Analysis of sequential immunoglobulin E-binding epitope of Japanese cedar pollen allergen (Cry j 2) in humans, monkeys and mice

BACKGROUND

Japanese cedar (Cryptomeria japonica; CJ) pollinosis has been reported to occur naturally in Japanese monkeys (Macaca fuscata) as well as in humans. Most human patients and monkeys with pollinosis have specific IgE for Cry j 2, a major allergen of CJ pollen.

OBJECTIVE

The main purpose of this study was to identify IgE B cell epitopes of Cry j 2 using a synthetic peptide in humans, monkeys and mice.

METHODS

We synthesized 38 overlapping peptides that span the entire length of Cry j 2. We examined the B cell epitopes of Cry j 2 that are recognized by IgE in the sera of human patients and monkeys with pollinosis and immunized mice using synthetic peptides of Cry j 2. We also examined the reaction of Cry j 2-specific mouse monoclonal IgG antibodies to the peptides. Furthermore, we conducted a histamine release assay with leucocytes from a pollinosis patient using human serum albumin (HSA) conjugated with the peptides as a B cell epitope.

RESULTS

We found that 16 of the 20 pollinosis patients who had specific IgE to Cry j 2 also exhibited IgE reaction with some Cry j 2 peptides. Of these 16 patients, 10 exhibited IgE reaction with Cry j 2 peptide no. 13 (121GQCKWVNGREICNDRDRPTA140). Five of the seven monkeys with CJ pollinosis exhibited a reaction with peptide no. 13. Furthermore, IgE in mice immunized with Cry j 2 and two mouse monoclonal IgG antibodies reacted with peptide no. 13. Peptide no. 13-conjugated HSA showed the release of histamine from basophils. Furthermore, to determine the minimum epitope in peptide no. 13, we conducted an enzyme-linked immunosorbent assay inhibition test. The core of the epitope in humans, monkeys and mice was 124KWVNGREI131.

CONCLUSION

We found that 124KWVNGREI131 is an important B cell epitope recognized by IgE in humans, monkeys and mice.

Isotype-specific selection of high affinity memory B cells in nasal-associated lymphoid tissue

Mucosal immunoglobulin (Ig)A dominance has been proposed to be associated with preferential class switch recombination (CSR) to the IgA heavy chain constant region, Calpha. Here, we report that B cell activation in nasal-associated lymphoid tissue (NALT) upon stimulation with the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP) coupled to chicken gamma globulin caused an anti-NP memory response dominated by high affinity IgA antibodies. In the response, however, NP-specific IgG(+) B cells expanded and sustained their number as a major population in germinal centers (GCs), supporting the view that CSR to IgG heavy chain constant region, Cgamma, operated efficiently in NALT. Both IgG(+) and IgA(+) GC B cells accumulated somatic mutations, indicative of affinity maturation to a similar extent, suggesting that both types of cell were equally selected by antigen. Despite the selection in GCs, high affinity NP-specific B cells were barely detected in the IgG memory compartment, whereas such cells dominated the IgA memory compartment. Taken together with the analysis of the V(H) gene clonotype in GC and memory B cells, we propose that NALT is equipped with a unique machinery providing IgA-specific enrichment of high affinity cells into the memory compartment, facilitating immunity with high affinity and noninflammatory secretory antibodies.

The PU.1 and NF-EM5 binding motifs in the Igkappa 3' enhancer are responsible for directing somatic hypermutations to the intrinsic hotspots in the transgenic Vkappa gene

Somatic hypermutation is a key mechanism in generating Ig with higher affinities to antigen, a process known as affinity maturation. Using Igkappa transgenes, the 3' enhancer (kappaE3') has been shown to play an important role in introducing hypermutations. In order to identify the cis-acting elements that regulate hypermutagenesis, we have generated transgenic substrates containing mutations/deletions in the kappaE3' region. Here, we report that base substitutions in the kappaE3', either in the PU.1 or in the NF-EM5 binding motif, not only reduce the mutation rate but also disrupt the directed mutagenesis in the intrinsic hotspots of the Igkappa transgene.

Enhancement of mucosal immune response against HIV-1 Gag by DNA immunization

In order to examine the feasibility of Gag-expression DNA as a potential candidate for HIV vaccine using a mouse model, we injected DNA into mice either intramuscularly or by using a gene gun. Both methods induced a low level of antibody production. However, after booster immunization with p24 protein emulsified with complete Freund's adjuvant via a footpad, we found that only the preceding intramuscular DNA immunization induced an anti-Gag Th1-type (IgG(2a)) antibody response, in addition to the enhancement of a Th2-type (IgG(1)) antibody response. Importantly, when mice were boosted intranasally with p24 and cholera toxin, intramuscular DNA injection was found to enhance both systemic and mucosal Gag-specific immune responses. These results indicate that intramuscular DNA immunization confers the inducibility of memory cells, which circulate around various mucosal tissues. Therefore, intramuscular DNA priming, followed by a mucosal booster immunization, could be considered as a regimen applicable to HIV vaccine.

Confined band gap in an air-bridge type of two-dimensional AlGaAs photonic crystal

The transmittance spectrum for an air-bridge type of AlGaAs photonic crystal (PC) slabs successfully fabricated was measured. It is found that the observed spectrum is consistent with both the theoretical band structure and the calculated one. Moreover, the transmittance due to the modes below the light line is found to be almost 100%, indicating that the guided modes should exist. The respective stop bands are observed in the gamma-M direction for TM-like and TE-like modes, implying that a photonic band gap should exist for the TE-like guided modes. The present PC is very suited for controlling the radiation field.

Fas is required for clonal selection in germinal centers and the subsequent establishment of the memory B cell repertoire

In T cell-dependent immune responses, high-affinity B cells are selected and differentiate into memory cells; however, the mechanism behind this process remains largely unknown. Here, we report that the selection of high-affinity B cells within germinal centers (GCs) is impaired in Fas-deficient lpr mice in the primary response, probably owing to inefficient negative selection. The memory compartment in control mice is mostly established by precursors generated from the early GCs, whereas the lpr defect expands the memory compartment by the increased recruitment of newly generated precursors from the late GCs, resulting in the accumulation of heavily mutated memory B cells at high frequency. These results suggest that Fas is required for clonal selection within GCs and the establishment of the memory B cell repertoire.

Identification of a sequential B-cell epitope on major allergen (Cry j 1) of Japanese cedar (Cryptomeria japonica) pollen in mice

BACKGROUND

Japanese cedar (Cryptomeria japonica; CJ) pollinosis is one of the most common allergic diseases in Japan. B cell epitopes on Cry j 1, a major allergen of CJ pollen, have been analyzed by the specific monoclonal antibodies to Cry j 1, and most of these epitopes may be conformational, but no previous report has addressed the analysis of sequential epitope mapping with synthetic peptides. The main purpose of the present study is to identify IgE and IgG B cell epitopes on Cry j 1 by using a synthetic peptide approach in mice.

METHODS

We synthesized 35 overlapping peptides that cover the entire length of Cry j 1 and examined whether mouse IgE and IgG antibodies produced by immunization with Cry j 1 reacted to the Cry j 1 peptides.

RESULTS AND CONCLUSION

We found that mouse IgE and IgG antibodies reacted strongly to Cry j 1 peptide No. 15 ((141)GVEPVHPQDGDALTLRTATN(160)), though those antibodies did not react with other peptides. IgE and IgG antibody binding to peptide No. 15 was completely inhibited by Cry j 1 and the peptide. To determine the minimum epitope in peptide No. 15, we conducted an ELISA inhibition test. IgE and IgG antibody binding to peptide No. 15 was inhibited by smaller peptides of this peptide. We found the core of the epitope to be (145)VHPQDGDA(152).

Transcriptional regulation of HIV-1 LTR during antigen-dependent activation of primary T cells by dendritic cells

Numerous factors are known to bind human immunodeficiency virus (HIV) long terminal repeat (LTR) and activate viral transcription, but little is known as to how they function in naturally activated T cells and to what extent their binding is relevant to HIV replication in vivo. To characterize the HIV LTR-binding factors responsible for antigen-dependent activation of HIV, we examined replication of LTR mutant viruses in CD4+ T cells activated by different stimuli. NF-kappaB or Sp1 mutant virus replicated well in CD4+ T cells activated by phorbol ester and calcium ionophore. When they were activated by antigen-pulsed dendritic cells, the replication of the Sp1-deleted virus was severely impaired in CD45RA+, but not in CD45RO+ T cell subsets that dominantly produce interleukin-2 (IL-2). Stimulation via CD3/CD28 induced a high level of IL-2 production in both T cell subsets, but Sp1-deleted virus poorly replicated in CD45RA+ subset. The level of NF-kappaB and Sp1-binding factors did not differ between these subsets. Our results suggest that additional cofactors distinct from IL-2-inducing signaling molecules are important for LTR activation during antigen-dependent T cell activation.

Inhibition of immunoglobulin E response to Japanese cedar pollen allergen (Cry j 1) in mice by DNA immunization: different outcomes dependent on the plasmid DNA inoculation method

To develop a new immunotherapy for Japanese cedar (Cryptomeria japonica; CJ) pollinosis, we evaluated the use of DNA immunization by inoculating mice with plasmid DNA encoding Cry j 1 as a CJ pollen major allergen (pCACJ1). Repeated intramuscular (i.m.) inoculation of BALB/c mice with pCACJ1 produced anti-Cry j 1 antibody responses, which were predominately of the immunoglobulin G2a (IgG2a) type. Furthermore, this inoculation suppressed immunoglobulin E (IgE) and IgG1 antibody responses to subsequent alum-precipitated Cry j 1 injections. Splenic T cells isolated from mice inoculated with pCACJ1 i.m. secreted interferon-gamma (IFN-gamma), but not interleukin (IL)-4, in vitro upon stimulation with Cry j 1 as well as with p277-288, a peptide corresponding to the T-cell epitope of Cry j 1. In contrast, inoculation of BALB/c mice with pCACJ1 by gene gun injection caused response predominantly of the IgG1 type, and enhanced production of anti-Cry j 1 IgE antibodies to subsequent alum-precipitated Cry j 1 injections. Splenic T cells isolated from pCACJ1-innoculated mice by gene gun injection secreted both IFN-gamma and IL-4 in vitro, upon stimulation with Cry j 1 as well as with p277-288. These findings suggest that i.m. inoculation with pCACJ1 effectively elicits Cry j 1-specific T helper 1 (Th1)-type immune responses, resulting in inhibition of the IgE response to Cry j 1.

Intermolecular Activation of n-Alkanes by a Trinuclear Ruthenium Pentahydride Complex-Formation of closo-Ruthenacyclopentadiene Complexes

The successive activation of alkane C-H bonds on a trinuclear ruthenium cluster enables cleavage of six C-H bonds and the formation of a closo-ruthenacyclopentadiene complex (the structure of the complex obtained with hexane is shown).

Distinct subcellular localization and substrate specificity of extracellular signal-regulated kinase in B cells upon stimulation with IgM and CD40

We and others previously observed that IgM and CD40 stimulation in murine B cells resulted in activation of extracellular signal-regulated kinase (ERK), a subfamily of mitogen-activated protein kinase. The present study demonstrated that ERK was rapidly phosphorylated and translocated to the nucleus in murine B cells upon stimulation with CD40, whereas it was preferentially localized within the cytosol after stimulation with IgM, suggesting that signaling through CD40 and IgM differentially regulates ERK subcellular localization. Costimulation with CD40 and IgM (CD40/IgM) resulted in subcellular localization of ERK within the cytosol, supporting the notion that stimulation with IgM delivers the signal responsible for inhibition of ERK nuclear transport. Consistent with these observations, IgM and CD40/IgM stimulation resulted in activation of ribosomal S6 kinase, which is a cytoplasmic substrate for ERK, whereas CD40 stimulation had little effect on its activity. Disruption of the microtubule by colchicine in WEHI231 cells resulted in reduction of ERK activity in IgM signaling, but not in CD40 signaling, compatible with the notion that the microtubule network may hold cytoplasmic ERK activity mediated by IgM stimulation. These results support the notion that ERK could mediate different effector functions in B cells upon stimulation with IgM and CD40.

Prf, a novel Ets family protein that binds to the PU.1 binding motif, is specifically expressed in restricted stages of B cell development

During the development of lymphocytes, expression of the Ig genes is strictly regulated in a tissue-specific manner and in a time-ordered fashion. We have previously shown that the PU.1 binding motif in the Igkappa 3' enhancer (kappaE3') and a novel Ets family protein other than PU.1 may be possibly involved in the control of V(kappa)-J(kappa) joining. In the attempt to isolate the novel Ets family protein, we have screened cDNA libraries with the yeast one-hybrid method and identified a new PU.1-related factor, Prf. This novel Ets family protein is shown to interact with the PU.1 binding sequences in various promoters and enhancers, including kappaE3'. It was found that expression of the prf gene is predominant in the B-lineage cells, with the exception of immature B cells. Since Prf does not exhibit functions of transcriptional activity, this novel protein may act as an antagonist against other Ets family proteins, e.g. PU.1 and Spi-B. Possible roles of Prf with respect to the B cell differentiation are discussed.

Targeted disruption of Traf5 gene causes defects in CD40- and CD27-mediated lymphocyte activation

TRAF5 [tumor necrosis factor (TNF) receptor-associated factor 5] is implicated in NF-kappaB and c-Jun NH(2)-terminal kinase/stress-activated protein kinase activation by members of the TNF receptor superfamily, including CD27, CD30, CD40, and lymphotoxin-beta receptor. To investigate the functional role of TRAF5 in vivo, we generated TRAF5-deficient mice by gene targeting. Activation of either NF-kappaB or c-Jun NH(2)-terminal kinase/stress-activated protein kinase by tumor necrosis factor, CD27, and CD40 was not abrogated in traf5(-/-) mice. However, traf5(-/-) B cells showed defects in proliferation and up-regulation of various surface molecules, including CD23, CD54, CD80, CD86, and Fas in response to CD40 stimulation. Moreover, in vitro Ig production of traf5(-/-) B cells stimulated with anti-CD40 plus IL-4 was reduced substantially. CD27-mediated costimulatory signal also was impaired in traf5(-/-) T cells. Collectively, these results demonstrate that TRAF5 is involved in CD40- and CD27-mediated signaling.

Expression of cellular adhesion regulatory molecule in hepatocellular carcinoma

Cellular adhesion regulatory molecule (CMAR) enhances the adhesiveness of cells to collagen and laminin and is considered to be a candidate anti-oncogene. The purpose of the present study was to investigate the relationship between the expression of CMAR and clinical features of hepatocellular carcinoma (HCC). Small amounts of liver tissue were obtained from HCC and non-cancerous portions of the liver in 29 patients and from normal liver in seven patients with metastatic liver tumour by biopsy under ultrasound guidance. RNA was extracted with acid guanidinium thiocyanate-phenol-chloroform. Expression of CMAR was assessed by quantitative PCR using beta-actin as an internal standard. A 4 b.p. insertion polymorphism at nucleotide 241 of the CMAR coding region was then investigated using extracted RNA to assess the relationship between the expression of variant mRNA of CMAR and HCC carcinogenesis. The relative expression of CMAR was significantly reduced in HCC compared with non-cancerous and normal livers and had a relationship with certain clinical background factors. The reduced expression of CMAR was thought to be closely associated with the progression of HCC. However, the 4 b.p. insertion polymorphism pattern of CMAR was the same between HCC and non-cancerous liver in all cases in which it was found. These results suggest that progression of HCC may be predicted based on the relative expression of CMAR.

Fas/FasL interaction is not involved in apoptosis of activated CD4+ T cells upon HIV-1 infection in vitro

In HIV-1-infected individuals, Fas expression and Fas/FasL-mediated apoptosis of mature T cells are known to increase compared with those in normal individuals. To elucidate a relation between acute HIV-1 infection and the regulation of Fas/FasL system upon T-cell activation, resting CD4+ T cells were acutely infected or uninfected with HIV-1 and subsequently activated by phorbol myristate acetate and ionomycin (PMA/IM). Four days after infection, when HIV-1 env gp120 is expressed in more than one half of activated T cells, Fas/FasL expression was analyzed by flow cytometry, and apoptosis-inducing activity of these activated primary CD4+ T cells on Fas+ Jurkat cells was examined. The level of Fas or FasL expression was not altered during acute HIV-1 infection. The enhanced apoptosis-inducing activity upon HIV-1 infection was observed in some individuals, but its activity was not Fas/FasL-mediated. These results indicate that HIV-1 infection is not necessarily associated with either upregulation of Fas/FasL expression or Fas/FasL-mediated apoptosis.

Detection of HIV-Gag p24-specific antibodies in sera and saliva of HIV-1-infected adults and in sera of infants born to HIV-1-infected mothers

Secretory immunoglobulin A (IgA) is known to play an important role in the mucosal defense against a variety of pathogens. Although the role of IgA antibodies during sexual transmission of HIV is not clear, HIV-specific IgA antibodies have been detected in various mucosal secretions of HIV-infected individuals. Using a monoclonal antibody against human IgA, we established an ELISA system to detect anti-HIV p24 IgA antibodies in sera and saliva. We have analyzed the levels of anti-HIV p24 IgG and IgA antibodies in sera and saliva of 107 and 119 adults, respectively, with HIV infection at different clinical stages, and in the sera of 13 infants born to HIV-infected mothers. The level of anti-HIV p24 IgA antibodies was lower in sera and higher in saliva as compared to that of anti-HIV p24 IgG antibodies. Where the percentage of HIV-specific serum antibody-positive cases decreased with disease progression, that of saliva antibody-positive cases increased in AIDS patients. Among the 13 infants born to HIV-infected mothers, 7 infants were HIV-p24-specific serum IgA positive. These sera were negative for anti-HIV p24 secretory IgA, suggesting that some infants develop their own immune responses against HIV infection. Thus, the detection of HIV-specific IgA antibodies, especially in saliva, could be a simple and reliable test for the diagnosis of HIV infection.

Generation of intestinal T cells from progenitors residing in gut cryptopatches

Cryptopatches (CPs) are part of the murine intestinal immune compartment. Cells isolated from CPs of the small intestine that were c-kit positive (c-kit+) but lineage markers negative (Lin-) gave rise to T cell receptor (TCR) alphabeta and TCR gammadelta intestinal intraepithelial T cells after in vivo transfer or tissue engraftment into severe combined immunodeficient mice. In contrast, cells from Peyer's patches and mesenteric lymph nodes, which belong in the same intestinal immune compartment but lack c-kit+Lin- cells, failed to do so. These findings and results of electron microscopic analysis provide evidence of a local intestinal T cell precursor that develops in the CPs.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) stimulates extracellular signal-regulated kinase (ERK) activity in CD40 signaling along a ras-independent pathway

CD40 activates nuclear factor kappa B (NF kappa B) and the mitogen-activated protein kinase (MAPK) subfamily, including extracellular signal-regulated kinase (ERK). The CD40 cytoplasmic tail interacts with tumor necrosis factor receptor-associated factor (TRAF)2, TRAF3, TRAF5, and TRAF6. These TRAF proteins, with the exception of TRAF3, are required for NF kappa B activation. Here we report that transient expression of TRAF6 stimulated both ERK and NF kappa B activity in the 293 cell line. Coexpression of the dominant-negative H-Ras did not affect TRAF6-mediated ERK activity, suggesting that TRAF6 may activate ERK along a Ras-independent pathway. The deletion mutant of TRAF6 lacking the NH2-terminal domain acted as a dominant-negative mutant to suppress ERK activation by full-length CD40 and suppress prominently ERK activation by a deletion mutant of CD40 only containing the binding site for TRAF6 in the cytoplasmic tail (CD40 delta 246). Transient expression of the dominant-negative H-Ras significantly suppressed ERK activation by full-length CD40, but marginally suppressed ERK activation by CD40 delta 246, compatible with the possibility that TRAF6 is a major transducer of ERK activation by CD40 delta 246, whose activity is mediated by a Ras-independent pathway. These results suggest that CD40 activates ERK by both a Ras-dependent pathway and a Ras-independent pathway in which TRAF6 could be involved.

Footprint analysis of the RAG protein recombination signal sequence complex for V(D)J type recombination

We have studied the interaction between recombination signal sequences (RSSs) and protein products of the truncated forms of recombination-activating genes (RAG) by gel mobility shift, DNase I footprinting, and methylation interference assays. Methylation interference with dimethyl sulfate demonstrated that binding was blocked by methylation in the nonamer at the second-position G residue in the bottom strand and at the sixth- and seventh-position A residues in the top strand. DNase I footprinting experiments demonstrated that RAG1 alone, or even a RAG1 homeodomain peptide, gave footprint patterns very similar to those obtained with the RAG1-RAG2 complex. In the heptamer, partial methylation interference was observed at the sixth-position A residue in the bottom strand. In DNase I footprinting, the heptamer region was weakly protected in the bottom strand by RAG1. The effects of RSS mutations on RAG binding were evaluated by DNA footprinting. Comparison of the RAG-RSS footprint data with the published Hin model confirmed the notion that sequence-specific RSS-RAG interaction takes place primarily between the Hin domain of the RAG1 protein and adjacent major and minor grooves of the nonamer DNA.

Efficient virus transmission from dendritic cells to CD4+ T cells in response to antigen depends on close contact through adhesion molecules

Monocyte-derived cultured dendritic cells (DCs) are potent antigen-presenting cells (APCs) and are susceptible to HIV-1Lai infection. Compared to the low level of virus production by HIV-1-infected DCs alone, a level of virus two to three orders of magnitude higher was produced by cocultivation of HIV-1-infected DCs with autologous resting CD4+ T cells in the presence of a nominal antigen. In this coculture system, direct contact of HIV-1-infected DCs with T cells was crucial for efficient virus transmission and subsequent virus production. Blocking of the LFA-1/ICAM-1 or LFA-3/CD2 interaction between these cells substantially reduced virus production, without influence or IL-2 production by activated T cells. In contrast, cell-cell transmission of HIV between non-APCs and activated T cells was not blocked by an antibody against LFA-3. Since a low level of virus production by HIV-infected DCs was upregulated by cross-linking of CD40, it was suggested that not only focal adhesion, but also mutual activation of HIV-infected DCs and T cells through adhesion molecules, may potentiate virus transmission and production and that such activation signals to HIV may be distinct from signals responsible for IL-2 production in activated T cells.

The PU.1 binding site is a cis-element that regulates pro-B/pre-B specificity of Vkappa-Jkappa joining

We have previously shown that the PU.1 binding motif (GAG GAA) in the 3'-enhancer region in the Ig kappa gene is responsible for the negative regulation of tissue (B/T)-specific Vkappa-Jkappa joining. Here we report that the PU.1 binding site also regulates the stage (pro-B/pre-B) specificity of Vkappa-Jkappa joining. In the substrate with base substitutions in the PU.1 binding motif, recombination took place in both pro-B (B220dull/CD43+) and pre-B (B220dull/CD43-) cells. In the transcriptional regulation, the PU.1 motif acts in a positive manner cooperatively with the nuclear factor-EM5 (or PIP) motif (GAAAAC), which is located 2 bp downstream from the PU.1 motif. Interestingly, base substitutions in the nuclear factor EM5 (PIP) motif did not affect the pro-B/pre-B specificity of Vkappa-Jkappa joining. Thus, the PU.1 motif regulates both temporal and tissue-specific rearrangements, while nuclear factor-EM5 is not involved in the regulation of Ig kappa recombination.

The PU.1 binding site is a cis-element that regulates pro-B/pre-B specificity of Vkappa-Jkappa joining

We have previously shown that the PU.1 binding motif (GAG GAA) in the 3'-enhancer region in the Ig kappa gene is responsible for the negative regulation of tissue (B/T)-specific Vkappa-Jkappa joining. Here we report that the PU.1 binding site also regulates the stage (pro-B/pre-B) specificity of Vkappa-Jkappa joining. In the substrate with base substitutions in the PU.1 binding motif, recombination took place in both pro-B (B220dull/CD43+) and pre-B (B220dull/CD43-) cells. In the transcriptional regulation, the PU.1 motif acts in a positive manner cooperatively with the nuclear factor-EM5 (or PIP) motif (GAAAAC), which is located 2 bp downstream from the PU.1 motif. Interestingly, base substitutions in the nuclear factor EM5 (PIP) motif did not affect the pro-B/pre-B specificity of Vkappa-Jkappa joining. Thus, the PU.1 motif regulates both temporal and tissue-specific rearrangements, while nuclear factor-EM5 is not involved in the regulation of Ig kappa recombination.

Mouse germinal center B cells with the xid mutation retain responsiveness to antimouse CD40 antibodies but diminish IL-5 responsiveness

The germinal center (GC) develops in secondary lymphoid tissues in response to thymus-dependent (TD) antigens. To investigate the molecular mechanism of B cell differentiation in GC, we enriched GC B cells from spleen of TD antigen-immunized wild-type and X-linked immunodeficient (XID) mice, and examined the differentiation of GC B cells into antigen-specific IgG1 antibody-forming cells (AFC) in response to anti-CD40 mAb and cytokines. A significant proportion of freshly purified GC B cells expressed receptors for IL-4 and IL-5. Anti-CD40 mAb sustained the viability of GC B cells and IL-4 co-operated with anti-CD40 mAb for further enhancement of the cell viability. Anti-CD40 mAb and IL-4 were essential for inducing differentiation of GC B cells into antigen-specific IgG1-AFC and IL-5 efficiently enhanced their differentiation. GC B cells with the xid mutation responded for proliferation to CD40 ligation to a lesser extent and for the IgG1-AFC response to anti-CD40 mAb together with IL-4, but they showed impaired responsiveness to IL-5, regardless of enhanced expression of IL-5R in response to anti-CD40 mAb and IL-4. These results suggest that anti-CD40 mAb, IL-4 and IL-5 play a critical role in the differentiation of mouse GC B cells. The GC B cells from XID mice show a functional defect with respect to IL-5-mediated differentiation.

Accumulation of somatic hypermutation and antigen-driven selection in rapidly cycling surface Ig+ germinal center (GC) B cells which occupy GC at a high frequency during the primary anti-hapten response in mice

Well-developed germinal centers (GC) contain rapidly dividing surface immunoglobulin-negative (sIg-) B cells (centroblasts), and most of their progeny are sIg+ B cells (centrocytes) in a resting state. It has been predicted that somatic hypermutation occurs in centroblasts, whereas antigen-driven selection takes place in centrocytes. The present analysis indicates that murine GC B cells bearing sIg with specificity for an immunizing antigen are in a rapidly cycling state and increase exponentially in number to occupy spleen GC at high frequency during the 1st week after primary immunization; however, the number of these cells is significantly reduced in the 2nd week of immunization. During that period, these proliferating sIg+ GC B cells accumulate somatic hypermutations with nucleotide exchanges indicative of affinity maturation. These sIg+ GC B cells co-express B7-2, ICAM-1, and LFA-1, and have potent antigen-presenting activity which results in T cell activation in vitro. These observations indicate that the sIg+ GC B cells accumulate somatic hypermutations and undergo antigen-driven selection through proliferation, probably upon activation by T cells. This sIg+ GC B cell population may represent cell cycling centrocytes; however, the possibility that these may represent centroblasts undergoing re-expression of sIg could not be excluded.

CD43 expression in a B cell lymphoma, WEHI 231, reduces susceptibility to G1 arrest and extends survival in culture upon serum depletion

CD43 is a major surface sialoprotein on hemopoietic cells, whose extracellular domain is heavily O-glycosylated. The functional role of CD43 in the hemopoietic system is not fully understood; however, it has been suggested that CD43 may have a role in cell-cell repulsion and in modifying T cell proliferation and activation. CD43 is expressed in immature B cells in the bone marrow, but not by peripheral B cells, except for B-1 B cells and plasma cells. To analyze the biological effect of CD43 in B-lineage cells, we transfected mouse CD43 cDNA into a CD43- B cell lymphoma, WEHI 231, and the growth and survival in culture were compared to those of a parental cell line, human CD8 transfectants, and CD43- revertants established from CD43+ clones. We observed that CD43 expression supported cell growth in culture upon serum reduction, whereas growth of CD43- cell lines was barely detected under this condition. CD43- cell lines accumulated in G1 phase of the cell cycle, and the numbers of viable cells were greatly reduced during culture upon serum depletion, whereas expression of CD43 reduced the susceptibility to G1 arrest and temporarily retarded the apoptotic process, which, in turn, resulted in an increase and maintenance of the number of viable cells in culture. The results suggest that CD43 may have some role in the survival and expansion of B-lineage cells. The biological effect of CD43 was initiated without stimulation by cross-linking and was significantly impaired by replacement of the extracellular domain by the human CD8 extracellular domain. The basis of these regulatory processes is discussed.

Expression of Vpre-B3 (8HS-20) molecules by alternative RNA processing

In pre-B cells, mu chains are expressed in association with "surrogate' L chains encoded by the lambda 5 and Vpre-B1 genes. In addition to their association with lambda 5 and Vpre-B1, mu chains in pre-B cells are associated with the products of the Vpre-B3 gene (formerly designated 8HS-20), which display a distinct association with mu chains and biochemical properties in terms of mol. wt, pI value and glycosylation. However, the mechanism of the generation of Vpre-B3 isoforms has been unknown. The present study indicates that the Vpre-B3 gene transcript underwent alternative RNA processing in normal B cells, in a pre-B cell lymphoma and in a mature B cell lymphoma, WEHI 231, that was transfected with the Vpre-B3 genomic clone. Vpre-B3 isoforms were expressed in a WEHI 231 cell line transfected with the Vpre-B3 genomic clone, comparable in biochemical nature to those expressed in a pre-B cell lymphoma. In contrast, expression of one of the isoforms was missing in a cell line transfected with the Vpre-B3 cDNA clone. These results suggest that Vpre-B3 isoforms with distinct biochemical characteristics are derived from alternatively processed Vpre-B3 mRNA.

Activation of mitogen-activated protein kinases via CD40 is distinct from that stimulated by surface IgM on B cells

CD40 plays critical roles in B cell proliferation and differentiation in response to T cell-dependent antigenic stimulation. It has been suggested that CD40-mediated biological activities are transduced by a CD40 receptor-associated factor, CRAF1 and probably by protein tyrosine kinase Lyn and its substrates, phospholipase C gamma (PLC gamma) and phosphatidylinositol-3 kinase (PI-3 kinase). Here, we describe the novel finding that a mitogen-activated protein kinase (MAPK) extracellular signal-regulated protein kinase (ERK) cascade is involved in CD40 signaling in mouse B cells. Analysis of ERK activities in the B cell lymphoma cell line WEHI 231, which shows an increase in DNA synthesis or arrest of the cell cycle by cross-linking of CD40 or surface IgM (sIgM) cross-linking, respectively, indicated that one of the ERK isoforms, ERK2, was preferentially and rapidly activated after CD40 cross-linking. The CD40-mediated ERK2 activation was comparable to that after sIgM stimulation, although the activity was reduced toward the basal level within several minutes after stimulation. In contrast, ERK1 and ERK2 were activated to a similar extent by sIgM cross-linking, and the activities remained stable for at least 10 min. Furthermore, similar features of differential activation of ERK isoforms were observed in normal resting B cells in CD40 and sIgM signaling. These results suggest divergent regulatory pathways for ERK1 and ERK2 activation, and they support the notion that CD40 signaling may utilize a limited set of elements in the ERK cascade. Co-stimulation of WEHI 231 cells with anti-CD40 mAb rescues the cells from anti-IgM-mediated apoptosis, whereas this co-stimulation resulted in activation of ERK isoforms comparable to that in sIgM stimulation, without a synergistic effect. This result indicates the dominance of ERK activation in sIgM signaling over that of CD40, and it suggests that ERK activation may not be linked to the biological effect that CD40 stimulation in this cell line.

Real-time optical image subtraction and edge enhancement using ferroelectric liquid-crystal devices based on speckle modulation

We carried out real-time optical image subtraction and edge enhancement based on a speckle modulation technique by using ferroelectric liquid-crystal polarization switches and a ferroelectric liquid-crystal spatial light modulator. A ferroelectric liquid-crystal spatial light modulator is employed as a real-time and multiple-exposure optical device, and successful results are obtained from three-exposure images modulated by speckles. Thus, image subtraction and edge enhancement are realized in real time. The whole operation is performed within several milliseconds with modest operating conditions. Because the spatial light modulator has a high resolution of greater than 100 line pairs/mm and can store fine speckle patterns, the image qualities we obtained are quite satisfactory.

Suppression of HIV replication in human monocyte-derived macrophages induced by granulocyte/macrophage colony-stimulating factor

Susceptibility to HIV infection was examined in macrophages differentiated from human monocytes by macrophage colony-stimulating factor (M-CSF) or granulocyte/macrophage colony-stimulating factor (GM-CSF). The replication of macrophage-tropic human immunodeficiency virus type-1 (HIV-1), which was determined by reverse transcriptase (RT) activity, was significantly suppressed in macrophages induced by GM-CSF (GM-type macrophages) but not in those induced by M-CSF (M-type macrophages). Multinucleated giant cells were formed only in M-type macrophages after HIV infection. However, the expression of CD4 molecules on the surface of both types of macrophages was similar and the proviral DNA was detectable in cell lysates of both macrophages, although the amount of proviral DNA in M-type macrophages was higher than that in GM-type macrophages. Many steps have been defined in HIV infection and replication, such as adsorption of HIV to the cell surface, internalization of the viral core into the cytoplasm, uncoating of viral RNA, reverse transcription and integration of proviral DNA into cellular DNA, transcription and translation of proviral DNA, assembly of viral components, and budding of virus particles. Our findings suggested that the suppression of HIV-1 replication in macrophages induced by GM-CSF is mainly due to a disturbance at certain steps of replication after synthesis of the proviral DNA. Thus, the suppression of HIV replication in GM-type macrophages may provide a model of the latency of HIV infection in vivo.

Monocyte-derived cultured dendritic cells are susceptible to human immunodeficiency virus infection and transmit virus to resting T cells in the process of nominal antigen presentation

The susceptibility of monocyte-derived cultured dendritic cells (DCs) to human immunodeficiency virus (HIV) infection and their role in viral transmission in the immune response were studied in detail. We observed that highly purified cultured DCs were infected with the T-tropic Lai strain of HIV type 1 (HIV-1Lai) via the CD4 receptor, and this was followed by formation of the complete provirus as detected by PCR. HIV mRNAs were transcribed at only low levels, and virus production was undectable; however, the addition of the purified protein derivative antigen of tuberculin and of autologous resting T cells to HIV-1Lai-infected DCs but not to HIV-1Lai-infected macrophages led to massive HIV transmission and production. These data suggest that the interaction of infected DCs with T cells during the normal immune response could play an important role in the activation and expansion of HIV.

Molecular components and assembly of mu.surrogate light chain complexes in pre-B cell lines

We describe the molecular components, subunit assembly, and cell surface expression of mu-chain complexes in mu+kappa- pre-B cell lines as revealed by two-dimensional gel electrophoresis. The mu-chain complexes of these cell lines contain several previously unreported components, p42(6.4), p39(6.7), p18(8.6), and p14(7.0), in addition to lambda 5, VpreB1, VpreB3 (formerly named 8HS20), MB-1(Ig-alpha), and B29(Ig-beta). These new components are not detected in mu+kappa+ immature B cell lines. The mu-chain associates with lambda 5, VpreB3, and p56(5.0) at an early phase of assembly, preceding the association of other molecules. mu-Associated VpreB3 decreased during assembly as the association of VpreB1 became dominant, suggesting that the change in the ratio of these two VL-like surrogate light chains is involved in the mechanism of assembly. Lambda 5, VpreB1, p56(5.0), p32(5.0), p36(5.5), and p14(7.0) were shown to be expressed on the cell surface in association with mu-chain. The association of the other molecules with mu-chain is most likely restricted to the intracellular compartment. An interaction between VpreB1 and VpreB3 was also suggested. These findings might be important for understanding the function of mu-chain complexes in pre-B cells. A possible signaling mechanism of mu/surrogate light chain complexes is discussed.

Real-time velocity measurement by the use of a speckle-pattern correlation system that incorporates a ferroelectric liquid-crystal spatial light modulator

We describe a technique for noncontact velocity measurement by using double-exposure speckle-pattern techniques with optical signal processing. The two speckle patterns are recorded on a ferroelectric liquid-crystal (FLC) spatial light modulator (SLM), which is a bistable optically addressed SLM, and the composite pattern is then analyzed by an optical system similar to a joint transform correlator, in which another FLC-SLM and a position-sensitive detector are used. We show that the performance of the system can be significantly improved by adjusting the time between exposures using a real-time feedback system that is based on the position of the correlation spot in the output plane.

Analysis of function of a human antigen-presenting cell by xenogeneic interaction with mouse T cells

A human B cell line, ARH, was transfected with a murine major histocompatibility complex class II gene (I-A(k)). One of the transfectants, ARH5.5, which strongly expresses I-A(k) molecules was found to be capable of presenting soluble antigens to I-A(k)-restricted, antigen-specific murine helper T cell (Th) clones. When ARH5.5 was treated with either chloroquine or paraformaldehyde prior to the antigen pulse, it failed to present a protein antigen, ovalbumin, but retained the ability to present a peptide, indicating that the presentation was dependent on processing. The xenogeneic interaction of co-stimulatory molecules on the human antigen presenting cell (APC) and the murine Th cell was assessed by using antibodies against adhesion molecules. We found that the xenogeneic interaction of LFA-1/ICAM-1 acted as a strong co-stimulator of the antigen presentation by ARH5.5, while that of CD2/LFA-3 had only little stimulatory effect. These results suggest that the interaction between some of the adhesion molecules on APC and Th can cross the species barrier. The experimental system presented here is simple and useful for analyzing human APC function, separately from T cell function, especially when the dysfunction of APC associated with viral infection with human tropism is considered.

The fetal thymus stores immature hemopoietic cells capable of differentiating into non-T lineage cells constituting the thymus stromal element

Immature hemopoietic cell lines were established by transforming fetal thymocytes in vitro with a ts mutant of Abelson murine leukemia virus. They are positive for c-kit and IL-2R alpha but negative for lineage specific markers. Their TCR and Ig heavy chain genes are in germline configuration, and are expressed as germline gene transcripts. When these cell lines were stimulated in vitro with IL-1 their morphology changed into that of typical macrophages (M phi). Subsequent analysis of a particular clone, which displayed the morphological change at the highest efficiency among established cell lines, indicated that the clone possesses the capacity to differentiate into I-A-M phi capable of secreting several cytokines, and supporting the proliferation of fetal and adult thymocytes in vitro. If their surface markers are considered, their normal counterparts would be present in a minor subset of CD4-CD8- double-negative cells in the thymus in early development. The results raise the possibility that the thymic organ at an early stage of development stores immature hemopoietic cells capable of differentiating into a non-T lineage constituting the thymic stromal elements.

Characteristics of IgA antibodies against HIV-1 in sera and saliva from HIV-seropositive individuals in different clinical stages

IgA antibodies were analysed in sera and saliva from 40 HIV-1 seropositive individuals. The level of total IgA in serum was elevated according to the progress of the disease. IgA antibodies against p24 and gp160 were detected in the asymptomatic phase of infection. However, they declined in the symptomatic phases in contrast with IgG antibodies. Interestingly, three patients in the symptomatic phase who showed high levels of IgA antibodies were all in relatively good clinical condition. The IgG and IgA antibodies in saliva declined in the symptomatic phase. The level of IgG anti-p24 antibodies in saliva correlated with that in serum, suggesting that IgG anti-p24 antibodies in saliva originated from those in the serum. These results indicate that IgA antibodies are regulated independently from IgG antibodies and that the mucosal immune system is impaired early in the symptomatic phase of HIV infection, which starts with mucosal impairment. Detection of IgA antibodies may be useful for prognosis of the disease in HIV-infected individuals. The results indicate also that treatment for the impaired IgA mucosal immune system should be taken into consideration.

A novel gene product associated with mu chains in immature B cells

A previously unreported B cell specific gene, which we have named 8HS-20, was isolated from the cDNA library of a pre-B cell clone by subtraction and differential hybridization. This gene is selectively expressed as a 0.75 kb transcript in pre-B and bone marrow-derived B cell lines; a transcript of the same size is also found in bone marrow and, albeit at low levels, in spleen. The deduced amino acid sequence of the 8HS-20 cDNA displayed homology to a B cell specific gene, VpreB-1, and to members of the immunoglobulin supergene family including V lambda, V kappa, VH, TCRV alpha, V beta and CD8. Biochemical analysis using purified antiserum against 8HS-20 oligopeptides indicates that the gene encodes proteins with mol. wts of 13.5, 14, 15.5 and 16 kDa, which associate with mu chains in pre-B cell lines, and that these molecules are expressed concomitantly with VpreB-1 and lambda 5 gene products in the same cell lines.

Factors affecting tensile bond strength of composite to dentin

Five factors which might affect the tensile bond strength of an experimental dentin bonding system to extracted human dentin were evaluated. Flat dentin surfaces of extracted human teeth were cleaned with 0.5 mol/L EDTA and pretreated with 35% glyceryl methacrylate solution. A commercial light-activated composite was then bonded using a commercial bonding agent. The five evaluated factors were: 1) embedding or not embedding the specimens in an epoxy resin, 2) thickness of the specimens, 3) crosshead speed during measurement, 4) storage time of the specimens, and 5) dentin substrate depth. Measurements were made of the bond strengths that resulted from the effects of these varied factors. These measurements were compared to a control group. Only the specimen thickness significantly affected the measured bond strength, and extremely thin specimens (about 1 mm) showed the lowest bond strength.

Constitutive expression of the nef gene suppresses human immunodeficiency virus type 1 (HIV-1) replication in monocytic cell lines

In order to study the effect of nef gene expression on viral replication in monocytic cells, we established monocytic (U937 and THP-1) cell transfectants constitutively expressing the human immunodeficiency virus type 1 nef gene. We constructed a plasmid expressing the nef gene derived from an infectious clone, NL432, under the control of SR alpha promoter which can drive a high level of gene expression. We found suppressed viral replication in nef-expressing monocytic cells, although a negative effect of nef was observed, with some variation depending on the virus strain and the cell. We also observed that the expression of the surface CD4 molecule is inversely related to the expression of the nef gene, especially in the U937 transfectants. These results indicate that the suppression of viral replication and the down-modulation of CD4 molecule by nef gene expression occur in monocytic cell lines as in T cell lines.

Heavy chain variable (VH) region diversity generated by VH gene replacement in the progeny of a single precursor cell transformed with a temperature-sensitive mutant of Abelson murine leukemia virus

Sequence analysis of a large number of DNA clones containing a functional heavy chain variable, diversity, and joining (VHDJH) complex generated by VH to VHDJH joining (VH gene replacement) in the progeny derived from a common precursor cell transformed with a temperature-sensitive (ts) Abelson murine leukemia virus (A-MuLV) indicates that endogenous VH gene replacement in vitro generates immunoglobulin gene joints distinct from those generated by the usual VH to DJH joining. Such joints keep the pentamer CAAGA at the 3' end of the donor VH segment and lack a recognizable D segment, as can be seen also in vivo. The results suggest that VH gene replacement participates in generating VH region diversity in vivo, as previously postulated. During the joining process, a unique VH gene was selected in all progeny cells, together with a single A nucleotide dominantly added to the junctional boundaries. The basis of these regulatory processes is discussed.

Characterization of a new subgroup of human Ig V lambda cDNA clone and its expression

From a human bone marrow cDNA library, we have cloned and sequenced a gene which cross-hybridized with murine pre-B cell-specific gene 8HS-20 cDNA under the low-stringent condition. Sequence analysis predicted that this gene (YM-1) encoded 240 amino acids which had the basic structure of immunoglobulin lambda light chain. The 3' half of the YM-1 sequence was identical to the J lambda 2 C lambda 2 region except for four nucleotides. The 5' part of the gene had 87.6% sequence homology with the reported V lambda gene called T1. Comparison of the deduced amino acid sequences with representative members of the seven other V lambda subgroups showed considerable structural homology, but the maximum homology with these chains was 44%. Therefore, we conclude that YM-1 belongs to a new V lambda subgroup. Interestingly YM-1 showed higher homology with VpreB1 (56%) than with any of the other V lambda subgroups. By Southern blot analysis four to six cross-hybridizing V lambda bands were detected at high stringency. Expression of the V lambda gene was observed in immature as well as mature B cell lines without accompanying V-JC gene joining, suggesting that V lambda of the YM-1 locus is activated at the early stage of maturation.

Immunoglobulin V gene replacement is caused by the intramolecular DNA deletion mechanism

Circular DNA resulting from V gene replacement was studied with an A-MuLV transformed cell line containing ablts. This cell line undergoes V gene replacement at elevated temperatures in the immunoglobulin (Ig) heavy chain (H) gene. Examination of circular DNA revealed that a heptamer-related sequence (TACTGTG) within the coding region of VDJ was joined to the recombination signal sequence (RSS) of a germline VH segment. This provides direct evidence for a intramolecular DNA deletion mechanism for V gene replacement. In the pre-B cell line as well as in in vivo lymphocytes, unusual circular DNAs were found which were structurally similar to the V gene replacement circles. They represented excision products of the deletion type recombination between one complete RSS and a heptamer-like sequence in the Ig H region.

[A community-based education program for serum cholesterol reduction in urban hypercholesterolemic persons--comparison of intensive and usual education groups]

A community-based education program was conducted for persons found to be hypercholesterolemic by screening during cardiovascular surveys, in an urban population, to evaluate the feasibility and effect of the program in primary prevention of coronary heart disease. The subjects were men and women aged 40-64 living in the suburbs of Osaka whose serum total cholesterol was between 240 and 299 mg/dl in both the 1988 and the 1989 surveys. Persons with hypothyroidism, those taking medication for hypercholesterolemia or hypertension, and with a history of stroke and coronary heart disease were excluded. Of the 111 persons who were eligible, 104 persons were recruited for the program on March, 1989. The 104 persons were randomly assigned to either an intensive education group (n = 51) or a usual education group (n = 53). For the intensive education group, seven education classes were held from April to November, 1989. Lectures, practice sessions, interviews, and spot cholesterol measurements were conducted in a local community center. The usual education group received a letter with results from the 1989 survey and dietary instruction in April 1989 and an education class in September 1989. Mean serum cholesterol in the intensive education group showed a 10.0 mg/dl greater reduction in September 1989 and a 9.0 mg/dl greater reduction in March 1990 than in the usual education group (p less than 0.05) while mean HDL-cholesterol did not change in either groups. The intensive education group reported a larger decrease in the dietary frequency of chicken egg, poultry skin and small fishes, foods which are rich in saturated fat and cholesterol. The frequency of fatty meat, butter and fish eggs was low in both groups and did not differ between the two groups after the one-year program. These results indicate that a population-based education program is feasible and effective in reducing serum total cholesterol of hypercholesterolemic persons.

Two types of mu chain complexes are expressed during differentiation from pre-B to mature B cells

Immunoglobulin mu chains synthesized in murine pre-B cells are known to be associated with surrogate light chains designated as omega (omega), iota (iota) and B34. In addition to these molecules, we identified the complexes of polypeptides (50, 40, 27 and 15.5 kd) associated with surface or intracellular mu chains of pre-B cell lines. Most of these polypeptides were continuously synthesized and associated with mu chains in virgin B cells lines, although some of them scarcely bound to the mu kappa dimer or mu 2 kappa 2 tetramer concomitantly present in the same clone or population. However, in mature B cells they were no longer detectable except B34. Cross-linking of micron chains on the surface of pre-B cells resulted in an increase in intracellular free Ca2+, indicating that the micron chain complex on the surface of pre-B cell lines acted as a signal transduction molecule. However, the receptor cross-linkage of pre-B cell lines did not induce the increased inositol phospholipid metabolism usually observed in virgin and mature B cell lines. These results suggest that, during the differentiation from pre-B to mature B cells, the cells express two types of mu chain complexes which exhibit different structures as a whole and possess different signal transducing capacities.

B cell precursors are present in the thymus during early development

An in vitro system for transforming immature lymphoid cells present in the thymus at early development has been established. By phenotype analysis of the transformants obtained, we observed that B cell precursors, susceptible to Abelson murine leukemia virus (A-MuLV)- or Harvey murine sarcoma virus (H-MuSV)-induced lymphogenesis, were present at high frequency in the fetal thymus of BALB/c mice. These precursors recolonized alymphoid thymus lobes in vitro, as do T cell precursors. It was further observed that B precursors in the fetal liver were also capable of recolonizing alymphoid thymus lobes and were stored in a thymic environment. These results suggest that stroma cells of the fetal thymus may possess the capacity to support the growth of B precursors. On the other hand, B cell precursors sensitive to the viral transformation were undetectable in the fetal thymus of C57BL/6, although immunohistochemical analysis suggested their presence. However, in the fetal liver of the same strain, B precursors recolonizing alymphoid thymus in vitro were sensitive to the viral transformation. Based on these results, we will discuss both the role and fate of thymic B precursors. In addition, we also obtained T cell lymphomas at different stages of differentiation from the fetal thymus of C57BL/6 infected with A-MuLV or H-MuSV. These data indicate the usefulness of our system in establishing cell lines derived from intrathymic lymphogenesis at early development.

The analysis of immature lymphoid precursors stored in longterm bone marrow culture

The long-term bone marrow culture system developed by Dexter (MBMC) is known to store immature lymphoid precursors capable of differentiating into mature B cells in irradiated or immunodeficient mice. It has been suggested that pre-B cells are not generated under such culture conditions, but that opinion was not based on any systematic analyses. In the present study under carefully controlled conditions, we observed that pre-B and pro-B cells were eliminated from the late stage of primary MBMC, and the former were not generated in recharged MBMC. Under appropriate conditions, these immature precursors in recharged MBMC generated in vitro immunoglobulin-positive (Ig+) cells to differentiate into antibody-forming cells upon stimulation with lipopolysaccharide (LPS). LPS-reactive B cells were observed in every 10th of the Ig+ cells, the frequency being essentially the same as that observed in normal B cells in different tissues. The immature B cell precursors generating LPS reactive cells were expressed in recharged MBMC at the frequency of 4.2 x 10(-6). A staining experiment showed that cells bearing AA4.1 were stored at the frequency of 10(-4)-10(-5). This frequency is thought to be similar to that of lymphoid precursors in recharged MBMC committed to differentiate along B lineage cells. Based on these results, we discussed the stage, nature, and mode of differentiation of immature lymphoid precursors stored in MBMC.

A temperature-sensitive mutant of Abelson murine leukemia virus confers inducibility of IgM expression to transformed lymphoid cells

Lymphoid cell lines were isolated that were inducible for the expression of surface immunoglobulin by shift from 35.5 to 39.5 degrees C after infection of mouse bone marrow cells with a mutagen-treated Abelson murine leukemia virus. Virus produced by one of the cell lines (ts49) transmitted the temperature-sensitive phenotype to new lymphoid transformants as well as to NIH/3T3 cells. In addition, the tyrosine autophosphorylating activity of the p120gag-abl protein synthesized in ts49-transformed cells was found to be temperature-sensitive. Shift experiments using ts49-transformed lymphoid cells showed that at 39.5 degrees C they synthesize increased amounts of mu and kappa chain RNA and protein, and that they can be further induced to secrete IgM when treated with lipopolysaccharide.