Biomedical subjects

K E Pollok

Publications and source records attributed to K E Pollok.

At least 19 recordsLinked to original sources

PubMed2001

Differential transduction efficiency of SCID-repopulating cells derived from umbilical cord blood and granulocyte colony-stimulating factor-mobilized peripheral blood.

The gene transfer efficiency into nonobese diabetic/severe combined immunodeficient (NOD/SCID)-repopulating cells (SRCs) derived from umbilical cord blood (UCB) (n = 11 NOD/SCID mice) and granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood (MPB) (n = 64 NOD/SCID mice) was compared using a clinically relevant protocol and a retrovirus vector expressing the enhanced green fluorescent protein (EGFP). At 6-9 weeks after transplantation, the frequency of transduced human cells in the bone marrow (BM) (40.5% +/- 2.4% [mean +/- SE]) and spleen (SPL) (36.4% +/- 3.2%) in recipients of UCB cells was significantly higher (p < 0.001) than that observed in the BM (2.2% +/- 1.8%) and SPL (2.0% +/- 2.6%) in recipients of MPB. In subsequent studies, MPB was cultured for 2-8 days in cytokines prior to transduction to determine if longer prestimulation was required for optimal gene transfer. A significant increase in gene transfer into CD45(+) human cells and clonogenic cells derived from MPB SRCs was observed when cells were prestimulated for 6 days compared to 2 days prior to transduction (p = 0.019). However, even after 6 days of prestimulation, transduction was still significantly less than UCB. A substantial discrepancy exists in the ability to introduce genes effectively via retrovirus vectors into SRCs derived from MPB as compared to UCB.

Animals↗

PubMed2001

Interleukin-5 inhibition of biliary cell chloride currents and bile flow.

Recent studies have detected significant elevations of interleukin (IL)-5 mRNA in the liver parenchyma of patients with both primary biliary cirrhosis and acute rejection after liver transplantation. In both of these disorders, intrahepatic biliary epithelial cells (BECs) are the targets of injury. We hypothesized that BECs may themselves express IL-5 receptors that may modulate key biliary functions. RNAs coding for IL-5alpha and -beta receptors were amplified by RT/PCR from a biliary cell line derived from a human cholangiocarcinoma (Mz-ChA-1) and verified by DNA sequencing. IL-5 receptor distribution was detected immunocytochemically on Mz-ChA-1 cells, immortalized murine BEC, bile duct-ligated rat liver, and isolated cholangiocytes. Patch-clamp studies on Mz-ChA-1 cells showed that IL-5 inhibits 5'-N-ethylcarboxamidoadenosine-stimulated chloride currents. Additional functional studies showed that IL-5 inhibits secretin-induced bile flow. We conclude that BECs express IL-5 receptors and that IL-5 modulates BEC chloride currents and fluid secretion. Since IL-5 has previously been associated with cholestatic liver disease, we speculate that IL-5 may contribute to liver injury through its effects on biliary secretion.

Animals↗

PubMed1999

Simultaneous ex vivo expansion of cytomegalovirus and Epstein-Barr virus-specific cytotoxic T lymphocytes using B-lymphoblastoid cell lines expressing cytomegalovirus pp65.

Cytomegalovirus (CMV) infection and Epstein-Barr virus (EBV)-induced lymphoproliferative disease are serious complications associated with allogeneic stem cell transplantation. Immunotherapy using ex vivo expanded, virus-specific cytotoxic T lymphocytes (CTL) has been explored and proven to be effective in therapeutic or prophylactic regimens for CMV and EBV infections. To generate CTL specific for both CMV and EBV, we engineered EBV-transformed B-lymphoblastoid cell lines (BLCL) to express CMV pp65 for use as antigen-presenting cells (APC). BLCL were transduced with a recombinant retrovirus encoding pp65, the immunodominant CMV polypeptide. Western blot analysis and immunocytochemistry confirmed the expression of pp65 in the transduced cells. Peripheral blood mononuclear cells (PBMC) from healthy CMV seropositive donors were stimulated with autologous pp65-expressing BLCL weekly for 3 weeks. Chromium release assays showed that the resulting CTL cultures possessed specific cytotoxicity against EBV and CMV. Recombinant vaccinia viruses encoding individual CMV peptides were used to demonstrate that this CMV-specific cytotoxicity was specific for pp65. Assays on CD4- and CD8-depleted CTL fractions indicated that CD8(+) CTL mediated the pp65-specific cytotoxicity. These CMV/EBV-specific CTL recognized CMV- and EBV-infected targets sharing HLA class I antigens, but not HLA mismatched targets. Our results demonstrate that BLCL can be used as APC to stimulate expansion of EBV- and CMV-specific CTL simultaneously. These findings have potential implications for posttransplant CMV and EBV immunotherapy in recipients of allogeneic stem cell transplants.

Antigens, Viral↗

PubMed1999

Costimulation of transduced T lymphocytes via T cell receptor-CD3 complex and CD28 leads to increased transcription of integrated retrovirus.

Primary human T lymphocytes were transduced at high efficiency with the Moloney murine leukemia virus (Mo-MuLV) vector, LNC-mB7-1, in which an internal cytomegalovirus (CMV) promoter drives expression of the murine B7-1 cDNA. Compared with transduced T cells expanded in IL-2 or reactivated with soluble antibodies to CD3 or CD28, transgene expression was significantly increased after activation on immobilized anti-CD3 antibodies (CD3i) or by simultaneous activation on immobilized anti-CD3 and anti-CD28 antibodies (CD3i/CD28i). A similar pattern of transgene expression was observed in T cells transduced with Mo-MuLV LNC-EGFP. Proviral copy number was maintained in LNC-mB7-1-transduced T cells expanded in IL-2 or reactivated on CD3i/CD28i. Substantial increases in LNC-mB7-1 steady state mRNA in reactivated T lymphocytes, compared with those maintained in IL-2, correlated with increased transcription of the LNC-mB7-1 proviral DNA. Furthermore, T cells transduced with the Mo-MuLV ZIPPGK-mADA, in which the mADA cDNA is driven by an internal human phosphoglycerate kinase (PGK) promoter, showed increases in steady state ZIPPGK-mADA RNA on reactivation. High levels of transgene expression were evident irrespective of cell cycle position in both CD4+ and CD8+ lymphocytes. After reactivation, increases in LNC-mB7-1 mRNA were observed in the presence of the protein synthesis inhibitor cycloheximide, indicating that proteins involved in upregulating transgene expression preexisted in transduced lymphocytes. Induction of transgene expression on CD3i/CD28i showed a dose-dependent decrease in transgene expression when incubated with selective protein kinase inhibitors. These data provide new insights into the mechanisms governing transgene expression driven by Mo-MuLV constructs containing internal promoters in transduced primary T lymphocytes.

Antibodies↗

PubMed1999

CD4(+) Epstein-Barr virus-specific cytotoxic T-lymphocytes from human umbilical cord blood.

Umbilical cord blood (CB) is increasingly used for allogeneic hematopoietic stem cell transplantation. To determine whether viral antigen-specific cytotoxic T-lymphocytes (CTL) could be generated from the predominantly naive T-cell populations in CB, CB-derived mononuclear cells were stimulated with autologous Epstein-Barr virus (EBV) transformed B-lymphoblastoid cell lines over several weeks in the presence of recombinant human interleukin-2 (IL-2). By 28 days of culture, T-lymphocytes from all six CB that had been treated with IL-2 displayed EBV-specific cytotoxicity. These cells were largely CD4(+), with complete inhibition of cytotoxicity by anti-CD3 and variable inhibition by anti-HLA DR monoclonal antibodies. The EBV-specific effectors were cloned by limiting dilution, and most of the CTL clones were CD4(+). The cytotoxicity of the CB-derived CD4(+) CTL clones was inhibited by EGTA but not by anti-Fas ligand mAb, suggesting that this cytotoxicity was mediated by perforin/granzyme B. These data indicate that virus-specific CTL can be cultivated and cloned from CB, a human T-cell source that may not have prior in vivo antigenic exposure or reactivity. This finding may have applications in adoptive immunotherapy to recipients of CB transplants.

Adult↗

PubMed1999

Simultaneous infection with retroviruses pseudotyped with different envelope proteins bypasses viral receptor interference associated with colocalization of gp70 and target cells on fibronectin CH-296.

Several factors are thought to limit the efficiency of retroviral transduction in clinical gene therapy protocols that target hematopoietic stem cells. For example, the level of expression of the amphotropic receptor Pit-2, a phosphate symporter, appears to be low in human and murine hematopoietic stem cells. We have previously demonstrated that transduction of hematopoietic cells in the presence of the fibronectin (FN) fragment CH-296 is extremely efficient (H. Hanenberg, X. L. Xiao, D. Dilloo, K. Hashino, I. Kato, and D. A. Williams, Nat. Med. 2:876-882, 1996). To examine functionally whether the retrovirus receptor is a limiting factor in transduction of hematopoietic cells, we performed competition experiments in the presence of FN CH-296 with retrovirus vectors pseudotyped with the same or a different envelope protein. We demonstrate in both human erythroleukemia (HEL) cells and primary human CD34(+) hematopoietic cells inhibition of efficient infection due to receptor interference when two vectors targeting the amphotropic receptor are used simultaneously. Receptor interference lasted up to 24 h. No interference was demonstrated when vectors targeting the amphotropic receptor and the gibbon ape leukemia virus (GALV) receptor Pit-1 were used concurrently. In contrast, simultaneous infection with vectors targeting both Pit-1 and Pit-2 yielded transduction efficiencies consistently higher than with either vector alone in both HEL cells and human CD34(+) hematopoietic cells. These data demonstrate that the use of FN CH-296 leads to amphotropic receptor saturation in these cells. Simultaneous infection with vectors targeting both amphotropic and GALV receptors may prove to be of additional benefit in the design of gene therapy protocols.

Adult↗

PubMed1999

Facilitation of retrovirus-mediated gene transfer into hematopoietic stem and progenitor cells and peripheral blood T-lymphocytes utilizing recombinant fibronectin fragments.

A transduction strategy has been developed, using fibronectin (FN)-assisted retroviral-mediated gene transfer, based on the observation that hematopoietic stem and progenitor cells bind to specific adhesion domains of fibronectin, via the integrins, very late antigen-4 (VLA-4)alpha 4 beta 1 and very late antigen-5 (VLA-5)alpha 5 beta 1. Retrovirus-mediated transduction on a recombinant FN fragment, FN CH-296, containing binding sites for VLA-4 and VLA-5, separated by type III repeats 12 to 14, makes it possible to efficiently target hematopoietic stem and progenitor cells and T-lymphocytes due to colocalization of target cells and retrovirus particles. These gene therapy strategies are applicable to the potential treatment of a variety of acquired and inherited immune disorders.

Animals↗

PubMed1998

High-efficiency gene transfer into normal and adenosine deaminase-deficient T lymphocytes is mediated by transduction on recombinant fibronectin fragments.

Primary human T lymphocytes are powerful targets for genetic modification, although the use of these targets in human gene therapy protocols has been hampered by low levels of transduction. We have shown previously that significant increases in the transduction of hematopoietic stem and progenitor cells with retroviral vectors can be obtained by the colocalization of the retrovirus and target cells on specific fibronectin (FN) adhesion domains (H. Hanenberg, X. L. Xiao, D. Dilloo, K. Hashino, I. Kato, and D. A. Williams, Nat. Med. 2:876-882, 1996). We studied the transfer of genes into primary T lymphocytes by using FN-assisted retroviral gene transfer. Activated T lymphocytes were infected for three consecutive days on the recombinant FN fragment CH-296 with a retroviral vector encoding the murine B7-1 protein. Transduced lymphocytes were analyzed for murine B7-1 expression, and it was found that under optimal conditions, 80 to 89% of the CD3+ lymphocytes were transduced. Gene transfer was predominantly augmented by the interaction between VLA-4 on the T lymphocytes and the FN adhesion site CS-1. Adenosine deaminase (ADA)-deficient primary T lymphocytes transduced on CH-296 with a retrovirus encoding murine ADA (mADA) exhibited levels of mADA activity severalfold higher than the levels of the endogenous human ADA protein observed in normal human T lymphocytes. Strikingly, the long-term expression of the transgene was dependent on the activation status of the lymphocytes. This approach will have important applications in human gene therapy protocols targeting primary T lymphocytes.

Adenosine Deaminase↗

PubMed1997

Treatment of posttransplant lymphoproliferative disease in the central nervous system of a lung transplant recipient using allogeneic leukocytes.

Posttransplant Epstein-Barr virus-related lymphoproliferative disease (PT-LPD) is a common and often fatal complication following solid organ and hematopoietic stem cell transplantation. PT-LPD following solid organ transplantation generally occurs in B cells of recipient origin in contrast to PT-LPD in marrow transplant recipients, which is exclusively of donor origin. The efficacy of adoptive immunotherapy using donor leukocytes to treat PT-LPD in bone marrow transplant recipients has recently been reported. Because PT-LPD in solid organ transplant recipients is generally of recipient origin, the potential application of adoptive immunotherapy of PT-LPD in solid organ recipients obligates the use of either autologous or allogeneic HLA identical leukocytes, with the attendant risk of organ rejection if cells mismatched with the transplanted organ are used. Nonirradiated allogeneic mononuclear cells from an Epstein-Barr virus (EBV)-seropositive, HLA-identical normal sibling were used to treat a monoclonal EBV lymphoma of recipient origin in the central nervous system of a child who had undergone an HLA-mismatched cadaveric lung transplant. The patient received three separate mononuclear cell infusions over a 9-month period, each containing 1 x 10(6) CD3+ mononuclear cells per kilogram. Complete clinical, radiological, and pathological remission was achieved with this treatment regimen. The response correlated with in vivo reconstitution of normal EBV-specific cytotoxic activity and cytotoxic T lymphocyte precursor frequency. Use of allogeneic HLA-compatible mononuclear cells may thus offer an additional mode of therapy for EBV-related lymphoproliferative disease in selected solid organ transplant recipients refractory to conventional therapies.

Antilymphocyte Serum↗

PubMed1997

Post-transplant EBV induced lymphoproliferative disorders.

Epstein Barr virus induced lymphoproliferative disease (EBV-LPD) is a heterogeneous disorder, ranging from polyclonal lymphoproliferations to malignant lymphoma, typically seen in individuals with inadequate cellular immunity to EBV. The diagnosis of EBV-LPD following transplant requires a high index of suspicion in those patients at risk. Unlike organ transplant patients, in whom lymphomas are generally of host origin and respond to decreases in immunosuppression, bone marrow transplant recipients have donor origin tumors that are not as responsive to conservative treatment modalities. For the latter group, adoptive immunotherapy with donor lymphocytes is the treatment of choice and generally results in complete eradication of these tumors. Whether adoptive immunotherapy can be used for EBV-LPD in patients following organ transplantation is currently being investigated.

Bone Marrow Transplantation↗

PubMed1995

Potential role of 4-1BB in T cell activation. Comparison with the costimulatory molecule CD28.

The expression of the murine T cell Ag 4-1BB, a member of the TNF-R family, is induced by T cell activation. Previously, we and others had shown that signaling through 4-1BB enhanced proliferative T cell responses. To investigate a potential role for the interaction of 4-1BB with its ligand (4-1BBL) in T cell activation, we studied the ability of a soluble chimera of 4-1BB (4-1BBFc) to interfere with proliferative responses and cytokine production in models of activation dependent in intercellular interactions. The potential blocking effect of 4-1BBFc was compared with that of the chimeric molecule CTLA-4Ig, a reagent known to interfere with the interaction of CD28 (and/or CTLA-4) with B7 costimulatory receptors. In this study, we report that 4-1BBFc partially blocked both the activation of unfractionated splenocytes triggered by soluble anti-CD3 (anti-CD3s), and the more physiologically relevant responses to alloantigen. In addition, we show that both chimeric molecules partially blocked proliferative responses and IL-2 secretion by highly purified resting T cells activated with anti-CD3s in the presence of fixed accessory cells that express B7 receptors and 4-1BBL. Furthermore, in this model system, the blocking capacity of 4-1BBFc and CTLA-4Ig appears to correlate with the relative expression of their respective cognate receptors (4-1BBL and B7) on the accessory cell. Simultaneous addition of both blocking reagents produced an additive effect in the model systems studied.

Animals↗

PubMed1995

Role of 4-1BB ligand in costimulation of T lymphocyte growth and its upregulation on M12 B lymphomas by cAMP.

K46J B lymphomas express a T cell costimulatory activity that is not inhibited by CTLA-4Ig, anti-B7-1, anti-B7-2, anti-intercellular adhesion molecule 1 or antibodies to heat stable antigen. In this paper we report that this costimulatory activity is mediated at least in part by 4-1BB ligand, a member of the tumor necrosis factor (TNF) gene family that binds to 4-1BB, a T cell activation antigen with homology to the TNF/nerve growth factor receptor family. A fusion protein between 4-1BB and alkaline phosphatase (4-1BB-AP) blocks T cell activation by K46J lymphomas in both an antigen-specific system and with polyclonally (anti-CD3) activated T cells. 4-1BB-AP also blocks antigen presentation by normal spleen cells. When the antigen-presenting cells express B7 molecules as well as 4-1BB ligand, we find that B7 molecules and 4-1BB-AP both contribute to T cell activation. These data suggest that 4-1BB ligand plays an important role in costimulation of IL-2 production and proliferation by T cells. The B lymphoma M12 expresses low levels of 4-1BB-L but can be induced to express higher levels by treatment of the B cells with cAMP, which also induces B7-1 and B7-2 in these cells. Thus cAMP appears to coordinately induce several costimulatory molecules on B cells.

4-1BB Ligand↗

PubMed1995

Regulation of 4-1BB expression by cell-cell interactions and the cytokines, interleukin-2 and interleukin-4.

4-1BB expression increased gradually following T cell activation, and by day 3 post-stimulation with immobilized anti-CD3 (anti-CD3i) or concanavalin A (Con A), splenic T cells were routinely 35-45% 4-1BB+ by flow cytometric analysis. 4-1BB was expressed on activated CD8+, CD4+, CD28+ and CD45RB+ T cells. Optimal 4-1BB expression was seen by day 6 post-stimulation and was cell density dependent. When T cells were cultured for 6 days at 1 x 10(6)/well in a 24-well plate with anti-CD3i, 82% of the cells were 4-1BB+. In contrast, at lower cell densities (4 x 10(5), 2 x 10(5) and 1 x 10(5)), optimal 4-1BB expression was observed only if the cultures were supplemented with recombinant interleukin-2 (IL-2) or recombinant IL-4 (IL-4). In agreement, with these results, modes of inducing endogenous IL-2 production such as cross-linking the costimulatory molecule, CD28, or the addition of syngeneic accessory cells to T cells activated with anti-CD3i, resulted in high levels of 4-1BB expression. The addition of interleukin-1 alpha (IL-1 alpha) or interferon-gamma (IFN-gamma) did not increase 4-1BB expression on anti-CD3i-activated T cells. In addition, if T cells were incubated with IL-2, IL-4, IL-1 alpha, IFN-gamma or anti-CD28 alone, no 4-1BB expression was induced. T cells activated with soluble anti-CD3 (anti-CD3s) in the presence of IL-2, IL-4, or accessory cells, did not express higher levels of 4-1BB on their cell surface. These data suggest that initial events crucial for efficient T cell activation, such as signals delivered through the T cell receptor/CD3 complex and the CD28 molecule, are instrumental in regulating subsequent 4-1BB expression.

Animals↗

PubMed1995

Characterization of human homologue of 4-1BB and its ligand.

The human homologue of 4-1BB (H4-1BB) cDNA was isolated from PMA plus ionomycin-treated human peripheral T-cell cDNA libraries. The amino acid sequence deduced from the nucleotide sequence showed that the protein is composed of 255 amino acids with 2 potential N-linked glycosylation sites. The molecular weight of its protein backbone is calculated to be 27 kDa. The H4-1BB contains features such as signal sequence and transmembrane domain, indicating that it is a receptor protein. This protein showed 60% identity of amino acid sequence to mouse 4-1BB. In the cytoplasmic domain there are 5 regions of amino acid sequences conserved from mouse to human, indicating that these residues might be important in the 4-1BB function. H4-1BB mRNA was detected in unstimulated peripheral blood T cells and was inducible in T-cell lines such as Jurkat and CEM. H4-1BB-AP, a fusion protein between the H4-1BB extracellular domain and alkaline phosphatase, was used to identify the ligand for the H4-1BB. Although the H4-1BB ligand was detected in both T and B cells of human peripheral blood, the ligand was preferentially expressed in primary B cells and B-cell lines. Daudi, a B-cell lymphoma, was one of the B-cell lines that carried a higher number of ligands. Scatchard analysis showed that the Kd = 1.4 x 10(9) M and the number of ligands in Daudi cell was 4.2 x 10(3).

3T3 Cells↗

PubMed1994

4-1BB T-cell antigen binds to mature B cells and macrophages, and costimulates anti-mu-primed splenic B cells.

4-1BB is expressed on activated murine T cells and may function as an accessory signaling molecule during T-cell activation. To identify putative 4-1BB ligands, a fusion protein consisting of the extracellular domain of 4-1BB fused to human placental alkaline phosphatase (4-1BB-AP) was constructed. Alkaline phosphatase activity could then be used as an indicator of the relative amount of bound 4-1BB. These studies indicated that 4-1BB-AP specifically bound to the surface of various mature B and macrophage cell lines. 4-1BB-AP bound at low levels to T cell lines (non-activated and anti-CD3-activated), pre-B-cell lines, and an immature macrophage cell line. 4-1BB-AP did not bind to a glial tumor cell line, HeLa cells, or COS cells. In addition, 4-1BB-AP bound at higher levels to F(ab')2 anti-mu-activated primary B cells compared to anti-CD3-activated primary T cells. Scatchard analysis indicated that the A20 B cell lymphoma expressed 3680 binding sites per cell with a Kd of 1.86 nM. Affinity cross-linking studies demonstrated that a major cell surface species of 120 kDa bound to 4-1BB-AP; 4-1BB-AP also bound to a minor species of approximately 60 kDa. The addition of paraformaldehyde-fixed SF21 cells expressing recombinant 4-1BB synergized with F(ab')2 anti-mu in inducing splenic B cell proliferation suggesting that 4-1BB may function as a regulator of B cell growth.

Animals↗

PubMed1994

Functional analysis of T-cell antigen 4-1BB in activated intestinal intra-epithelial T lymphocytes.

The 4-1BB antigen has been recently demonstrated to be a 30 kDa inducible T-cell antigen and is expressed on the cell surface of activated splenic T cells and thymocytes. This novel T-cell antigen also associates physically with the T cell-specific protein tyrosine kinase, p56lck. We show here that the inducible T-cell antigen 4-1BB is expressed on activated intestinal intra-epithelial T lymphocytes (IEL). After activation, or in the presence of IL-2, the activated IELs showed higher levels of 4-1BB. Functional studies revealed that the activated IELs triggered with anti-4-1BB monoclonal antibody could enhance the level of IEL cytotoxicity against anti-CD3-secreting hybridoma cells. Cross-linking of anti-4-1BB antibody also enhanced the proliferation of IELs. These results suggest that the inducible antigen 4-1BB has broad biological functions which not only play a role in activated splenic T cells and thymocytes but also in the mucosal immune system.

Animals↗

PubMed1993

Novel T cell antigen 4-1BB associates with the protein tyrosine kinase p56lck1.

4-1BB is a 30-kDa inducible T cell Ag, and is expressed predominantly as a 55-kDa dimer on both CD4+ and CD8+ T lymphocytes. The cytoplasmic tail of 4-1BB contains the sequence Cys-Arg-Cys-Pro, which is similar to the sequence Cys-X-Cys-Pro, which mediates the binding of the CD4 and CD8 molecules to the protein tyrosine kinase p56lck. An anti-4-1BB mAb, 53A2, was used to determine whether 4-1BB may associate with p56lck. The 53A2 mAb specifically recognized 4-1BB on a CD8+ T cell line, CTLL-2, and coimmunoprecipitated a 56-kDa protein along with 4-1BB. Peptide mapping indicated that the 56-kDa phosphoprotein was identical to p56lck. The coimmunoprecipitation of p56lck with 4-1BB also occurred in nonlymphoid cells such as insect (Sf-21) and HeLa cells when the two recombinant proteins were coexpressed. Analysis of mutant p56lck recombinant proteins showed that two cysteine residues critical for p56lck-CD4 (or -CD8) complex formation are also required for the p56lck-4-1BB interaction. These studies establish that 4-1BB physically associates with p56lck.

Amino Acid Sequence↗

PubMed1993

Molecular events in B lymphocyte activation: consequences of signals transduced through MHC class II molecules.

Evidence is presented to demonstrate that murine B lymphocytes receive growth stimulatory signals from their surface class II molecules. Monoclonal anti-Ia antibodies enhanced anti-mu-induced B cell proliferative response. The signals through surface immunoglobulin (Ig) and Ia appeared to act sequentially since preexposure to anti-mu was required to observe anti-Ia-induced increase in B cell proliferation. Anti-Ia antibodies did not increase the number of B cells entering the G1 phase of cell cycle but always enhanced transition from G1 into the S phase in response to stimulation with anti-mu. Analysis of early gene expression revealed that signaling through class II molecules led to an increase in anti-mu-induced expression of c-myc, a proto-oncogene, and of ornithine decarboxylase, a key enzyme in polyamine biosynthesis that has been shown to be intimately related to increased cell proliferation.

Animals↗