Antibody expression from the core region of the human IgH locus reconstructed in transgenic mice using bacteriophage P1 clones

Mice carrying transgenic human immunoglobulin gene miniloci can be used for the production of human monoclonal antibodies. The human variable region (V) gene segments in these miniloci undergo productive rearrangement in mouse lymphoid tissue to yield a population of B lymphocytes expressing a repertoire of antibodies. Many of the miniloci studied to date have included only a small number of germline gene segments in an artificially compact configuration. Here we describe the use of the bacteriophage P1 cloning system to create mice carrying the core region of the human immunoglobulin heavy chain (IgH) locus. Three P1 clones carrying overlapping regions of the human IgH locus (spanning the five JH-proximal VH segments, the entire DH and JH clusters, and the C mu and C delta constant regions) were injected into mouse eggs and appear to have reconstituted the core region of the locus (> 180 kb) following homologous recombination with each other. While this translocus yielded a titer of serum immunoglobulin similar to that obtained with a smaller plasmid-based minilocus, the P1-based locus gave rise to substantially greater diversification by somatic hypermutation. Such diversification is important for obtaining high-affinity antibodies. The results show the usefulness of the P1 system in facilitating the manipulation and recreation of large transgenes.

Inhibitory effects of fatty acids on glucose-regulated B-cell function: association with increased islet triglyceride stores and altered effect of fatty acid oxidation on glucose metabolism

Long-term exposure to fatty acids (FA) inhibits B-cell function. We tested whether the inhibitory effects are associated with increased islet triglycerides (TG). Rat pancreatic islets were cultured for 48 hours in RPMI 1640 medium with 10% fetal calf serum (FCS) and 11 mmol/L glucose in the presence or absence of the long-chain FA, palmitate. Palmitate (0.125 mmol/L) exposure successively increased islet TG 70% after 6 hours and 200% after 48 hours of culture. The dose-response for palmitate was similar for the increase in TG and inhibition of glucose-induced insulin secretion. Reversal of elevated islet TG in RPMI medium (after 48 hours of palmitate) was 29% after 6 hours and 84% after 24 hours. A more rapid decline of TG was observed in Krebs-Ringer bicarbonate (KRB) medium in the absence of nutrients. This decline was totally prevented by 1 mumol/L of the carnitine palmitoyl transferase-I (CPT-I) inhibitor, etomoxir. Etomoxir enhanced glucose-induced insulin secretion from palmitate-cultured islets; however, this effect was lost when TG were normalized. Under conditions when oxidation of FA from islet TG stores was blocked with etomoxir, we tested the effects of octanoate, the oxidation of which is not blocked by etomoxir. Oxidation of [1-14C]octanoate from islets precultured with palmitate (48 hours) did not differ from that in control islets. Conversely, after palmitate, octanoate inhibited glucose oxidation (14CO2 production from [U-14C]glucose, 613 +/- 41 pmol/10 islets/90 min v 1,129 +/- 87 after control conditions, P < .01). In conclusion, (1) palmitate induces increases in islet TG that are associated with inhibition of B-cell function, and (2) long-term exposure to palmitate also induces an inhibitory effect of FA oxidation on glucose metabolism that is independent of TG.

The T cell leukemia oncoprotein SCL/tal-1 is essential for development of all hematopoietic lineages

The T cell leukemia oncoprotein SCL/tal-1, a basic-helix-loop-helix transcription factor, is required for production of embryonic red blood cells in the mouse yolk sac. To define roles in other lineages, we studied the hematopoietic potential of homozygous mutant SCL/tal-1 -/- embryonic stem cells upon in vitro differentiation and in vivo in chimeric mice. Here we show that in the absence of SCL/tal-1, hematopoiesis, Including the generation of red cells, myeloid cells, megakaryocytes, mast cells, and both T and B lymphoid cells, is undetectable. These findings suggest that SCL/tal-1 functions very early in hematopoietic development, either in specification of ventral mesoderm to a blood cell fate, or in formation or maintenance of immature progenitors.

Molecular cloning of bovine mb-1 cDNA

Ig-alpha of the B-cell antigen receptor complex forms a heterodimeric structure with Ig-beta on the plasma membrane of B-lymphocytes and is apparently involved in signal transduction during the activation of B-cells. Bovine leukemia virus (BLV) is predominantly a B-cell tropic retrovirus, which induces persistent lymphocytosis and leukemia/lymphoma of B-cell lineage in cattle. To understand the mechanisms of proliferation and tumorigenesis of bovine B-cells that are associated with BLV infection, we investigated the B-cell antigen receptor complex, especially bovine mb-1 encoding the bovine Ig-alpha protein. We isolated a full-length bovine mb-1 cDNA clone encoding 223 amino acid residues. The deduced amino acid sequence of the bovine mb-1 showed extensive homology with those of human and murine mb-1. The cytoplasmic tail of the bovine mb-1 also contained a consensus motif (D/E-X7-D/E-X2-L/I-X7-Y-X2-L/I) that may interact with the SH2 domain of src-type kinase. Interestingly, a similar consensus sequence motif was found in the BLV gp30env, although the overall sequence similarity between bovine mb-1 and BLVgp30 was not significant. Furthermore, elevated levels of mb-1 transcript were detected in various bovine leukemia/lymphoma cell lines. These results indicated that the proliferation of B-cells associated with BLV-infection may be related to abnormal signal transduction through the B-cell antigen receptor complex.

Do superantigens play a role in lymphoproliferation?

The T cell superantigens are infectious agents that interact with the T cell receptor and the MHC molecules outside their normal antigen-specific sites, with products of conserved sequences of the variable region chains. This non-specific interaction results in the massive stimulation of T cells (up to 20% of the total) as opposed to conventional antigenic stimulation, which is specific and limited to about 10,000 cells. B cell superantigens have recently been described, stimulating a restricted subset of B cells, those expressing the VH3 subgroup in their rearranged immunoglobulin genes. A number of murine malignancies have been shown to be due to T cell superantigens acting either on T cells or on B cells: the RCS B cell lymphomas in SJL mice, the radiation leukemia virus-induced T cell thymic lymphomas in C57BL/Ka mice and B cell lymphomas in the murine AIDS. We propose that some human B cell malignancies can be due to a similar type of interaction. B cell lymphomas in AIDS patients were recently suggested to be due to the HIV gp120 envelope glycoprotein, a newly recognized superantigen. It can be speculated that the low grade B cell gastric lymphomas of mucosa-associated lymphoid tissue (MALT) are the result of exposure to the H. pylori pathogen. EBV-related lymphocytic proliferation has also been shown to be related with a restricted repertoire and may constitute another example of superantigen driven proliferation. A classification of the various superantigen-driven lymphoproliferative states is proposed.

The Ets protein Spi-B is expressed exclusively in B cells and T cells during development

Spi-B and PU.1 are hematopoietic-specific transcription factors that constitute a subfamily of the Ets family of DNA-binding proteins. Here we show that contrary to previous reports, PU.1 and Spi-B have very different expression patterns. PU.1 is expressed at high levels in B cells, mast cells, megakaryocytes, macrophages, neutrophils, and immature erythroid cells and at lower levels in mature erythrocytes. PU.1 is completely absent from peripheral T cells and most T cell lines based on sensitive RT-PCR assays. In contrast, Spi-B is expressed exclusively in lymphoid cells and can be detected in early fetal thymus and spleen. In situ hybridizations of adult murine tissues demonstrate Spi-B mRNA in the medulla of the thymus, the white pulp of the spleen, and the germinal centers of lymph nodes. Spi-B expression is very abundant in B cells and both Spi-B mRNA and protein are detected in some T cells. In situ hybridization and Northern blot analysis suggest that Spi-B gene expression increases during B cell maturation and decreases during T cell maturation. Gel-retardation experiments show that Spi-B can bind to all putative PU.1 binding sites, but do not reveal any preferred Spi-B binding site. Finally, both PU.1 and Spi-B function as transcriptional activators of the immunoglobulin light-chain enhancer E lambda 2.4 when coexpressed with Pip (PU.1-interaction partner) in NIH-3T3 cells. Taken together, these data suggest that differences in patterns of expression between Spi-B and PU.1 distinguish the function of each protein during development of the immune system.

Immunology: resistance to paratuberculosis

Disease caused by Mycobacterium paratuberculosis involves a complex interaction of lymphoid and phagocytic cells of the peripheral and mucosal immune responses. For resistance to develop, animals must generate an effective cellular immune response to primary infections as well as multifocal exogenous and endogenous reinfections. If an effective immune response does not develop, infected animals transgress through a complex immunologic spectrum in which the immunologic reactions themselves are responsible for the disease manifestations.

Evidence for the release of autocrine growth factor(s) by Hodgkin's cell lines

A cell surface glycoprotein (BLA.36) expressed on Hodgkin's cell and also on normal and malignant B lymphocytes, was identified by reaction with a monoclonal antibody. Expression of BLA.36 was detected on Hodgkin's cell lines, as well as B or pre-B cell lines, but was not detectable on other hematopoietic, carcinoma or melanoma cell lines, both by immunoprecipitation of intrinsically labeled cell lines and by immunocytochemical staining methods. Hodgkin's cell lines which were positive for BLA.36 expression were also responsive to a partially purified Hodgkin's cell growth factor(s) (HCGFs). HCGFs was partially purified by concentrating conditioned medium from a Hodgkin's cell line (HDLM-3), followed by ion-exchange chromatography (DE52) and gel filtration on Sephadex G-50. The active fractions yielded protein bands with apparent molecular weights ranging from 16 to 21 kilodaltons on sodium dodecyl sulphate-polyacrylamide gel electrophoresis under both non-reducing or reducing conditions. Hodgkin's cell lines treated with antiBLA.36 antibody were not growth responsive to exogenously added HCGFs. Addition of alpha-interferon (alpha-IFN) to BLA.36-positive Hodgkin's cell lines resulted in down-regulation of BLA.36, accompanied by inhibition of growth. Cell lines treated in this way failed to respond to exogenously added HCGFs, suggesting a requirement for BLA.36 expression in order for HCGFs to exercise its growth-stimulatory effect.

Differential susceptibility to anti-receptor induced apoptosis in adult murine B-cells: role of B1 cells

We and others have recently found that mature murine B cells can be induced to undergo apoptosis, in vitro, in a dose-dependent manner, by extensive crosslinking of membrane IgM with polyclonal anti-mu. During the analysis of tolerance in transgenic mice expressing rearranged IgM or IgM + IgD receptors, we observed that, Sp6 anti-TNP Ig and anti-MHC transgenic splenocytes, would undergo receptor-mediated apoptosis in vitro just like their normal, non-transgenic littermates. However, transgenic mice expressing rearranged receptors typical of B1 cells, not only contained large numbers of CD5+ cells in their spleens, but these cells failed to undergo apoptosis under conditions that led to programmed cell death in normal splenocytes. B1 spleen cells also failed to proliferate with anti-IgM, although the responsiveness of cells from the other transgenic lines varied depending on the background strains. These differences are due in part, to strain differences, but they also imply that the response pattern of transgenic B cells reflects not only the subset composition in this organ, but also the transgenic specificity of the receptor.

Octamer binding factors and their coactivator can activate the murine PU.1 (spi-1) promoter

PU.1 (spi-1), a member of the Ets transcription factor family, is predominantly expressed in myeloid and B cells, activates many B cell and myeloid genes, and is critical for development of both of these lineages. Our previous studies (Chen, H. M., Ray-Gallet, D., Zhang, P., Hetherington, C. J., Gonzalez, D. A., Zhang, D.-E., Moreau-Gachelin, F., and Tenen, D. G. (1995) Oncogene 11, 1549-1560) demonstrate that the PU.1 promoter directs cell type-specific reporter gene expression in myeloid cell lines, and that PU.1 activates its own promoter in an autoregulatory loop. Here we show that the murine PU.1 promoter is also specifically and highly functional in B cell lines as well. Oct-1 and Oct-2 can bind specifically to a site at base pair -55 in vitro, and this site is specifically protected in B cells in vivo. We also demonstrate that two other sites contribute to promoter activity in B cells; an Sp1 binding site adjacent to the octamer site, and the PU.1 autoregulatory site. Finally, we show that the B cell coactivator OBF-1/Bob1/OCA-B is only expressed in B cells and not in myeloid cells, and that OBF-1/Bob1/OCA-B can transactivate the PU.1 promoter in HeLa and myeloid cells. This B cell restricted coactivator may be responsible for the B cell specific expression of PU.1 mediated by the octamer site.

The proto-oncogene c-maf is responsible for tissue-specific expression of interleukin-4

The molecular basis for the distinctive cytokine expression of CD4+ T helper 1 (Th1) and T helper 2 (Th2) subsets remains elusive. Here, we report that the proto-oncogene c-maf, a basic region/leucine zipper transcription factor, controls tissue-specific expression of IL-4. c-Maf is expressed in Th2 but not Th1 clones and is induced during normal precursor cell differentiation along a Th2 but not Th1 lineage. c-Maf binds to a c-Maf response element (MARE) in the proximal IL-4 promoter adjacent to a site footprinted by extracts from Th2 but not Th1 clones. Ectopic expression of c-Maf transactivates the IL-4 promoter in Th1 cells, B cells, and nonlymphoid cells, a function that maps to the MARE and Th2-specific footprint. Furthermore, c-Maf acts in synergy with the nuclear factor of activated T cells (NF-ATp) to initiate endogeneous IL-4 production by B cells. Manipulation of c-Maf may alter Th subset ratios in human disease.

Late induction of CREB/ATF binding and a concomitant increase in cAMP levels in T and B lymphocytes stimulated via the antigen receptor

Transcription factors of the cAMP-responsive element (CRE) binding protein/activating transcription factor (CREB/ATF) family were implicated in the expression of T cell-specific genes and in the expression of oncogenic retroviruses associated with leukemia in T and B lymphocytes. To study the regulation of CREB/ATF transcription factors during lymphocyte activation, studies were pursued in primary cultures of resting murine splenic T and B lymphocytes stimulated via the Ag receptor. Using consensus/CRE and proliferating cell nuclear Ag (PCNA)/CRE as probes in the DNA binding assay, we showed that a marked induction of CRE binding is associated with activation of splenic T lymphocytes with anti-CD3 Ab. CRE binding was markedly induced after 48 h; it gradually declined at 72 h, but remained elevated above control levels after 120 h. Most significant, activation by anti-CD3 was associated with a marked induction of cAMP levels that preceded the onset of DNA synthesis and the induction of IL-2 secretion and reached a peak after 48 h (9.5- to 11-fold), concomitant with the peak in CRE binding. Rapamycin, a potent immunosuppressant, inhibited the induction of cAMP levels by anti-CD3 concomitant with inhibition of CRE binding activity and arrest of DNA synthesis. A marked induction in CRE binding after 48 h was also found in splenic B lymphocytes stimulated by LPS and anti-Ig and was correlated with a 3- to 4-fold increase in the intracellular levels of cAMP. Two inducible CRE complexes were found to bind to consensus/CRE and PCNA/CRE; the major complex contained primarily CREB homodimers and was constitutively expressed in resting lymphocytes. Conversely, stimulation of lymphocytes was associated with formation of a new, slow migrating CRE complex that demonstrated high inducibility in both consensus/CRE and PCNA/CRE. We show that this de novo inducible CRE complex contains CREB and ATF2, but not ATF1. Taken collectively, these results suggest that recruitment of CREB and ATF2 to the promoter of genes is tightly regulated during activation of T and B lymphocytes and implicate a cross-talk of cAMP and non-cAMP pathways in the regulation of transcriptional processes at late stages of activation in T and B lymphocytes stimulated via the Ag receptor.

Functional reconstitution of oxidase activity in X-linked chronic granulomatous disease by retrovirus-mediated gene transfer

The feasibility of correction of the disease phenotype by gene gene transfer was investigated in cells of four patients with X-linked chronic granulomatous disease. These patients carry point mutations of the gp91-phox gene, encoding for the large subunit of the catalytic core of the phagocytic cell NADPH oxidase. A retroviral vector expressing the gp91-phox protein was constructed and used to transduce lymphoblastoid cell lines established from the patients. Several transduced lymphoblastoid cell clones were investigated for mRNA and protein expression, and for functional reconstitution of oxidase activity. Although extensive quantitative variability was detected among different clones, functional reconstitution of O2- production was obtained in most cases, with oxidase function within the same range as in B cell lines derived from normal individuals. The same vector was also used for transduction of hematopoietic precursors from bone marrow or peripheral blood either with or without enrichment for CD34+ cells. A comprehensive analysis was performed on differentiated myeloid colonies, to evaluate the efficiency of transduction, the levels of gp91-phox expression, and the extent of functional reconstitution of oxidase activity. A high efficiency of transduction was obtained in most experiments, with 60-100% of colonies containing proviral DNA. Among the transduced colonies, an extensive variability in the levels of expression of the transduced gene and of functional restoration of NADPH oxidase activity was observed. These results represent a step toward the development of a gene therapy protocol for these patients.

The B cell coactivator Bob1 shows DNA sequence-dependent complex formation with Oct-1/Oct-2 factors, leading to differential promoter activation

We have shown previously that both octamer binding transcription factors, namely the ubiquitous Oct-1 and the B cell-specific Oct-2A protein, can be enhanced in transcriptional activity by their association with the B cell-specific coactivator protein Bob1, also called OBF-1 or OCA-B. Here we study the structural requirements for ternary complex formation of DNA-Oct-Bob1 and coactivation function of Bob1. In analogy to DNA-bound transcription factors, Bob1 has a modular structure that includes an interaction domain (amino acids 1-65) and a C-terminal domain (amino acids 65-256), both important for transcriptional activation. A mutational analysis has resolved a region of seven amino acids (amino acids 26-32) in the N-terminus of Bob1 that are important for contacting the DNA binding POU domain of Oct-1 or Oct-2. In contrast to the viral coactivator VP16 (vmw65), which interacts with Oct-1 via the POU homeosubdomain, Bob1 association with Oct factors requires residues located in the POU-specific subdomain. Because the same residues are also involved in DNA recognition, we surmised that this association would affect the DNA binding specificity of the Oct-Bob1 complex compared with free Oct factors. While Oct-1 or Oct-2 bind to a large variety of octamer sequences, Bob1 ternary complex formation is indeed highly selective and occurs only in a subset of these sequences, leading to the differential coactivation of octamer-containing promoters. The results uncover a new level in selectivity that furthers our understanding in the regulation of cell type-specific gene expression.

Pattern of T-cell receptor delta gene rearrangement by Southern blotting and polymerase chain reaction technique in Hong Kong Chinese patients with non-T-cell hematological malignancies

It has been recognized that clonal T-cell receptor delta (TCR delta) gene rearrangement is present in both T-and B-cell malignancies. The highly sensitive polymerase chain reaction (PCR) technique may be applicable to cases of leukemia and lymphoma of non-T-cell origin for detection of minimal residual disease (MRD). A PCR technique was used in this study to investigate the pattern of clonal TCR delta gene rearrangement in Hong Kong Chinese patients with non-T-cell hematological malignancies. Seventy-three patients with the diagnosis of acute leukemia and non-Hodgkin's lymphoma of non-T-cell origin were included in this study. There were 20 patients with common ALL (cALL), seven precursal B-cell ALL (PreB-ALL), 23 acute myeloid leukemia (AML), and 23 non-Hodgkin's lymphoma of B-lineage (B-NHL). Clonal rearrangement was detectable by Southern analysis using a J delta 1 probe in 41 per cent of ALL of B-lineage but in none of the B-NHL or AML. The samples were also studied further by monoclonal PCR amplification for TCR delta gene rearrangement. Three different sets of primers were employed to detect clonal rearrangement of the TCR delta gene. The V delta 1(D)J delta 1 recombination typically seen in T-cell malignancies were not seen in any of the of the non-T-cell malignancies. The V delta 2 (D) D delta 3 recombination was found exclusively in ALL of B-lineage and was seen in 73 per cent of the Southern positive cases. Although clonal TCR delta gene rearrangement was undetectable by Southern analysis in our AML cases, 26 per cent had a V delta 2(D)J delta 1 recombination found by the PCR technique. Sensitivity of the PCR technique was determined by serial mixing and was up to 5-10 leukemic cells per 10(4) nucleated cells. It was apparent from this study that it was feasible to detect clonal TCR delta gene rearrangement by the PCR technique in a proportion of the cases of non-T-cell hematological malignancies. The PCR technique can be applied to detect residual leukemic cells in marrow of patients in an apparent morphological complete remission. The value of this application requires further clinical evaluation and correlation.

Widespread clonal B-cell disorder in Sjögren's syndrome predisposing to Helicobacter pylori-related gastric lymphoma

Helicobacter pylori has been identified as a critical antigenic stimulus to the development of gastric lymphoma, but additional factors should be required for such evolution. This topic is now of major importance to clarify the pathobiology of gastric lymphomagenesis. Peculiar autoimmune diseases, such as Sjögren's syndrome, are well known to predispose to B-cell lymphomas. We report on a patient with Sjögren's syndrome and a widespread B-cell lymphoproliferative disorder. A pathological picture of low-grade lymphoma was observed in the stomach, concomitantly with H. pylori infection. However, the B-cell disorder was definitely nonmalignant in the other tissues involved, i.e., the parotid gland and lymph nodes, which are the characteristic targets of Sjögren's syndrome-associated lymphoproliferation. After H. pylori eradication, a dramatic regression of gastric lymphoma into chronic gastritis was observed, but no amelioration occurred in the parotid and nodal involvement. Multiple molecular analyses showed the expansion of the same B-cell clone in synchronous and metachronous lymph node, parotid, and gastric lesions before and after H. pylori eradication. Thus, H. pylori played a crucial role in the local boosting of B-cell lymphoproliferation, but the underlying B-cell disorder was that associated with the autoimmune disease and was nonmalignant. The comprehensive clinical, pathological, and molecular approach allowed us to then distinguish the role of peculiar individual predisposing factors and of local infection in the pathobiology of mucosa-associated lymphoid tissue-associated lymphoproliferation.

Membrane fluidity increases during apoptosis of sheep ileal Peyer's patch B cells

To investigate specific plasma membrane structural changes associated with apoptosis, whole cells and purified plasma membranes of apoptotic B cells from the ileal Peyer's patch of sheep were analyzed for their "membrane fluidity." The ileal Peyer's patch of sheep provided a large number of B cells required for plasma membrane isolation (> 5 x 10(9)). As the incidence of apoptosis increased with time of culture, the fluidity of purified plasma membranes, as measured with the fluorophore DPH (diphenylhexatriene), increased. To evaluate this phenomenon with intact cells, B cells at different apoptotic stages were fractionated on discontinuous Percoll gradients. Similar results were obtained using the fluorophore TMA-DPH (trimethylammoniumdiphenylhexatriene), which has been shown to localize specifically to the plasma membrane. Functionally, the increase in plasma membrane fluidity associated with apoptosis may represent either a mechanism to cycle phosphatidylserine to the outer leaflet, mediating phagocytic recognition of apoptotic cells, or a consequence of this event.

Immune cell proliferation in the harderian gland: an avian model

Experimentation has been carried out to study proliferation of plasma cells in the chicken Harderian gland (HG) and to determine if a HG factor influences immune cell (i.e., B cell) proliferation. In young chickens, flow cytometric analysis of propidium iodide (PI)-stained plasma cells revealed that the percentages of cells in both the synthetic (S) and mitotic (G2M) phases of the cell cycle were highest between 6 and 9 weeks of age. A pattern of plasma cell depletion and repopulation in the HG was observed following administration of emetine dihydrochloride. At 3 and 5 days posttreatment the plasma cell population decreased, and by 7 days posttreatment repopulation of the gland with plasma cells occurred. This repopulation appeared as a result of plasma cell proliferation within the HG. Anti-5-bromo-2'-deoxyuridine (BrdUrd) staining of frozen sections showed that the numbers of plasma cells incorporating BrdUrd were low at 3 days posttreatment but were as high, or higher than, controls at 5 and 7 days posttreatment. These results were verified with flow cytometric data of PI-stained plasma cells. Data from bursal cell bioassays revealed proliferative activity influenced by a HG factor. Coculture of bursal cells with phorbol dibutyrate and diluted HG supernatants resulted in prolonged and increased proliferation of these cells. It is possible that the HG of chickens supports plasma cell proliferation through the elaboration of a factor which acts like a lymphokine.

Involvement of p72syk kinase, p53/56lyn kinase and phosphatidyl inositol-3 kinase in signal transduction via the human B lymphocyte antigen CD22

CD22 is a B lymphocyte-specific membrane protein that functions as an adhesion molecule via its interactions with a subset of alpha 2-6-linked sialic acid-containing glycoproteins. Engagement of CD22 with a monoclonal antibody (HB22.23) that blocks the binding of CD22 to its ligands results in rapid CD22 tyrosine phosphorylation and in increased association of CD22 with p53/56lyn kinase, p85 phosphatidyl inositol-3 kinase, and p72syk kinase. Synthetic peptides that span various regions of the intracellular portion of CD22 were used to map potential kinase binding sites. All three kinases associated with a tyrosine-phosphorylated peptide that spans tyrosine amino acid residues 822 and 842, implicating this as an important region in mediating CD22 signal transduction. In addition, purified p56lyn directly bound to the same peptide. Engagement of CD22 with HB22.23 was sufficient to stimulate normal B cell proliferation. This study further substantiates the importance of CD22 as a B lymphocyte signaling molecule and begins to unravel the mechanisms by which CD22 cross-linking can alter B cell function.

Differential effects of staphylococcal toxic shock syndrome toxin-1 on B cell apoptosis

Superantigens, such as toxic shock syndrome toxin 1 (TSST-1), have been implicated in the pathogenesis of several autoimmune and allergic diseases associated with polyclonal B cell activation. In this report, we studied the in vitro effects of TSST-1 on B cell activation. We show herein that TSST-1 produced antagonistic effects on Ig synthesis by peripheral blood mononuclear cells (PBMC) from normal subjects, depending on the concentration used; Ig production was inhibited at 1000 pg/ml (P < 0.01) and enhanced at 1 and 0.01 pg/ml (P < 0.01) of toxin. Cultures of PBMC were then examined for morphologic features and DNA fragmentation characteristic for apoptosis. B cells exhibited a significantly higher (P < 0.01) incidence of apoptosis after stimulation with 1000 pg/ml of TSST-1 compared with 1 or 0.01 pg/ml of toxin or medium alone. Abundant expression of Fas, a cell surface protein that mediates apoptosis, was detected on B cells after stimulation with 1000 pg/ml of TSST-1 and was significantly higher on B cells undergoing apoptosis than on live cells (P = 0.01). Additionally, increased Fas expression and B cell death occurred at concentrations of TSST-1 inducing the production of high amounts of gamma interferon (IFN-gamma), and both events could be blocked by neutralizing anti-IFN-gamma antibody. These findings suggest that high concentrations of TSST-1 can induce IFN-gamma-dependent B cell apoptosis, whereas at low concentrations it stimulates Ig synthesis by PBMC from normal subjects. These findings support the concept that staphylococcal toxins have a role in B cell hyperactivity in autoimmunity and allergy.

Nonsense mutations inhibit RNA splicing in a cell-free system: recognition of mutant codon is independent of protein synthesis

Mutations resulting in premature termination codons reduce the corresponding mRNA levels. We describe a cell-free system in which depletion of the mutant immunoglobulin kappa mRNA pool correlates with inefficient splicing and not with RNA decay. Splicing deficiency does not depend on the sequence surrounding the in-frame nonsense codon and can be partially corrected by mutating the methionine initiation codon. Despite the apparent link between translation and low mutant mRNA levels, inefficient splicing is not dependent on protein synthesis. Abnormal splicing of mutant immunoglobulin RNA is observed with B-cell but not with HeLa or T-cell extracts. A nonsense mutant beta-globin RNA is normally spliced by B-cell extract. We propose that the phenomenon exhibits tissue and gene specificity.

The mucosa of the middle ear and Eustachian tube in the young rat: number of granulocytes, macrophages, dendritic cells, NK cells and T and B lymphocytes in healthy animals and during otitis media

To gain a better understanding of immune reactions during otitis media, the middle ear and Eustachian tube mucosa were studied as a unit in young rats with respect to the composition of immunocompetent cells before and after middle ear infection via the tube. Using immunohistology, the distribution of NK cells, important for the defence against viral antigens, and of dendritic cells, known to be most capable of antigen uptake, processing and presentation, was determined. Furthermore, the composition of cells of the unspecific immune system (i.e. granulocytes and macrophages) and the specific immune system (i.e. T and B lymphocytes) was studied. Macrophages and dendritic cells were spread over the whole middle ear mucosa, whereas only few NK cells and T and B lymphocytes and almost no granulocytes were detected. In the Eustachian tube mucosa, immunocompetent cells, with the exception of dendritic cells and macrophages, were only rarely seen. After induction of otitis media by severing the soft palate, immunocompetent cells increased in both the middle ear and Eustachian tube mucosa, but surprisingly they were almost absent from the area of the tubal orifice to the middle ear. The results indicate that immune reactions take place similarly in the Eustachian tube and in the middle ear mucosa.

DNA repair activity in protein extracts of fresh human malignant lymphoid cells

Nucleotide excision repair (NER) activity was investigated in lymphocytes from patients with chronic lymphocytic leukemia (CLL). The NER process consists of two broad stages: incision/excision of the damaged oligonucleotide and resynthesis of the repair patch. NER in CLL lymphocytes was monitored with the use of in vitro biochemical assays, allowing the determination of either the extent of repair synthesis or the incision activity on damaged plasmid DNA during incubation with whole-cell protein extracts. Fresh CLL tumor cells were purified from the blood of 7 untreated patients and 11 patients who had been treated with chemotherapy. No repair activity was found in 14 extracts (7 treated and 7 untreated) or in normal blood peripheral lymphocytes. The defect was at the level of both repair synthesis and incision/excision activity of DNA damage. In contrast, 4 of the extracts exhibited 25-60% of the repair activity measured in an extract from a control repair-proficient cell line. A linear relationship was found between the values of DNA-repair synthesis and incision activities, which indicates that the extent of significant incision was the limiting factor in these protein extracts. All of the extracts that exhibited DNA-repair activity were purified from lymphocytes of treated patients. These data suggest that chemotherapy might exert an effect on the status of repair activity in the lymphoid tumor cells of patients.

Immunoglobulins and the regulation of autoimmunity through the immune network

Beneficial effects of the administration of intravenous immunoglobulins (IVIg) have now been reported in a large number of autoimmune diseases, whether mediated by autoantibodies or by autoaggressive T cells. We have proposed that the immunoregulatory effect of IVIg in autoimmune disease is dependent on the selection of the recipient's immune repertoires by the variable (V) region reactivities of infused immunoglobulins. Thus IVIg contains antibodies reactive with idiotypes of natural and disease-related autoantibodies and surface immunoglobulins of B cells; IVIg also contains antibodies reactive with the idiotype, framework and constant regions of the beta chain of the alpha beta T cell receptor. Infusion of IVIg results in transient or long lasting suppression of specific autoantibody clones in vivo and in stimulation of a distinct subset of B cells reactive with the F(ab')2 fragments of IVIg Infusion of IVIg alters the general "architecture" of the network as assessed by studying the kinetic patterns of spontaneous fluctuations of natural autoantibodies in serum. Infusion of normal mouse Ig in healthy adult mice selects expressed immune repertoire by removing late pre-B and B cells in the bone marrow, mostly those expressing D proximal Vh genes, and by activating distinct subsets of B cells and CD4+ T cells in the spleen. Although dependent on the V region reactivities (composition) or injected preparations, these effects probably also require that the infused immunoglobulin contains an intact Fc moiety. If one considers the effect of IVIg on the structure, function and dynamics of the immune network IVIg may be viewed as a substitutive therapy for the quantitative/qualitative defects in network regulation that are associated with autoimmune diseases.