsiveness to xenogeneic (swine) antigens induced by Ts.

METHODS AND RESULTS

We investigated whether specific antigenic stimulation of Ts is required for their ability to inhibit early activation of xenoreactive Th (up-regulation of CD40 ligand). Flow cytometry studies indicated that Ts function required specific recognition of MHC class I on the surface of the stimulating APC. However, neither proliferation nor protein synthesis was required for the ability of Ts to inhibit Th. Ts drastically reduced the capacity of xenoreactive Th cells to produce interleukin (IL)-2 in response to the specific APC, without affecting their surface expression of IL-2 receptor. The suppressor effect that Ts exerted on Th proliferation could not be circumvented by CD40 ligation on the surface of the APC but could be reversed by the addition of exogenous IL-2.

CONCLUSION

These data indicate that Ts induce anergy of xenoreactive human Th cells upon specific recognition of MHC class I antigens. Hence, Ts may prevent the activation of T cell-mediated immune responses against xenogeneic transplants.

TRAF-3 interacts with p62 nucleoporin, a component of the nuclear pore central plug that binds classical NLS-containing import complexes

The TRAF-3 gene encodes a number of splice-variant isoforms that function as adapter molecules in NF-kappaB signaling, in part by associating with the cytoplasmic tails of CD40 or other TNF-receptor (TNF-R) family members. To identify downstream molecules in TRAF-3 signaling, a yeast two-hybrid library was screened with a full-length TRAF-3 construct. Nine independent TRAF-3 interacting clones encoded fragments of p62 Nucleoporin (p62), a 522 amino acid (aa) component of the nuclear pore central plug, that is known to bind karyopherin-beta/classical-NLS import factor complexes. The interaction of p62 with TRAF-3 was specific, since p62 failed to interact with TRAF-2, -4, -5, or -6. Deletional analysis in yeast revealed that the p62:TRAF-3 interaction is mediated by a p62 carboxy (C)-terminal coiled-coil domain and TRAF-3's fifth zinc (Zn) finger and coiled-coil domain. In human 293 T cells, recombinant TRAF-3 or p62 specifically co-immunoprecipitates the other species. In addition, endogenous p62 co-precipitates over-expressed TRAF-3. The functional effects of over-expressing a TRAF-3 binding fragment, p62(aa 336-522) were studied on NF-kappaB-dependent, or control STAT1-dependent reporter activity in 293 T cells, either resting or after stimulation by CD40 or IFN-gamma, respectively. Over-expression of p62(aa 336-522) induces NF-kappaB activation in resting cells and augments CD40-induced NF-kappaB activation, but has no effect on control STAT1 reporter activity, either at baseline or after IFN-gamma induction. The finding that TRAF-3 binds p62, suggests that TRAF-3 may serve as an adapter molecule at the nuclear membrane, in addition to its known adapter function at the plasma membrane.

T suppressor lymphocytes inhibit NF-kappa B-mediated transcription of CD86 gene in APC

CD8+CD28- human T suppressor cells (Ts) act on APC, inhibiting their ability to elicit Th activation and proliferation. This effect is due to inhibition of the CD40 pathway which normally leads to CD80 and CD86 up-regulation. To determine whether Ts inhibit expression of B7 molecules by blocking transcription, we cloned and characterized the CD86 promoter. Mutational analysis revealed that Ts inhibit transcription driven by the CD86 promoter. The NF-kappa B binding site, at -612 of the CD86 promoter, is essential for Th-induced transcription. In cultures containing Th and Ts, Ts inhibit Th-induced NF-kappa B activation in APC. Together, these findings indicate that Ts inhibition of NF-kappa B activation in APC is a means by which they regulate the activation and proliferation of Th.

Antigen presenting cells integrate opposing signals from CD4+ and CD8+ regulatory T lymphocytes to arbitrate the outcomes of immune responses

An individual's set of polymorphic HLA class II and I molecules is known to select the T cell repertoire in the thymus and to present processed antigenic peptides (pAg) to mature peripheral CD4+ T helper (Th) and CD8+ T cytotoxic (Th) cells in the periphery. This review highlights new studies which address how antigen presenting cells (APC) integrate the responses of cognate Th and T suppressor (Ts) cells to determine the outcome of immune responses. Together with other findings, these studies emphasize that understanding the mechanism of immune processes requires consideration of HLA molecules in the context of the peptides they bind, the antigen presenting cells (APC) that express them and the T lymphocytes that recognize them. The activities of lymphocyte and APC surface structures are becoming integrated into a physiological understanding of the cellular interactions between regulatory and effector T cells with APC.

Inhibition of CD40 signaling pathway in antigen presenting cells by T suppressor cells

Understanding the mechanism which underlies the induction of immunologic tolerance is crucial to the development of strategies for treatment of autoimmune diseases and allograft rejection. Although the concept that T suppressor cells (Ts) downregulate the immune response has long been accepted, the existence of a distinct population of lymphocytes that mediates suppression has not been convincingly demonstrated. In previous studies, we have utilized human T cell lines (TCLs) to analyze the suppressive effects of CD8+CD28 T cells in allogeneic, peptide specific and xeno-specific responses. In each case, CD8+CD28- T cells inhibit proliferation of CD4+ T helper lymphocytes (Th) with cognate antigen specificity. These CD8+CD28- T cells display the critical functional characteristics of T suppressor cells. Similar to the induction of CD8+ cytotoxic T cells (Tc) by Th, this process depends on antigen presenting cells (APC) acting as a "bridge" between MHC-class I specific CD8+ and class II specific CD4+ T cells. A possible explanation of Ts-mediated suppression is their ability to modulate the function of APCs. The present studies show that CD8+CD28- Ts directly inhibit the CD40 signaling pathway of APC by a contact-dependent mechanism that renders bridging APCs incapable of inducing CD4+ Th activation. The effects of Ts on the functional state of APC supports the concept that the order in which Ts and Th cells interact with cognate APCs determines the functional outcome of immune responses.

TRAF-3 mRNA splice-deletion variants encode isoforms that induce NF-kappaB activation

Although TRAF-3 gene products are required for signaling in T-B cell collaboration, full-length TRAF-3 appears to lack signaling function in transient transfection assays that measure NF-kappaB activation. However, the TRAF-3 gene also encodes at least three mRNA splice-deletion variants that predict protein isoforms (delta25aa, delta52aa and delta56aa) with altered zinc (Zn) finger domains and unknown functional capacities. To determine whether TRAF-3 splice-deletion variants may transmit activating receptor signals to the nucleus, cDNAs for five additional splice-variant isoforms (delta27aa, delta83aa, delta103aa, delta130aa and delta221aa) were cloned from a TRAF-3+ lymphoma and the expression and function of each of the eight TRAF-3 splice-deletion variants was analyzed. Among the splice-deletion variants, TRAF-3 delta130 mRNA is expressed by tonsillar B cells and by each of a panel of B and T cell lines. TRAF-3 delta221 protein is expressed by tonsillar B cells and by each of the lymphocytic lines. The functional effect of over-expressing each TRAF-3 splice-deletion variant on NF-kappaB activation was studied in 293 T cells. Seven of the TRAF-3 splice-deletion variants, such as TRAF-3 delta130, induce substantial NF-kappaB-driven luciferase activity (80-500 fold). In contrast, TRAF-3 delta221 (in which the complete Zn finger domain is absent) fails to induce NF-kappaB activation. Although full-length TRAF-3 alone is inactive, it augments the functional effects of the seven activating TRAF-3 splice-deletion variants (1.4-5 fold). These data indicate that alterations of the Zn finger domains render the TRAF-3 splice-deletion variants capable of inducing NF-kappaB activation and that full-length TRAF-3 augments their signaling.

An aggressive form of polyarticular arthritis in a man with CD154 mutation (X-linked hyper-IgM syndrome)

Hyper-IgM syndrome (HIM) is a rare immunodeficiency disorder that has been associated with the development of symptoms and clinical features characteristic of rheumatoid arthritis (RA). We describe a patient with HIM and severe erosive arthritis with prominent nodules in the absence of detectable serum rheumatoid factor. Because HIM results from defects in either T cell CD154 (CD40 ligand) expression or abnormal CD40 signaling, the molecular basis of the patient's disease was analyzed. Activated CD4+ T cells failed to express surface CD154 protein, and molecular analysis of CD154 complementary DNA revealed a nucleotide transversion resulting in the nonconservative amino acid substitution G-D at amino acid 257. This case indicates that defective CD154-dependent CD40 signaling can be associated with susceptibility to a severe inflammatory arthritis that has both similarities to and differences from idiopathic RA.

A single gene for human TRAF-3 at chromosome 14q32.3 encodes a variety of mRNA species by alternative polyadenylation, mRNA splicing and transcription initiation

Human TRAF-3 is a signaling molecule that interacts with the cytoplasmic tails of CD40 and other TNF-receptor family members. TRAF-3 mRNA is expressed as two major classes of approximately 2 and 8 kb and a number of TRAF-3 encoding cDNA clones differ in discrete gene segments. Because this variety of mRNA species could result from mRNA processing events and/or multiple genes, the structure and localization of TRAF-3 encoding gene elements were determined. FISH and radiation hybrid mapping demonstrated that TRAF-3 is located at chromosome 14q32.3, approximately 1 Mb centromeric to the Ig heavy chain gene complex. Physical mapping of four overlapping genomic PAC clones established that TRAF-3 transcripts are encoded by a single gene, comprised of 13 exons and spanning 130 kb. Alternative polyadenylation in the mRNA segment encoded by exon 12 accounts for the difference between the 2 kb and the 8 kb classes of transcripts. Alternative mRNA splicing in the coding region (encoded by exons 3-12) generates transcripts which delete exons 8 (75 nt), 7+8 (156 nt) or 8+9 (168 nt) and that encode distinct protein isoforms (delta25, delta52 and delta56 aa, respectively). Alternative splicing of exon 2 (139 nt) and alternative transcriptional initiation result in mRNA species with distinct 5'UTRs. Together, these data indicate that a single TRAF-3 gene encodes a variety of mRNA species by a combination of alternative polyadenylation, alternative mRNA splicing and/or alternative initiation.

Induction of MHC-class I restricted human suppressor T cells by peptide priming in vitro

The induction of regulatory T cells may offer an effective means for specific immunosuppression of autoimmune disease and allograft rejection. The existence of suppressor T cells has been previously documented, yet their mechanism of action remains poorly characterized. Our studies demonstrate that T suppressor (Ts) cell lines can be generated by in vitro immunization of human PBMCs, with synthetic peptides or soluble proteins coupled to beads. Such Ts cells express the CD8+CD28- phenotype and show the following characteristics: (a) antigen specificity and restriction by self MHC Class I molecules; (b) limited TCR V beta gene usage; (c) ability to inhibit antigen-specific, MHC Class II restricted, Th proliferative responses; and (d) capacity to downregulate and/or inhibit the upregulation by Th of CD40, CD80, and CD86 molecules on APCs. The inhibitory activity of Ts on Th proliferation requires the tripartite interaction between Th, Ts, and APCs and results from inefficient costimulation of Th.

Fas ligand is constitutively secreted by prostate cancer cells in vitro

LNCaP, DU145, and PC3 prostate carcinoma cells secrete the 27-kDa soluble Fas ligand (sFasL) into their local environment. sFasL arises from the 40-kDa membrane-bound form (mFasL), which can be found on the cell surface in the LNCaP line, as demonstrated by monoclonal antibody staining. mFasL was also found in extracts of all three cell lines, as demonstrated by Western blotting. FasL mRNA was detected not only in the cell lines, but in the normal prostate as well. sFasL protein could also be detected immunohistochemically in prostate secretions and in human semen. Cleavage of mFasL to sFasL could be inhibited by several matrix metalloprotease inhibitors without a change in the cellular levels of FasL. Prostate-derived sFasL is biologically active, as demonstrated by its induction of apoptosis in Fas-positive Ramos cells, which was detected by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. Mitoxantrone induces cellular apoptosis in all three prostate cancer cell lines. Mitoxantrone treatment and doxorubicin treatment also cause up-regulation of Fas, the cell surface receptor for FasL, in LNCaP cells, but not in DU145 or PC3 cells. Furthermore, the up-regulation of Fas expression by mitoxantrone at a high concentration was potentiated by hydrocortisone. When FasL interacts with its Fas, the Fas-bearing cell undergoes apoptosis. When LNCaP cells were treated with mitoxantrone and incubated with an anti-FasL monoclonal antibody, apoptosis was partially blocked. This not only further suggests that the sFasL is biologically active, but that the up-regulation of Fas in the presence of sFasL accounts, in part, for the cytotoxicity of mitoxantrone.

Intracerebroventricular injection of interleukin-1 suppresses peripheral lymphocyte function in the primate

The cytokine interleukin-1 (IL-1) can act within the brain to induce peripheral endocrine and immune effects. In the rodent intracerebroventricular (i.c.v.) injection of IL-1 activates the hypothalamic-pituitary-adrenal axis and suppresses peripheral immune function by a CRH-dependent mechanism. It is unknown if IL-1 can similarly act within the brain to cause peripheral immunosuppression in the primate and to what extent this could be attributed to the IL-1-induced increase in ACTH and cortisol levels. In this study we have characterized the pituitary-adrenal and peripheral lymphocyte responses to IL-1 alpha (4.2 micrograms) infused over 30 min into the lateral ventricle of ovariectomized monkeys (n = 5) as compared with responses to an intravenous (i.v.) ACTH infusion (1 microgram/h for 7 h; n = 4). Four serial blood samples were obtained for ACTH and cortisol determination and for lymphocyte isolation during a 1-hour baseline and for 7 h after IL-1 or ACTH. Lymphocyte proliferation was measured by 3H-thymidine uptake in response to stimulation with phytohemagglutinin. In all 5 animals, IL-1 alpha caused rapid and profound suppression of lymphocyte mitogen responsiveness for 7 h. Baseline lymphocyte proliferation was 51,800 +/- 9,780 cpm and suppressed to a nadir of 4.5% with a mean of 23% baseline over 7 h (p < 0.001). Mean ACTH and cortisol levels increased from 33 +/- (SEM) 4.6 pg/ml and 43 +/- 4.0 micrograms/dl, respectively, during the control period to 90 +/- 14 pg/ml and 56 +/- 2.6 micrograms/dl, respectively, after IL-1 (p < 0.01). Before i.v. ACTH, baseline lymphocyte proliferation was 49,400 +/- 2,820 cpm, and suppressed to a mean of 64% of baseline during ACTH infusion (p < 0.05). Mean ACTH and cortisol levels increased from 48 +/- 5.0 pg/ml and 43 +/- 2.0 micrograms/dl, respectively, to 170 +/- 34 pg/ml and 66 +/- 2.3 micrograms/dl, respectively, during the ACTH infusion (p < 0.01). Lymphocyte suppression after i.c.v. IL-1 was much more profound than after i.v. ACTH (p < 0.01); the area under the IL-1 response curve was 37% of the area under the ACTH response curve. These studies demonstrate for the first time in the primate that centrally injected IL-1 has a profound suppressive effect on lymphocyte function. They also show for the first time in any species that there appears to be a significant immunosuppressive message produced by i.c.v. IL-1 that is not accounted for by the associated increases in ACTH and cortisol.

Polydeoxyguanine motifs in a 12-mer phosphorothioate oligodeoxynucleotide augment binding to the v3 loop of HIV-1 gp120 and potency of HIV-1 inhibition independency of G-tetrad formation

Phosphorothioate oligodeoxynucleotides belong to a class of polyanions that bind to the third variable domain (v3) of HIV-1 gp120 and inhibit infectivity of a wide variety of HIV-1 isolates. This potent v3 binding of phosphorothioate oligodeoxynucleotides, which is relatively independent of the nucleotide sequence of the oligodeoxynucleotides, decreases with chain length (below 18-mers) and is low for 8-mers. However, recent studies have observed a nucleotide sequence-dependent augmentation of phosphorothioate oligodeoxynucleotide binding to v3 for 8-mers that contain the S-dG4 motif (e.g., SdT2G4T2) and have suggested that formation of quadruple helical tetraplexes (G-tetrads) is associated with the acquisition of v3 binding ability by small phosphorothioate oligodeoxynucleotides. In the current study, a series of SdG4-containing oligodeoxynucleotides were synthesized with varying tandem length (including the 8-mer SdT2G4T2, the 12-mer SdG4T4G4, and the 28-mer SdG4(T4G4)3) and compared with phosphorothioate oligodeoxynucleotides (with similar lengths or related sequences) for (1) their inhibition of the binding of mAb 9284, which binds to the N-terminal portion of the v3 loop, (2) the values of Kc when these compounds are used as competitors of the rgp120-binding of an alkylating phosphodiester oligodeoxynucleotide probe, and (3) inhibition of HIV-1 infectivity in a cell-cell transmission model. The presence of S-dG4 motifs and the number of tandem motifs augmented v3 binding and anti-HIV-1 infectivity for small (8-mer or 12-mer oligodeoxynucleotides) but did not significantly augment the potency of 28-mers. Whereas tetraplex formation of SdT2G4T2 may contribute to its v3 binding, the 12-mer SdG4T4G4 does not migrate as the tetraplex on nonreducing gels, suggesting that S-dG4 motifs may augment anti-HIV activity by multiple mechanisms.

The central role of the CD40-ligand and CD40 pathway in T-lymphocyte-mediated differentiation of B lymphocytes

This review summarizes recent findings concerning the role of CD40-ligand and CD40 interactions in B-cell differentiation. CD40-ligand on helper CD4+ T lymphocytes interacts with CD40 on B cells and directs the selection and differentiation of clones of B lymphocytes to generate specific antibody-dependent immune responses. CD40-ligand is necessary for normal B-cell differentiation and plays several distinctive roles in this multistage process. The CD40 signaling pathway that normally regulates B-cell death appears to be usurped by the Epstein-Barr virus to mediate B-cell transformation.

2 A crystal structure of an extracellular fragment of human CD40 ligand

BACKGROUND

The CD40 ligand (CD40L) is a member of the tumor necrosis factor (TNF) family of proteins and is transiently expressed on the surface of activated T cells. The binding of CD40L to CD40, which is expressed on the surface of B cells, provides a critical and unique pathway of cellular activation resulting in antibody isotype switching, regulation of apoptosis, and B cell proliferation and differentiation. Naturally occurring mutations of CD40L result in the clinical hyper-IgM syndrome, characterized by an inability to produce immunoglobulins of the IgG, IgA and IgE isotypes.

RESULTS

We have determined the crystal structure of a soluble extracellular fragment of human CD40L to 2 A resolution and with an R factor of 21.8%. Although the molecule forms a trimer similar to that found for other members of the TNF family, such as TNF alpha and lymphotoxin-alpha, and exhibits a similar overall fold, there are considerable differences in several loops including those predicted to be involved in CD40 binding.

CONCLUSIONS

The structure suggests that most of the hyper-IgM syndrome mutations affect the folding and stability of the molecule rather than the CD40-binding site directly. Despite the fact that the hyper-IgM syndrome mutations are dispersed in the primary sequence, a large fraction of them are clustered in space in the vicinity of a surface loop, close to the predicted CD40-binding site.

Opposing roles of CD95 (Fas/APO-1) and CD40 in the death and rescue of human low density tonsillar B cells

The regulation of B cell death plays roles in the selection of Ag-specific B cells in humoral immune responses, controlling B cell homeostasis and perhaps limiting transformation. The present work addresses whether CD95 induces tonsillar B cells to undergo apoptosis and, if so, whether contact-dependent CD40-L:CD40 signaling can rescue tonsillar B cells from CD95-induced apoptosis. CD95 triggering by anti-CD95 mAb (APO-1) was studied in human tonsillar B cell populations that were separated by density centrifugation into fractions enriched for either low density, CD38+ B cells or high density, resting B cells. Low density tonsillar B cells express CD95 and undergo anti-CD95-mediated apoptosis by analysis of cellular morphology or DNA fragmentation by TUNEL assay. The induction of apoptosis in low density tonsillar B cells by anti-CD95 mAb is inhibited by CD40 signals provided by stably transfected CD40-L+ 293 cells, but not by control transfected 293 cells (expressing CD8). In addition, the rescuing effect of CD40-L+ cells is inhibited specifically by anti-CD40-L (mAb 5c8). The counteracting effects of CD95 and CD40 signaling were also studied in Ramos 2G6, a homogeneous B cell tumor line of germinal center phenotype that expresses CD95 and CD40. Similar to the behavior of low density tonsillar B cells, Ramos 2G6 undergoes anti-CD95-mediated apoptosis, which is prevented by CD40-mediated rescue. These data show that CD95 induces apoptosis in low density tonsillar B cells and that CD40-L:CD40 interactions rescue low density tonsillar B cells or the B cell tumor Ramos 2G6 from CD95-induced apoptosis, and suggest roles for CD95 and CD40 in B cell death and selection, respectively.

Opposing roles of CD95 (Fas/APO-1) and CD40 in the death and rescue of human low density tonsillar B cells

The regulation of B cell death plays roles in the selection of Ag-specific B cells in humoral immune responses, controlling B cell homeostasis and perhaps limiting transformation. The present work addresses whether CD95 induces tonsillar B cells to undergo apoptosis and, if so, whether contact-dependent CD40-L:CD40 signaling can rescue tonsillar B cells from CD95-induced apoptosis. CD95 triggering by anti-CD95 mAb (APO-1) was studied in human tonsillar B cell populations that were separated by density centrifugation into fractions enriched for either low density, CD38+ B cells or high density, resting B cells. Low density tonsillar B cells express CD95 and undergo anti-CD95-mediated apoptosis by analysis of cellular morphology or DNA fragmentation by TUNEL assay. The induction of apoptosis in low density tonsillar B cells by anti-CD95 mAb is inhibited by CD40 signals provided by stably transfected CD40-L+ 293 cells, but not by control transfected 293 cells (expressing CD8). In addition, the rescuing effect of CD40-L+ cells is inhibited specifically by anti-CD40-L (mAb 5c8). The counteracting effects of CD95 and CD40 signaling were also studied in Ramos 2G6, a homogeneous B cell tumor line of germinal center phenotype that expresses CD95 and CD40. Similar to the behavior of low density tonsillar B cells, Ramos 2G6 undergoes anti-CD95-mediated apoptosis, which is prevented by CD40-mediated rescue. These data show that CD95 induces apoptosis in low density tonsillar B cells and that CD40-L:CD40 interactions rescue low density tonsillar B cells or the B cell tumor Ramos 2G6 from CD95-induced apoptosis, and suggest roles for CD95 and CD40 in B cell death and selection, respectively.

Ligation of CD40 on fibroblasts induces CD54 (ICAM-1) and CD106 (VCAM-1) up-regulation and IL-6 production and proliferation

CD40 was originally described as a functionally significant B cell surface molecule. However, CD40 is also expressed on monocytes, dendritic cells, epithelial cells, and basophils. We now report that synovial membrane (SM) or dermal fibroblasts also express cell surface CD40 in vitro. Fibroblast CD40 expression declines with increasing time in culture and recombinant interferon-gamma (rINF-gamma) induces fibroblast CD40 up-regulation. This effect of rINF-gamma is augmented by recombinant interleukin-1 alpha or recombinant tumor necrosis factor-alpha. CD40 expression on fibroblasts is functionally significant because CD40L-CD40 interactions induce SM fibroblast CD54 (intercellular adhesion molecule-1) and CD106 (vascular cell adhesion molecule-1) up-regulation. Moreover, ligation of CD40 augments IL-6 production by SM fibroblasts and induces fibroblasts to proliferate. In addition, rINF-gamma enhances the effect of CD40L-CD40 interactions on fibroblast proliferation. Taken together, these studies show that fibroblasts can express CD40, cytokines can regulate fibroblast CD40 expression, and CD40 ligation induces fibroblast activation and proliferation.

Involvement of CRAF1, a relative of TRAF, in CD40 signaling

CD40 is a receptor on the surface of B lymphocytes, the activation of which leads to B cell survival, growth, and differentiation. A yeast two-hybrid screen identified a gene, CRAF1, encoding a protein that interacts directly with the CD40 cytoplasmic tail through a region of similarity to the tumor necrosis factor-alpha (TNF-alpha) receptor-associated factors. Overexpression of a truncated CRAF1 gene inhibited CD40-mediated up-regulation of CD23. A region of CRAF1 was similar to the TNF-alpha receptor-associated factors TRAF1 and TRAF2 and so defined a shared TRAF-C domain that was necessary and sufficient for CD40 binding and homodimerization. The CRAF1 sequence also predicted a long amphipathic helix, a pattern of five zinc fingers, and a zinc ring finger. It is likely that other members of the TNF receptor superfamily use CRAF-related proteins in their signal transduction processes.

CD40 ligand (CD40L) expression and B cell function in agammaglobulinemia with normal or elevated levels of IgM (HIM). Comparison of X-linked, autosomal recessive, and non-X-linked forms of the disease, and obligate carriers

Hyper-IgM syndrome is a rare immunodeficiency characterized by low or absent IgG, IgA, and IgE with normal or elevated levels of IgM. It can occur as an acquired or familial disorder with either X-linked or autosomal modes of inheritance. The X-linked form (HIGM1) is a result of mutations in the CD40 ligand (CD40L) gene, but the defect in non-X-linked forms of the disease (HIM) has not been determined. We show here that CD40L expression on activated T cells from non-X-linked patients can be detected by CD40Fc, 5c8 Mab, and anti-TRAP, whereas activated T cells from HIGM1 patients either had no detectable CD40L (Type I), or stained with anti-TRAP but not CD40Fc or 5c8 (Type II). Activated T cells from obligate carriers varied from low to normal expression of CD40L. B cells from HIGM1 and non-X-linked HIM patients proliferated in response to CD40L. Costimulation of B cells from HIGM1, from sporadic HIM, or from non-X-linked HIM patients with CD40L plus IL-2 resulted in some IgM production, but no significant IgG or IgA. Costimulation with CD40L plus IL-10 resulted in significant IgG and/or IgA secretion by B cells from some HIGM1 patients, but consistently failed to stimulate IgG or IgA secretion by B cells from non-X-linked patients. In addition, costimulation with CD40L and IL-4 failed to induce IgE secretion by B cells from one non-X-linked HIM patient, and induced a weak response in another. These results suggest that patients with non-X-linked forms of HIM may have an intrinsic B cell defect preventing heavy chain switching, which is not related to expression of CD40L.

CD40 ligand (CD40L) expression and B cell function in agammaglobulinemia with normal or elevated levels of IgM (HIM). Comparison of X-linked, autosomal recessive, and non-X-linked forms of the disease, and obligate carriers

Hyper-IgM syndrome is a rare immunodeficiency characterized by low or absent IgG, IgA, and IgE with normal or elevated levels of IgM. It can occur as an acquired or familial disorder with either X-linked or autosomal modes of inheritance. The X-linked form (HIGM1) is a result of mutations in the CD40 ligand (CD40L) gene, but the defect in non-X-linked forms of the disease (HIM) has not been determined. We show here that CD40L expression on activated T cells from non-X-linked patients can be detected by CD40Fc, 5c8 Mab, and anti-TRAP, whereas activated T cells from HIGM1 patients either had no detectable CD40L (Type I), or stained with anti-TRAP but not CD40Fc or 5c8 (Type II). Activated T cells from obligate carriers varied from low to normal expression of CD40L. B cells from HIGM1 and non-X-linked HIM patients proliferated in response to CD40L. Costimulation of B cells from HIGM1, from sporadic HIM, or from non-X-linked HIM patients with CD40L plus IL-2 resulted in some IgM production, but no significant IgG or IgA. Costimulation with CD40L plus IL-10 resulted in significant IgG and/or IgA secretion by B cells from some HIGM1 patients, but consistently failed to stimulate IgG or IgA secretion by B cells from non-X-linked patients. In addition, costimulation with CD40L and IL-4 failed to induce IgE secretion by B cells from one non-X-linked HIM patient, and induced a weak response in another. These results suggest that patients with non-X-linked forms of HIM may have an intrinsic B cell defect preventing heavy chain switching, which is not related to expression of CD40L.

Phenotypic and functional characterization of T-BAM (CD40 ligand)+ T-cell non-Hodgkin's lymphoma

The precise mechanisms regulating T-helper function have been intensively investigated. We and others have recently identified a new T-cell-B-cell-activating molecule called T-BAM that directs B-cell differentiation by interacting with the CD40 molecule on B cells. Using a specific monoclonal antibody against T-BAM (5C8), we have previously shown that T-BAM expressing T cells are predominantly CD4+CD8- and in normal lymphoid tissue have a unique distribution. However, no information has been obtained regarding the phenotype and functional properties of human neoplastic T cells. Therefore, we investigated T-BAM expression immunohistochemically in 87 well-characterized T-cell non-Hodgkin's lymphomas and lymphoid leukemias (LL). We found that 21/81 neoplasms expressed detectable T-BAM and these positive tumors belong almost exclusively to the CD4+CD8- subtype. In addition, to determine whether T-BAM expression could be induced on T-BAM-LL cells, we activated T-BAM-LLs in vitro and showed that T-BAM could be upregulated only in CD4+CD8- tumors. Our studies clearly show that T-BAM is constitutively expressed in a large number of T-cell neoplasms with a relative mature phenotype (CD4+CD8-) and that only CD4+ neoplastic T cells can be induced in vitro to express this molecule. Additional studies are necessary to identify the biologic significance of T-BAM expression and its potential and clinical implications.

Isolation of cDNAs encoding T-BAM, a surface glycoprotein on CD4+ T cells mediating contact-dependent helper function for B cells: identity with the CD40-ligand

"T-cell B-cell Activating Molecule" (T-BAM) is an activation-induced surface protein on CD4+ T cells that mediates a contact-dependent signal for B cell differentiation and immunoglobulin (Ig) secretion. The T-BAM protein on a helper clone of Jurkat (D1.1) was affinity purified using the anti-T-BAM mAb, 5c8. The NH2-terminal amino acid sequence of purified T-BAM was determined and found to be highly homologous to the predicted NH2-terminal sequence of a T cell ligand to the B cell CD40 molecule (CD40-L). From a D1.1 cDNA library, a clone was isolated that encodes CD40-L by sequence and drives expression of T-BAM protein on transfected cells, demonstrating that the T-BAM and CD40-L genes and proteins are identical. Moreover, transfection of T-BAM was shown to confer to non-lymphoid cells, the ability to induce B cells to upregulate the expression of surface CD23 molecules. In previous studies we showed that T-BAM was expressed predominantly on activated CD4+ and on few if any CD8+ cells. Although the current work confirms that T-BAM is largely restricted to activated CD4+ T cells, we now provide definitive evidence that T-BAM can be expressed by a small population of CD8+ T cells after activation. Importantly, a subset of CD8+ T cells do not express T-BAM after activation and this T-BAM- phenotype is maintained on certain CD8+ T cell clones. Taken together, these data unify the biology and structure of T-BAM and CD40-L and this synthesis has implications for understanding the T cell regulation of the humoral immune response.

T-BAM/CD40-L on helper T lymphocytes augments lymphokine-induced B cell Ig isotype switch recombination and rescues B cells from programmed cell death

An important component of T cell help for B lymphocyte differentiation is the contact-dependent signaling mediated by the T cell-B cell activating molecule (T-BAM/CD40-L), an activation-induced surface membrane protein on CD4+ T helper cells in lymphoid follicles that interacts with the B cell surface molecule, CD40. The present study dissects the roles of T-BAM/CD40-L in helper function by means of a neutralizing anti-T-BAM/CD40-L mAb (5c8), a T-BAM/CD40-L-expressing T cell tumor subclone (Jurkat D1.1), and a T-BAM/CD40-L-responsive IgM+ B cell tumor of germinal center origin (RAMOS 266). Like activated T cells, D1.1 cells induce B cells to synthesize IgG, IgA, and IgE in a process that is specifically inhibited by the mAb 5c8. Although rIL-4 alone, but not Jurkat D1.1, induces IgH C gamma mRNA transcripts in RAMOS 266, the T-BAM/CD40-L molecule on D1.1 acts on rIL-4-primed RAMOS B cells to augment expression of C gamma transcripts. In addition, IgG+ RAMOS 266 clones were expanded from D1.1- and rIL-4-stimulated cultures that had undergone deletional IgH isotype switch recombination events. Furthermore, T-BAM/CD40-L signals delivered by the D1.1 clone dramatically rescue RAMOS 266 from mAb anti-IgM-induced apoptosis. Taken together, these data support the idea that T-BAM/CD40-L plays important roles in inducing Ig isotype switch recombination and the clonal selection of isotype-switched B cells.

Characteristics of HIV-1 gp120 glycoprotein binding to glycolipids

We examined the binding of the gp120 envelope glycoprotein (gp120) of the human immunodeficiency virus (HIV-1) to sulfatide (GalS), galactocerebroside (GalC), and GM1-ganglioside (GM1). The gp120 glycoprotein bound to GalS but not to GalC or GM1 by enzyme-linked immunosorbent assay (ELISA) and by an immunospot assay on nitrocellulose paper. However, it bound to all three glycolipids by an immunospot assay on thin layer chromatography (TLC) plates. In studies to determine whether GalS could be a receptor for gp120 on the surface of cells, gp120 bound to GalS incorporated into the plasma membrane of lymphoid cells as determined by cytofluorometric analysis and immunofluorescence microscopy. These studies indicate that GalS may function as a receptor for gp120 and HIV-1.

T-BAM/CD40-L on helper T lymphocytes augments lymphokine-induced B cell Ig isotype switch recombination and rescues B cells from programmed cell death

An important component of T cell help for B lymphocyte differentiation is the contact-dependent signaling mediated by the T cell-B cell activating molecule (T-BAM/CD40-L), an activation-induced surface membrane protein on CD4+ T helper cells in lymphoid follicles that interacts with the B cell surface molecule, CD40. The present study dissects the roles of T-BAM/CD40-L in helper function by means of a neutralizing anti-T-BAM/CD40-L mAb (5c8), a T-BAM/CD40-L-expressing T cell tumor subclone (Jurkat D1.1), and a T-BAM/CD40-L-responsive IgM+ B cell tumor of germinal center origin (RAMOS 266). Like activated T cells, D1.1 cells induce B cells to synthesize IgG, IgA, and IgE in a process that is specifically inhibited by the mAb 5c8. Although rIL-4 alone, but not Jurkat D1.1, induces IgH C gamma mRNA transcripts in RAMOS 266, the T-BAM/CD40-L molecule on D1.1 acts on rIL-4-primed RAMOS B cells to augment expression of C gamma transcripts. In addition, IgG+ RAMOS 266 clones were expanded from D1.1- and rIL-4-stimulated cultures that had undergone deletional IgH isotype switch recombination events. Furthermore, T-BAM/CD40-L signals delivered by the D1.1 clone dramatically rescue RAMOS 266 from mAb anti-IgM-induced apoptosis. Taken together, these data support the idea that T-BAM/CD40-L plays important roles in inducing Ig isotype switch recombination and the clonal selection of isotype-switched B cells.

CD40 molecules induce down-modulation and endocytosis of T cell surface T cell-B cell activating molecule/CD40-L. Potential role in regulating helper effector function

The T-BAM/CD40-L molecule on CD4+ T cells interacts with B cell CD40 molecules to deliver contact-dependent signals that drive B cell activation and Ig secretion. Cell surface T-BAM/CD40-L expression is transient and may be closely regulated in order to limit the activation and clonal selection of noncognate B cells. We demonstrate that B cells, but not non-B cells, rapidly and specifically down-modulate surface T-BAM/CD40-L expression in a contact-dependent and temperature-sensitive manner that renders T cells unable to activate resting bystander B cells. Because the ability to down-modulate T-BAM/CD40-L correlated with CD40 expression, the role of CD40 molecules in down-modulating its ligand was directly assessed. Anti-CD40 mAb, but not control mAb, block B cell-induced T-BAM/CD40-L down-modulation. Furthermore, CD40+ nonlymphoid transfectants specifically down-modulate surface T-BAM/CD40-L expression. B cells induce T-BAM/CD40-L internalization into cytoplasmic compartments in a process that is inhibited by cytochalasin B. Pretreatment of activated T cells with lysosomotropic agents does not affect CD40-induced down-modulation of surface T-BAM/CD40-L but results in a marked accumulation of T-BAM/CD40-L in cytoplasmic vesicles. Together, these studies strongly suggest that CD40 induced T-BAM/CD40-L down-modulation occurs, in part, by receptor-mediated endocytosis followed by lysosomal degradation and may represent a mechanism to regulate CD4+ T cell helper effector functions.

CD40 molecules induce down-modulation and endocytosis of T cell surface T cell-B cell activating molecule/CD40-L. Potential role in regulating helper effector function

The T-BAM/CD40-L molecule on CD4+ T cells interacts with B cell CD40 molecules to deliver contact-dependent signals that drive B cell activation and Ig secretion. Cell surface T-BAM/CD40-L expression is transient and may be closely regulated in order to limit the activation and clonal selection of noncognate B cells. We demonstrate that B cells, but not non-B cells, rapidly and specifically down-modulate surface T-BAM/CD40-L expression in a contact-dependent and temperature-sensitive manner that renders T cells unable to activate resting bystander B cells. Because the ability to down-modulate T-BAM/CD40-L correlated with CD40 expression, the role of CD40 molecules in down-modulating its ligand was directly assessed. Anti-CD40 mAb, but not control mAb, block B cell-induced T-BAM/CD40-L down-modulation. Furthermore, CD40+ nonlymphoid transfectants specifically down-modulate surface T-BAM/CD40-L expression. B cells induce T-BAM/CD40-L internalization into cytoplasmic compartments in a process that is inhibited by cytochalasin B. Pretreatment of activated T cells with lysosomotropic agents does not affect CD40-induced down-modulation of surface T-BAM/CD40-L but results in a marked accumulation of T-BAM/CD40-L in cytoplasmic vesicles. Together, these studies strongly suggest that CD40 induced T-BAM/CD40-L down-modulation occurs, in part, by receptor-mediated endocytosis followed by lysosomal degradation and may represent a mechanism to regulate CD4+ T cell helper effector functions.

The gp120 glycoprotein of human immunodeficiency virus type 1 binds to sensory ganglion neurons

Using immunofluorescence microscopy we found that gp120 binds to the surface of rat dorsal root ganglia neurons and human neuroblastoma cells but not to rat fibroblasts or glial cells. The binding of gp120 to neurons was eliminated by pretreatment with trypsin, which removes cell-surface proteins, but not with chloroform: methanol, which removes glycolipids. As control, neuronal staining by antisulfatide antibodies was eliminated by pretreatment with chloroform: methanol but not with trypsin. The gp120 binding to neurons was also inhibited by the mouse monoclonal antibody 01, which binds to galactocerebroside and cross-reactive glycoproteins. These studies suggest that the receptor for gp120 on the surface of the dorsal root ganglia neurons is a glycoprotein. This interaction may mediate the effects of human immunodeficiency virus type 1 in sensory neuropathy.

Deletions in the ligand for CD40 in X-linked immunoglobulin deficiency with normal or elevated IgM (HIGMX-1)

Patients with X-linked Ig deficiency with normal or elevated IgM (HIGMX-1) fail to switch from IgM/IgD to other Ig isotypes. Interaction between the B cell antigen CD40 and the CD40 ligand expressed on activated T cells is critical for T cell driven isotype switching. We have reported that T lymphocytes from three unrelated male patients with HIGMX-1 failed to express CD40 ligand on their surface, but the mRNA for CD40 ligand was of an apparently normal size and level. Analysis of CD40 ligand cDNA from two of the patients revealed deletions that alter the reading frame. Patient 1 displayed two mutations: a C-->A transversion at nucleotide 590 and the deletion of an adjacent C nucleotide. The second patient had a 58 bp deletion from nucleotides 289-346. Furthermore, neither patient expressed a protein product detectable by the CD40L mAb, 5c8.

Non-antigen signals for B-cell growth and differentiation to antibody secretion

Recently, significant progress had been made in understanding the T-B lymphocyte interactions that control humoral immunity. This review highlights experiments that demonstrate a central role for interactions between T-cell-B-cell-activating molecule (CD40 ligand) expressed on T cells and CD40 on B cells in B-cell activation and immunoglobulin isotype switching, both in vitro and in vivo.

HIV-gp 160-induced T cell-dependent B cell differentiation. Role of T cell-B cell activation molecule and IL-6

The HIV envelope glycoprotein gp160 has been previously demonstrated to induce differentiation of normal B lymphocytes into Ig-secreting cells; the response is T cell-dependent, and T cells pretreated with gp160 can support B cell differentiation. This study investigates the cell surface molecules and cytokines that play a role in the gp160-induced T-B cell interaction. Utilizing CD4+CD45RO+ cloned T cells as the source of helper cells, we observed that physical contact with B cells is essential for the gp160-induced B cell response; no IgG-secretion occurred if T cells were separated from the B cells by culturing them in Transwell chambers. The expression of T cell-B cell activation molecule, a novel surface molecule associated with T cell activation, was moderately increased by gp160, and antibody to T cell-B cell activation molecule abrogated the gp160-mediated Th cell function. Cell surface molecules LFA-1, ICAM-1, HLA-DR, CD28, and B7 were also involved in the T-B cell interaction since mAb to any of these molecules inhibited the gp160-induced B cell differentiation response. gp160 also induced IL-6R and CD23 molecule expression on B cells when added to cultures of T plus B cells; there was CD23 expression only in cells that formed conjugates with T cells. Paraforamaldehyde-fixed, gp160-pretreated T cells failed to elicit IgG responses in B cells, but did induce CD23 and IL-6R up-regulation on B cells. Addition of exogenous IL-6, but not IL-2 or IL-4, restored the IgG secretion. These findings indicate that the T cell dependence for gp160-induced B cell differentiation responses involves two steps: one requires contact-dependent interaction of several cell surface molecules, and the second requires IL-6 secretion.

HIV-gp 160-induced T cell-dependent B cell differentiation. Role of T cell-B cell activation molecule and IL-6

The HIV envelope glycoprotein gp160 has been previously demonstrated to induce differentiation of normal B lymphocytes into Ig-secreting cells; the response is T cell-dependent, and T cells pretreated with gp160 can support B cell differentiation. This study investigates the cell surface molecules and cytokines that play a role in the gp160-induced T-B cell interaction. Utilizing CD4+CD45RO+ cloned T cells as the source of helper cells, we observed that physical contact with B cells is essential for the gp160-induced B cell response; no IgG-secretion occurred if T cells were separated from the B cells by culturing them in Transwell chambers. The expression of T cell-B cell activation molecule, a novel surface molecule associated with T cell activation, was moderately increased by gp160, and antibody to T cell-B cell activation molecule abrogated the gp160-mediated Th cell function. Cell surface molecules LFA-1, ICAM-1, HLA-DR, CD28, and B7 were also involved in the T-B cell interaction since mAb to any of these molecules inhibited the gp160-induced B cell differentiation response. gp160 also induced IL-6R and CD23 molecule expression on B cells when added to cultures of T plus B cells; there was CD23 expression only in cells that formed conjugates with T cells. Paraforamaldehyde-fixed, gp160-pretreated T cells failed to elicit IgG responses in B cells, but did induce CD23 and IL-6R up-regulation on B cells. Addition of exogenous IL-6, but not IL-2 or IL-4, restored the IgG secretion. These findings indicate that the T cell dependence for gp160-induced B cell differentiation responses involves two steps: one requires contact-dependent interaction of several cell surface molecules, and the second requires IL-6 secretion.

Phosphorothioate oligodeoxynucleotides bind to the third variable loop domain (v3) of human immunodeficiency virus type 1 gp120

Although having variability in primary sequence, the v3 loop of gp120 in pathogenic strains of human immunodeficiency virus type-1 (HIV-1) is positively charged and known to interact with sulfated polysaccharides. Because the interaction of sulfated polysaccharides with the v3 loop inhibits HIV infection in vitro, we investigated the interaction of the v3 loop with phosphodiester (PO) and phosphorothioate (PS) oligodeoxynucleotides (oligos). In a solid-phase ELISA assay, a PS 28-mer homopolymer of cytidine, SdC28, blocked the binding of the v3 loop-specific monoclonal antibody (mAb) 9284 to rgp120 more potently than did dextran sulfate. In addition, like dextran sulfate, SdC28 appeared to bind specifically to the v3 loop, because neither compound inhibited the binding of other anti-gp120 mAbs. In contrast to PS oligos, PO oligos did not inhibit mAb 9284 binding. The length dependence of the interaction of PS oligos with the v3 loop was studied by using a series of PS oligos. A discrete loss of inhibiting activity occurred as a function of decreasing PS oligo length, which was most marked between PS oligos of 18-mer and 12-mer in length. We further probed the chemical nature of the interaction of oligos with gp120 by measuring the gp120 binding affinities of PS and PO oligos of various lengths. We employed a 5'-32P-labeled alkylating oligo, ClRNH32P-OdT15, and determined that the Km of gp120 binding is 4 microM. We also determined values of competition constant (Kc) for PS competitors of ClRNH32P-OdT15 binding. The binding constant (= 1/Kc) for PS oligos showed a discrete increase in gp120 binding for PS oligos > 12- to 18-mer in length, with no further increment beyond an 18-mer. Given the important role of the v3 loop in HIV-1 pathogenicity, these data suggest that therapeutic trials of PS oligos should be considered.

Molecular interactions mediating T-B lymphocyte collaboration in human lymphoid follicles. Roles of T cell-B-cell-activating molecule (5c8 antigen) and CD40 in contact-dependent help

In lymphoid follicles, CD4+ T lymphocytes provide contact-dependent stimuli to B cells that are critical for the generation of specific antibody responses in a process termed Th function. The CD4+ T cell-restricted surface activation protein, 5c8 Ag (T-BAM), has recently been shown to be a component of the contact-dependent helper signal to B cells. To further dissect this process, we utilized a Jurkat T cell lymphoma clone, termed D1.1, that constitutively expresses T-BAM and activates peripheral B cells to express surface CD23 in a contact-dependent mechanism that is inhibited by mAb anti-T-BAM (5c8). Similar to its effect on peripheral B cells, Jurkat D1.1 activates B cells from lymphoid organs, as well as a B cell lymphoma clone, RAMOS 266,4CN 3F10 (RAMOS 266), to up-regulate surface CD23. Interestingly, mAb to the B cell surface molecule, CD40 (mAb G28-5 and B-B20), inhibit D1.1 induced activation of RAMOS 266 and peripheral and lymphoid B cells. In contrast, mAb to CR2 or the adhesion molecules, LFA1, LFA3, or ICAM-1, have little effect. The inhibitory effect of anti-CD40 mAb on B cell activation induced by D1.1 is specific because anti-CD40 potentiates, rather than inhibits, the up-regulation of CD23 on B cells induced by rIL-4. Moreover, cross-linking CD40 molecules by anti-CD40 mAb bound to Fc gamma RII+ (CD32) L cells induces B cell CD23 expression. In vivo, T-BAM-expressing cells are CD4+ T cells that are restricted to lymphoid organs and are localized in the mantle and centrocytic zones of lymphoid follicles and the spleen periarteriolar lymphoid sheath in association with CD40+ B cells. Taken together, these data demonstrate that T-BAM on T cells and CD40 on B cells are involved in contact-dependent T-B help interactions that occur in lymphoid follicles.

Molecular interactions mediating T-B lymphocyte collaboration in human lymphoid follicles. Roles of T cell-B-cell-activating molecule (5c8 antigen) and CD40 in contact-dependent help

In lymphoid follicles, CD4+ T lymphocytes provide contact-dependent stimuli to B cells that are critical for the generation of specific antibody responses in a process termed Th function. The CD4+ T cell-restricted surface activation protein, 5c8 Ag (T-BAM), has recently been shown to be a component of the contact-dependent helper signal to B cells. To further dissect this process, we utilized a Jurkat T cell lymphoma clone, termed D1.1, that constitutively expresses T-BAM and activates peripheral B cells to express surface CD23 in a contact-dependent mechanism that is inhibited by mAb anti-T-BAM (5c8). Similar to its effect on peripheral B cells, Jurkat D1.1 activates B cells from lymphoid organs, as well as a B cell lymphoma clone, RAMOS 266,4CN 3F10 (RAMOS 266), to up-regulate surface CD23. Interestingly, mAb to the B cell surface molecule, CD40 (mAb G28-5 and B-B20), inhibit D1.1 induced activation of RAMOS 266 and peripheral and lymphoid B cells. In contrast, mAb to CR2 or the adhesion molecules, LFA1, LFA3, or ICAM-1, have little effect. The inhibitory effect of anti-CD40 mAb on B cell activation induced by D1.1 is specific because anti-CD40 potentiates, rather than inhibits, the up-regulation of CD23 on B cells induced by rIL-4. Moreover, cross-linking CD40 molecules by anti-CD40 mAb bound to Fc gamma RII+ (CD32) L cells induces B cell CD23 expression. In vivo, T-BAM-expressing cells are CD4+ T cells that are restricted to lymphoid organs and are localized in the mantle and centrocytic zones of lymphoid follicles and the spleen periarteriolar lymphoid sheath in association with CD40+ B cells. Taken together, these data demonstrate that T-BAM on T cells and CD40 on B cells are involved in contact-dependent T-B help interactions that occur in lymphoid follicles.

The gp120 glycoprotein of HIV-1 binds to sulfatide and to the myelin associated glycoprotein

We investigated the binding of the gp120 glycoprotein of the human immunodeficiency virus (HIV-1) to neural glycolipids and glycoproteins by ELISA. The gp120 protein bound to sulfatide (GalS), a sulfated glycolipid autoantigen implicated in sensory neuritis, and to the myelin associated glycoprotein (MAG), an autoantigen in demyelinating neuropathy. Binding of gp120 to MAG was inhibited by the HNK-1 antibody, which recognizes a sulfated glucuronic acid epitope, suggesting that the interaction involves carbohydrate determinants. Sulfatide and MAG are potential receptors for gp120 in peripheral nerve and may have a role in the neuropathy associated with HIV-1 infection.