Diagnostic usefulness of bone marrow aspiration material for the amplification of IS6110 insertion element in extrapulmonary tuberculosis: comparison of two PCR techniques

SETTING

In many cases of extra-pulmonary tuberculosis (EPTB), with the exception of paucibacillary analysed specimens, the suspected site of mycobacterial infection is relatively inaccessible or unknown, making laboratory confirmation of TB laborious and problematic.

OBJECTIVE

Two different polymerase chain reaction (PCR) based methods were compared to investigate the validity of bone marrow aspiration material as an easily accessible alternative sample for molecular analysis in EPTB.

DESIGN

We amplified the same sequence of IS6110 of Mycobacterium tuberculosis complex in 19 confirmed cases of EPTB using two different nested PCR techniques: one in-house 'classic' PCR and another based on LightCycler technology.

RESULTS

Both methods demonstrated the same reliability when performed in samples of infected tissue. However, the LightCycler protocol was superior to the in-house system when applied in bone marrow aspiration material, revealing positivity in 18/19 compared to 13/19 samples of 'classic' PCR.

CONCLUSION

The application of an optimised LightCycler nested amplification protocol in bone marrow aspirates may promote diagnostic accuracy in difficult and/or urgent cases of EPTB.

Analysis of Btk mutations in patients with X-linked agammaglobulinaemia (XLA) and determination of carrier status in normal female relatives: a nationwide study of Btk deficiency in Greece

Bruton's tyrosine kinase (Btk) is a nonreceptor tyrosine kinase, critical for B-cell development and function. Mutations that inactivate this kinase were found in families with X-linked agammaglobulinaemia (XLA). In this study the Btk gene was analyzed in 13 registered Greek patients with XLA phenotype originated from 12 unrelated families, in order to provide a definite diagnosis of the XLA. The structure of Btk was analyzed at the cDNA level using the recently developed method, NIRCA (Non-Isotopic-Rnase-Cleavage-Assay). Alterations were detected in all patients and sequencing analysis confirmed the results and defined six novel XLA-associated Btk mutations (three missense mutations: C337G, L346R, L452P; one nonsense mutation: Y392X, and two frameshift alterations: c1211-1212delA, c1306-1307insA). Having defined the genetic alteration in the affected males of these families, the information was used to design polymerase chain reaction (PCR) primers and the Btk segments containing the mutated sequences were amplified from peripheral blood derived genomic DNA of potential female carriers. The PCR products were directly sequenced and carrier status was determined in 12 out of 16 phenotypically normal females analyzed. This protocol can be used once the nature of the Btk mutation has been defined in one of the affected males and provides a convenient, simple and reliable way to determine the carrier status of other female family members. Molecular genetic analysis constitutes a determinative tool for the definitive diagnosis of XLA and may allow accurate carrier and prenatal diagnosis for genetic counselling.

Rapid mutational analysis of N-ras proto-oncogene in hematologic malignancies: study of 77 Greek patient

BACKGROUND AND OBJECTIVES

N-ras mutations are the most commonly detected molecular abnormalities in hematologic malignancies, especially in those of myeloid origin. Different techniques have been used to detect N-ras mutations; however, most of them are either labor intensive or provide sequence data for only a limited number of codons. Consequently, study of the N-ras oncogene has not been convenient in every day clinical practice being restricted, as a rule, to retrospective analysis of patients.

DESIGN AND METHODS

In this study we used a recently developed method that enables rapid and reliable detection of mutations at the cDNA level, namely, the non-isotopic RNase cleavage assay (NIRCA). Using this method we were able to screen the N-ras oncogene rapidly and determine the incidence and prognostic significance of N-ras mutations in 77 Greek patients with acute leukemia, myelodysplastic syndromes and chronic myeloproliferative disorders, both at the presentation and during relapse or progression of the disease.

RESULTS

Activating N-ras mutations were detected in 7 patients and our results were confirmed by direct sequencing. Interestingly, two novel alterations were identified, a mutation at codon 8 (characterized by a substitution of valine by leucine) in a patient with chronic myeloid leukemia during hematologic relapse of the disease and a polymorphism at codon 92 (1002T-->C, without amino acid substitution) in a patient with chronic myelomonocytic leukemia.

INTERPRETATION AND CONCLUSIONS

A rapid and easy protocol that allows the analyses of N-ras sequences has been developed. This reverse transcription-polymerase chain reaction (RT-PCR)/NIRCA protocol can allow the study of this proto-oncogene in every day clinical practice, rapidly facilitating the validation of the diagnostic and prognostic value of N-ras mutational analyses in patients with hematologic malignancies.

Activation of the TGF-beta/activin-Smad2 pathway during allergic airway inflammation

Changes in the levels of transforming growth factor (TGF)-beta cytokines or receptors observed during the progression of several inflammatory and fibrotic disorders have been used to implicate these cytokines in the pathophysiology of these diseases. Although correlative, these studies were inconclusive because they were unable to demonstrate actual continuous TGF-beta-mediated signaling in the involved tissues. We reasoned that the phosphorylation state and subcellular localization of Smad2, the intracellular effector of TGF-beta/activin-mediated signaling, could be used as a marker of active signaling mediated by these cytokines in situ. We therefore used an experimental model of ovalbumin-induced allergic airway inflammation and were able to demonstrate a dramatic increase in the numbers of bronchial epithelial, alveolar, and infiltrating inflammatory cells expressing nuclear phosphorylated Smad2 within the allergen-challenged lungs. This was accompanied by strong upregulation of the activin receptor ALK-4/ActR-IB and redistribution of the TGF-beta responsive ALK-5/TbetaR-I. Although levels of TGF-beta1, TGF-beta2, and TGF-beta3 messenger RNA (mRNA) were marginally altered, the level of activin mRNA was strongly upregulated during the inflammatory response. Our data illustrate the usefulness of antiphosphorylated Smad antibodies in demonstrating active TGF- beta/activin-mediated signaling in vivo and strongly suggest that activin/Smad-mediated signaling could be a critical contributor in the pathophysiology of allergic pulmonary diseases.

"Lymphoid" chemokine messenger RNA expression by epithelial cells in the chronic inflammatory lesion of the salivary glands of Sjögren's syndrome patients: possible participation in lymphoid structure formation

OBJECTIVE

Many studies have shown that the microanatomic organization of infiltrating leukocytes in the salivary gland lesions of patients with Sjögren's syndrome (SS) resembles the structure of lymphoid organs. A newly defined set of chemokines referred to as "lymphoid," which orchestrate leukocyte microenvironmental homing and contribute to the formation of lymphoid structures, provides directional clues. The aim of this study was to investigate the possible existence of "lymphoid" chemokines in the chronic inflammatory lesions of SS patients and thus validate their potential involvement in the disease process.

METHODS

Twelve patients with primary SS, 3 patients with secondary SS, 4 patients with other autoimmune disorders, and 4 control individuals were the subjects of this study. Reverse transcriptase-polymerase chain reaction analysis was performed in order to examine the messenger RNA (mRNA) expression of "lymphoid" chemokines. Furthermore, in situ hybridization studies revealed chemokine mRNA localization. Immunohistochemistry was also applied in order to identify the cell types that expressed the chemokine mRNA.

RESULTS

STCP-1/monocyte-derived chemokine and TARC mRNA were expressed in the majority of patients with primary and secondary SS, in 2 of 4 patients with other autoimmune disorders, and in 2 of 4 controls. BCA-1, ELC, and PARC mRNA were only detected in patients with primary and secondary SS. SLC mRNA was also detected in 1 non-SS patient. The main cellular sources of chemokine mRNA were ductal epithelial cells and infiltrating mononuclear leukocytes.

CONCLUSION

The expression pattern of "lymphoid" chemokine mRNA points further to the role of epithelial cells in the pathogenesis of SS and offers new insight into the potential mechanisms that could be involved in leukocyte attraction and in the in situ formation of secondary lymphoid tissue structures.

Amplification of IS6110 sequence for detection of Mycobacterium tuberculosis complex in HIV-negative patients with fever of unknown origin (FUO) and evidence of extrapulmonary disease

OBJECTIVES

Extrapulmonary tuberculosis (TB) constitutes the main cause of classic fever of unknown origin (FUO) in many populations. The aim of this study was to improve the diagnostic field of the disease using a nested polymerase chain reaction (PCR) assay, specific for the IS6110 insertion element of Mycobacterium tuberculosis complex, in order to achieve a more timely diagnosis and treatment.

SETTING

Twenty-four, HIV-negative classic FUO patients who were admitted to the Regional Hospital of Alexandroupolis between April 1997 and July 1999.

SUBJECTS AND DESIGN

The above patients were considered as putative extrapulmonary TB after 3 weeks of in-patient investigation and underwent exhaustive examination for diagnosis of the disease. For this purpose, specimens were obtained from peripheral blood and bone marrow from these patients, as well as from damaged tissues, and analysed by both PCR and conventional methods. Anti-tuberculous treatment was initiated in 16 out of 24 patients and the response to this regimen was considered as the final criterion for diagnosis of tuberculosis.

RESULTS

Extrapulmonary TB was established in 11 patients. The PCR-based methodology, when applied to samples derived from bone marrow aspirations and suspected damaged tissues, was able to diagnose 10 of them, whereas the conventional methods were able to detect only two.

CONCLUSIONS

Our results confirm the diagnostic value of molecular detection of M. tuberculosis in cases of FUO, thus supporting the application of PCR in tissue samples suspected of bacillus infection. Furthermore, our studies demonstrate that bone marrow aspiration specimens constitute an alternative, easy, safe and reliable source for such PCR analysis.

Reduced formation of phosphatidic acid upon B-cell receptor triggering of mouse B-lymphocytes lacking Bruton's tyrosine kinase

Btk deficient (BtkM) mouse B-lymphocytes do not proliferate when stimulated with anti-immunoglobulin (anti-Ig) antibodies. In order to characterize the molecular basis of this unresponsiveness we have compared early signal transduction pathways triggered by ligating the B cell antigen receptor (BCR) of purified resting B cells from normal C57BL/6 (wild-type) and BtkM mice on C57BL/6 background. BCR-induced signalling events that occur during the first few minutes of activation, such as bulk tyrosine phosphorylations, mitogen-activated protein kinase (MAPK) activation, PI3-kinase dependent PKB/Akt kinase phosphorylation/activation and PLCgamma2 tyrosine phosphorylation are comparable in wild type and BtkM B cells. However, the initial extracellular calcium influx is reduced and the BCR-induced accumulation of phosphatidic acid (PA) display a more transient profile in the BtkM cells. BCR ligation did not induce detectable phosphatidyl-choline PLD activity, suggesting that the reduced PA is owing to a reduction in the phospho-inositide hydrolysis. These findings further support the notion that the proliferative defect of Btk deficient mouse B cells in response to anti-immunoglobulin stimulation stems from a failure to sustain phospholipase-dependent signalling.

Regulation of germline promoters by the two human Ig heavy chain 3' alpha enhancers

The human IgH 3' enhancers, located downstream of each of the two Calpha genes, modulate germline (GL) transcription of the IgH genes by influencing the activity of promoter-enhancer complexes upstream of the switch and intervening (I) regions. The regulation of GL alpha1 and alpha2 promoters by different human 3' enhancer fragments was investigated in cell lines representing various developmental stages. Both alpha1HS1,2 and alpha2HS1,2 fragments show equally strong enhancer activity on the GL alpha1 and alpha2 promoters in both orientations when transiently transfected into a number of mature B cell line (DG75, CL-01, and HS Sultan). However, there is no activity in a human pre-B cell line (NALM-6) nor a human T cell line (Jurkat). HS3 shows no enhancer activity by itself in any of the cell lines, whereas a modest effect is noted using HS4 in the three mature B cell lines. However, the combination of the alpha2HS3-HS1,2-HS4 fragments, which together form a potential locus control region, displays a markedly stronger enhancer activity than the individual fragments with a differential effect on the alpha1 and alpha2 promoters as compared with the gamma3 promoter. Our results suggest that the human GL alpha promoter may be regulated by two independent pathways. One pathway is induced by TGF-beta1 which directs IgA isotype switch through activation of the GL alpha promoter and no TGF-beta1-responsive elements are present in the different 3' enhancer fragments. The other route is through the human 3' enhancer regions that cis-up-regulate the GL alpha promoter activity in mature B cells.

Smad and AML proteins synergistically confer transforming growth factor beta1 responsiveness to human germ-line IgA genes

Transcription of germ-line immunoglobulin heavy chain genes conditions them to participate in isotype switch recombination. Transforming growth factor-beta1 (TGF-beta1) stimulates promoter elements located upstream of the IgA1 and IgA2 switch regions, designated Ialpha1 and Ialpha2, and contributes to the development of IgA responses. We demonstrate that intracellular Smad proteins mediate activation of the Ialpha1 promoter by TGF-beta. TGF-beta type 1 receptor (ALK-5), activin type IB receptor (ALK-4), and the "orphan" ALK-7 trans-activate the Ialpha1 promoter, thus raising the possibility that other members of the TGF-beta superfamily can also modulate IgA synthesis. Smads physically interact with the AML family of transcription factors and cooperate with them to activate the Ialpha1 promoter. The Ialpha1 element provides a canapé of interspersed high and low affinity sites for Smad and AML factors, some of which are indispensable for TGF-beta responsiveness. While AML.Smad complexes are formed in the cytoplasm of DG75 and K562 cells constitutively, only after TGF-beta receptor activation, novel Smad3.Smad4.AML complexes are detected in nuclear extracts by EMSA with Ialpha1 promoter-derived probes. Considering the wide range of biological phenomena that AMLs and Smads regulate, the physical/functional interplay between them has implications that extend beyond the regulation of class switching to IgA.

X-chromosome inactivation and mutation pattern in the Bruton's tyrosine kinase gene in patients with X-linked agammaglobulinemia. Italian XLA Collaborative Group

BACKGROUND

The diagnosis of X-linked agammaglobulinemia (XLA) is not always clearcut. Not all XLA conform to the classic phenotype and less than 50% of affected boys have a family history of immunodeficiency. Mutations in the gene for Bruton's tyrosine kinase (BTK) are responsible for the majority of agammaglobulinemia cases. However, a certain proportion of patients may have mutations involving other genes, although they show with an XLA phenotype. We performed BTK gene mutation analysis in 37 males with presumed XLA and analyzed the pattern of X-chromosome inactivation (XCI) in 31 mothers to evaluate the relevance of these approaches to diagnosis and genetic counseling.

MATERIALS AND METHODS

Twenty affected males with a sporadic occurrence and 17 familial cases belonging to nine families were enrolled within the framework of the Italian Multicenter Clinical Study on XLA. We used non-isotopic RNase cleavage assay (NIRCA), followed by cDNA sequence determination to screen for BTK mutations and X-chromosome inactivation analysis for carrier detection.

RESULTS

Using the cDNA-based approach, the identification of BTK gene abnormalities confirmed the clinical diagnosis of XLA in 31 of 37 affected infants. Missense was the most frequent mutational event and the kinase domain was mostly involved. In addition, nine novel mutations were identified. In sporadic cases, BTK gene abnormalities were identified in 9 out of 10 patients whose mothers had a nonrandom pattern of XCI and in 5 out of 6 patients whose mother had a random pattern of XCI. With the exception of one family, all patients with a familial occurrence and born to mothers with a nonrandom pattern of XCI had mutations of the BTK gene.

CONCLUSIONS

Our findings indicate that in sporadic cases BTK gene sequencing is the only reliable tool for a definitive diagnosis of XLA and support XCI as the first diagnostic tool in the mothers of affected males in multiple generations. Furthermore, our molecular analysis confirms that 10-20% of BTK-unaltered patients have disorders caused by defects in other genes.

Identification of nine novel mutations in the Bruton's tyrosine kinase gene in X-linked agammaglobulinaemia patients

Mutations in the Bruton's tyrosine kinase (BTK ) gene are responsible for X-linked Agammaglobulinemia (XLA), an immunodeficiency caused by a block in B cell differentiation. Non Isotopic RNAse Cleavage Assay (NIRCA), followed by sequencing was used to screen for BTK mutations in 11 Italian XLA patients. Nine novel mutations were identified: 6 missense (Y39S, L512P, L512Q, R544G, S578Y, E589K), one non-sense (Q260X), one frameshift (1599-1602del GCGC) and one in-frame insertion (2037-2038insTTTTAG), that represents the first case of premature stop codon introduction in the BTK coding frame. These data support the high molecular heterogeneity of BTK gene in XLA disease and provide new insight to the diagnosis and to the role of BTK domain in XLA and in B cell signal transduction and development. Hum Mutat 15:117, 2000.

Three chemokines with potential functions in T lymphocyte-independent and -dependent B lymphocyte stimulation

Three clustered mouse chemokine genes, ABCD-1, -2 and -3, are all expressed highly in dendritic cells and, at various levels, in activated B cells. T cell-independently activated B cells express ABCD-1 and -2, but not -3. T cell-dependently activated B cells express all three. ABCD-1 attracts activated CD8+ cytotoxic T cells and CD4+ helper T cells of type 1 and 2. ABCD-2 preferentially attracts type 2 helper T cells, while ABCD-3 does not attract T cells at all. Both ABCD-1 and ABCD-2 bind to the same receptor (CCR4). In addition, ABCD-1 binds to a second, unknown, receptor on a separate T cell population. The three chemokines might guide T cell-independent as well as -dependent responses with two types of CD4+ T cells.

B cell development in the spleen takes place in discrete steps and is determined by the quality of B cell receptor-derived signals

Only mature B lymphocytes can enter the lymphoid follicles of spleen and lymph nodes and thus efficiently participate in the immune response. Mature, long-lived B lymphocytes derive from short-lived precursors generated in the bone marrow. We show that selection into the mature pool is an active process and takes place in the spleen. Two populations of splenic B cells were identified as precursors for mature B cells. Transitional B cells of type 1 (T1) are recent immigrants from the bone marrow. They develop into the transitional B cells of type 2 (T2), which are cycling and found exclusively in the primary follicles of the spleen. Mature B cells can be generated from T1 or T2 B cells. Mice with genetic deletions of elements participating in the B cell receptor signaling cascade display developmental arrest at the T1 or T2 stage. The analysis of these defects showed that the development of T2 and mature B cells from T1 precursors requires defined qualitative and quantitative signals derived from the B cell receptor and that the induction of longevity and maturation requires different signals.

Synergistic activation of the human Btk promoter by transcription factors Sp1/3 and PU.1

Analysis of the human Bruton's agammaglobulinemia tyrosine kinase (Btk) gene promoter revealed that 280 bp upstream of the transcriptional start site is sufficient for a cell restricted expression pattern. Here, the interplay of the transcription factors Sp1, Sp3, and PU.1 binding to this promoter area was analysed. All three proteins are able to independently activate the promoter in Drosophila Schneider (SL2) cells lacking endogenous Sp- or PU.1-like activities. Furthermore, PU.1 is able to act synergistically with Sp1 as well as Sp3 to transactivate the promoter. This transactivation is mediated through adjacent binding sites rather than through the more distant Sp binding site, suggesting a possible direct interaction between PU.1 and Sp1/3. Expression of Btk was found in ES cells and levels of expression were the same as in ES cells with a targeted deletion of the Sp1 gene, suggesting that Sp3 acts as a positive regulator of Btk in vivo, in the absence of Sp1.

Bruton's tyrosine-kinase-deficient murine B lymphocytes fail to enter S phase when stimulated with anti-immunoglobulin plus interleukin-4

One of the earliest recognized defects of B cells carrying the xid mutation in the gene encoding for Bruton's tyrosine kinase (Btk) was their inability to proliferate in response to anti-immunoglobulin plus interleukin (IL)-4 stimulation. Previous attempts to define the stage at which this proliferative block occurred using xid B cells provided dissimilar results. We decided to reinvestigate this question using B cells from C57BL/6-Btk-protein-deficient (BtkM) mice. Upon stimulation with anti-IgM and IL-4, BtkM cells increase in size and up-regulate early activation markers such as CD69 and B7-2, however, they do not progress into the cell cycle further than a very early G1 stage. They down-regulate the cyclin-dependent kinase (cdk) inhibitor p27 to some extent but fail to up-regulate the G1-phase cyclins D2 and E and the retinoblastoma protein (pRb) remains hypo-phosphorylated. While approximately 25% of the wild-type cells enter S phase after 36 h stimulation, only 1% of the BtkM cells do so. The proliferative responsiveness of the BtkM cells is restored when the phorbol ester phorbol 12,13-di-butyrate (PDBu) is added to the anti-IgM plus IL-4 cultures. Collectively, our data demonstrate that a dramatically reduced frequency of responsive cells underlies the low proliferation of anti-IgM plus IL-4-stimulated Btk-deficient B cells and point towards an early block in the G1 phase due to inadequate activation of a pathway that regulates PKC activation.

AML and Ets proteins regulate the I alpha1 germ-line promoter

The immunoglobulin heavy chain (IgH) class switch recombination of B lymphocytes preferentially targets unrearranged IgH genes that have already been rendered transcriptionally active. Transcription of the germ-line IgH genes is controlled by intervening (I) regions upstream of their switch regions. The I alpha1 promoter activates transcription of the human germ-line C alpha1 gene for IgA1 and mediates the transforming growth factor (TGF)-beta1 responsiveness of this locus. Here we show that the I alpha1 promoter contains several binding sites for the AML/PEBP2/CBF family of transcription factors and that AML and Ets proteins are major regulators of the basal and TGF-beta-inducible promoter activity. Our data constitute a starting point for studies to elucidate the molecular mechanism by which TGF-beta regulates IgA production.

Independent and opposing roles for Btk and lyn in B and myeloid signaling pathways

Transphosphorylation by Src family kinases is required for the activation of Bruton's tyrosine kinase (Btk). Differences in the phenotypes of Btk-/- and lyn-/- mice suggest that these kinases may also have independent or opposing functions. B cell development and function were examined in Btk-/-lyn-/- mice to better understand the functional interaction of Btk and Lyn in vivo. The antigen-independent phase of B lymphopoiesis was normal in Btk-/-lyn-/- mice. However, Btk-/-lyn-/- animals had a more severe immunodeficiency than Btk-/- mice. B cell numbers and response to T cell-dependent antigens were reduced. Btk and Lyn therefore play independent or partially redundant roles in the maintenance and function of peripheral B cells. Autoimmunity, hypersensitivity to B cell receptor (BCR) cross-linking, and splenomegaly caused by myeloerythroid hyperplasia were alleviated by Btk deficiency in lyn-/- mice. A transgene expressing Btk at approximately 25% of endogenous levels (Btklo) was crossed onto Btk-/- and Btk-/-lyn-/- backgrounds to demonstrate that Btk is limiting for BCR signaling in the presence but not in the absence of Lyn. These observations indicate that the net outcome of Lyn function in vivo is to inhibit Btk-dependent pathways in B and myeloid cells, and that Btklo mice are a useful sensitized system to identify regulatory components of Btk signaling pathways.

Absence of Bruton's tyrosine kinase (Btk) mutations in patients with acute myeloid leukaemia

Bruton's tyrosine kinase (Btk) is a non-receptor protein tyrosine kinase (PTK) that is expressed in all haemopoietic lineages except mature T cells and plasma cells. Despite the broad range of expression. mutations that inactivate this molecule affect primarily the development of the B-cell lineage. As a PTK, Btk could potentially be involved directly or indirectly in the processes that relate to the malignant transformation of all the cell lineages where this molecule is expressed. Previous studies have failed to demonstrate mutations in patients with B-cell origin acute lymphoblastic leukaemia (ALL). We have utilized a recently developed method that enables the rapid and convenient detection of mutations at the cDNA level, namely, the non-isotopic RNase cleavage assay (NIRCA) to analyse Btk sequences from 27 patients with different types of acute myeloid leukaemia (AML). The only alteration that we observed was a polymorphism at position 2031. This polymorphism has already been seen in previous studies. Furthermore, using the same methodology, we identified the Btk mutations in six XLA (X-linked agammaglobulinaemia) patients. Our results, although they do not exclude the involvement of Btk mutations in the development or progression of some type of AML, nevertheless suggest that such mutations do not constitute a major co-factor in the development of myeloid malignancies.

Activated murine B lymphocytes and dendritic cells produce a novel CC chemokine which acts selectively on activated T cells

Genes were isolated using the suppression subtractive hybridization method by stimulation of pro/pre B cells with anti-CD40 and interleukin (IL)-4 to mature S mu-Sepsilon-switched cells. One of the strongly upregulated genes encodes a novel murine CC chemokine we have named ABCD-1. The ABCD-1 gene has three exons separated by 1. 2- and 2.7-kb introns. It gives rise to a 2.2-kb transcript containing an open reading frame of 276 nucleotides. Two polyadenylation sites are used, giving rise to cDNAs with either 1550 or 1850 bp of 3' untranslated regions. The open reading frame encodes a 24 amino acid-long leader peptide and a 68 amino acid-long mature protein with a predicted molecular mass of 7.8 kD. ABCD-1 mRNA is found in highest quantities in activated splenic B lymphocytes and dendritic cells. Little chemokine mRNA is present in lung, in unstimulated splenic cells, in thymocytes, and in lymph node cells. No ABCD-1 mRNA is detected in bone marrow, liver, kidney, or brain, in peritoneal exudate cells as well as in the majority of all unstimulated B lineage cells tested. It is also undetectable in Concanavalin A-activated/IL-2-restimulated splenic T cells, and in bone marrow-derived IL-2-induced natural killer cells and IL-3-activated macrophages. Recombinant ABCD-1 revealed a concentration-dependent and specific migration of activated splenic T lymphoblasts in chemotaxis assays. FACS(R) analyses of migrated cells showed no preferential difference in migration of CD4(+) versus CD8(+) T cell blasts. Murine as well as human T cells responded to ABCD-1. Freshly isolated cells from bone marrow, thymus, spleen, and lymph node, IL-2-activated NK cells, and LPS-stimulated splenic cells, all did not show any chemotactic response. Thus, ABCD-1 is the first chemokine produced in large amounts by activated B cells and acting selectively on activated T lymphocytes. Therefore, ABCD-1 is expected to play an important role in the collaboration of dendritic cells and B lymphocytes with T cells in immune responses.

Btk dosage determines sensitivity to B cell antigen receptor cross-linking

Mutations in Btk result in the B cell immunodeficiencies X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (xid) in mice. Btk is a critical component of signaling pathways regulating B cell development and function. We used a genetic approach to determine whether Btk is also limiting for these processes. One allele of a murine Btk transgene expressed a dosage of Btk (25% of endogenous levels in splenic B cells) sufficient to restore normal numbers of phenotypically mature conventional B cells in xid mice. 2,4,6-trinitrophenyl-Ficoll response, anti-IgM-induced proliferation, B1 cell development, and serum IgM and IgG3 levels remained significantly impaired in these animals. B cells from Btk -/- transgenic mice also responded poorly to anti-IgM, indicating that the xid mutation does not create a dominant negative form of Btk. Response to 2,4,6-trinitrophenyl-Ficoll and B cell receptor cross-linking were increased 3- to 4-fold in xid mice homozygous for the transgene. These results demonstrate that Btk is a limiting component of B cell antigen receptor signaling pathways and suggest that B cell development and response to antigen may require different levels of Btk activity.

Structural analysis of human gamma 3 intervening regions and switch regions: implication for the low frequency of switching in IgG3-deficient patients

High and low serum concentrations of IgG3 are associated with the human G3m(b) and G3m(g) allotypes, respectively. In the present study, we analyzed the structure of the S gamma 3 and I gamma 3, the switch frequency, switch breakpoints and the levels and initiation sites of I gamma 3 transcripts both in normal blood donors expressing (b) or (g) allotypes as well as IgG3-deficient (D) patients. A low switch frequency to gamma 3 was found in the (g) allotype IgG3D patients which may be caused in part by the allotype-associated mutations in the S gamma 3 region and in part by additional individual mutations observed in the A (SNAP) and B (SNIP/ NF-kappa B) sites in the S gamma 3 repeat region. A higher I gamma 3 germ-line (GL) transcriptional rate was seen in cells from the IgG3D patient, suggesting that low levels of GL I gamma 3 transcripts are not a major contributing factor to the defect. However, individual mutations in the I gamma 3 region and differential splicing of GL I gamma 3 transcripts were found which may affect the switching process.

Development of CLL in individuals with mild lymphocytosis, without bone marrow infiltration, but with evidence of a monoclonally expanded population in peripheral blood

Mild lymphocytosis (< 10 x 10(9)/L) is a common finding in routine blood tests. When it persists, it raises the question of whether this disorder is an early manifestation of chronic lymphocytic leukemia (CLL). If it is accompanied by bone marrow infiltration, it can be safely considered as a sign of CLL. The aim of this study was to analyze retrospectively the usefulness of immunophenotyping and immunogenotyping for early detection of lymphocyte clonality in ambiguous cases of lymphocytosis without bone marrow infiltration. Twenty-six healthy individuals, 47 to 77 years old, with an absolute lymphocyte count (ALC) at the "onset" of the disorder between 4 x 10(9)/L and 9 x 10(9)/L, without marrow infiltration, were studied and followed for a period of 31 to 51 months. CD19, CD20, CD5, CD2, CD4, CD8 surface markers and amplification of the Ig heavy chain CDR-3 locus were used for immunophenotypic and genotypic analysis, respectively. Our studies indicate that immunophenotyping alone is sufficient and superior to CDR-3 locus amplification for the early detection of lymphocyte clonality in peripheral blood. Furthermore, the high frequency of CLL development in individuals with established monoclonality strongly suggests that patients with mild borderline lymphocytosis, even without bone marrow infiltration, have to be followed for progression to CLL and its possible complications.

Impaired B cell maturation in mice lacking Bruton's tyrosine kinase (Btk) and CD40

Mutations in Bruton's tyrosine kinase (Btk) gene, in mice, result in reduced numbers and responses of peripheral B cells. Surface Ig-mediated signaling is defective in Btk mutant B cells as they do not proliferate upon slg cross-linking and lack thymus-independent (TI) type II responses. Signals through sIg and CD40 play a critical role in B cell maturation. To investigate the consequences of the lack of both Btk and CD40 on B cell development and function, mice were generated that were homozygous for targeted mutations in the Btk and the CD40 genes (BtkMCD40M). The CD40 mutation (CD40M) had a synergistic effect on the BtkM defects. In BtkMCD40M mice the number of B cells was reduced 3- to 4-fold compared to BtkM mice and mature B cells (IgMlow/IgDhigh) were virtually absent; serum levels of all Ig isotypes were diminished; and antibody responses to TI-I TI-II and thymus-dependent antigens were impaired. Furthermore, although wild-type BtkM and CD40M mice produced germinal centers in response to TI-I antigen, the BtkMCD40M mice did not. Maturational and functional B cell defects in BtkMCD40M mice may result from a combination of intrinsic B cell defects, lack of CD40L-dependent T cell help and microenvironmental defects. These data suggest that signals through Btk and CD40 are necessary for the production and maintenance of the mature B cell.

Cell specific expression of human Bruton's agammaglobulinemia tyrosine kinase gene (Btk) is regulated by Sp1- and Spi-1/PU.1-family members

Bruton's agammaglobulinemia tyrosine kinase (Btk) is a cytoplasmic tyrosine kinase involved in the human disease X-linked agammaglobulinemia (XLA). The gene is expressed in all hematopoietic cells with the exception of T-cells and plasma cells. For this expression pattern the first 280 bp upstream of the major transcriptional start site seems to be sufficient. In vitro footprinting analysis within this part of the promoter revealed two Sp1 binding sites as well as a PU-box. The transcription factor Spi-1/PU.1 as well as the closely related factor Spi-B bound to the PU-box in B-cells. In the erythroleukemia cell line K562, due to the absence of Spi-B, only PU.1 bound to the Btk promoter. Mutation of either site reduced the expression in transient transfection experiments. However, mutation of the PU box had no effect in the T-cell line Jurkat, where none of the Spi-1 family members is expressed. In addition Spi-B as well as PU.1 were able to transactivate Btk expression. In fetal liver of PU.1-/- mice, which lack lymphoid and myeloid cells, expression of Btk was reduced two- to threefold but not abolished. Collectively this study shows that expression of the Btk gene is regulated by the combined action of Sp1- and PU.1-family members.

A Drosophila hsp70 gene contains long, antiparallel, coupled open reading frames (LAC ORFs) conserved in homologous loci

A clone isolated from a Drosophila auraria heat-shock cDNA library presents two long, antiparallel, coupled (LAC) open reading frames (ORFs). One strand ORF is 1,929 nucleotides long and exhibits great identity (87.5% at the nucleotide level and 94% at the amino acid level) with the hsp70 gene copies of D. melanogaster, while the second strand ORF, in antiparallel in-frame register arrangement, is 1,839 nucleotides long and exhibits 32% identity with a putative, recently identified, NAD(+)-dependent glutamate dehydrogenase (NAD(+)-GDH). The overlap of the two ORFs is 1,824 nucleotides long. Computational analysis shows that this LAC ORF arrangement is conserved in other hsp70 loci in a wide range of organisms, raising questions about possible evolutionary benefits of such a peculiar genomic organization.

The human I alpha 1 region contains a TGF-beta 1 responsive enhancer and a putative recombination hotspot

It appears that the switch recombination machinery of a B lymphocyte targets preferentially unrearranged heavy chain genes that have been rendered transcriptionally active. Transcriptional activation of the 'germline' human C alpha 1 and C alpha 2 genes is triggered by TGF-beta 1 and is controlled by proximal positive and distal negative regulatory elements residing upstream of the alpha 1 and alpha 2 switch regions respectively. In this report we characterize the positive proximal regulatory elements and analyse their interaction with DNA binding proteins. Our data demonstrate that a 100 bp fragment that contains a cAMP responsive element (CRE)/activating transcription factor (ATF) motif, a putative Ets binding site and an element that is created by two previously described neighbouring direct repeats (DRE), can increase the basal level of transcription and confer TGF-beta 1 inducibility to a heterologous promoter in an orientation- and position-independent manner. Ubiquitously expressed DNA binding proteins interact specifically with the CRE/ATF, the Ets site and the DRE element. Additionally, nuclear proteins interact with sequences which are located downstream of this enhancer are not essential for transcription in the transient expression assays utilized; however, they contain motifs that have been previously implicated in regulating DNA recombination events. These motifs include a Chi motif and a Chi-like element previously found in the recombination hotspot region of the Bcl-2 proto-oncogene and close to chromosomal breakpoints in T-ALL lines. Our findings raise the possibility that the intervening region associated regulatory elements in addition to regulating the transcriptional activation of the Ig heavy chain genes could also facilitate the physical interaction of transcription and recombination controlling molecular mechanisms.

Identification of Btk mutations in 20 unrelated patients with X-linked agammaglobulinaemia (XLA)

X-linked agammaglobulinaemia (XLA) is an inherited immunodeficiency resulting from mutations in the gene for a cytoplasmic protein tyrosine kinase (Btk). We have utilised reverse-transcription-based PCR in combination with the chemical cleavage and mismatch technique (CCM) to screen for Btk mutations in 42 unrelated patients having classical XLA or 'leaky' XLA-like phenotypes. A variety of mutations, including point mutations, large deletions and splicing defects were detected using this strategy. In total, 20 mutations were found in these patients. All the mutations were different with the exception of three unrelated patients who all showed the same Arg-->His amino acid substitution (R641H) at a highly-conserved residue in the kinase domain. We have also used structural modelling of the Btk kinase domain to predict how two different amino acid substitution mutations at highly-conserved residues are likely to affect the Btk kinase activity.

Genomic organization of mouse and human Bruton's agammaglobulinemia tyrosine kinase (Btk) loci

Btk is a cytoplasmic protein tyrosine kinase (PTK) that has been directly implicated in the pathogenesis of X-linked agammaglobulinaemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. We have isolated phage and cosmid clones that allowed us to deduce the genomic structure of mouse and human Btk loci. The mouse and human genes are contained within genomic regions that span approximately 43.5 kb and 37.5 kb, respectively. Both loci contain 18 coding exons ranging between 55 and 560 bp in size with introns ranging in size from 164 bp to approximately 9 kb. The 5'-untranslated regions are encoded by single exons located approximately 9 kb upstream of the first coding exon. Exon 18 encodes for the last 23 carboxyl-terminal amino acids and the entire 3'-untranslated region. The location of intron/exon boundaries in the catalytic domains of the mouse and human Btk loci differs from that found in other described sub-families of intracellular PTKs, namely that of Src, Fes/Fer, Csk, and Abl/Arg. This observation is consistent with the classification of Btk together with the recently characterized kinases, Tec and Itk, into a separate sub-family of cytoplasmic PTKs. Putative transcription initiation sites in the mouse and human Btk loci have been determined by using the rapid amplification of cDNA ends assay. Similar to many other PTK specific genes, the putative Btk promoters lack obvious TATAA and CAAAT motifs. Putative initiator elements and potential binding sites for Ets (PEA-3), zeste, and PuF transcription factors are located within the 300 bp which are located upstream of the major transcription start site in both species. These sequences can mediate promoter activity when placed upstream of a promotorless chloramphenicol acetyl transferase reporter gene in an orientation-dependent manner. The present analysis will significantly facilitate the mutational analyses of patients with XLA and the further characterization of the function and regulation of the Btk molecule.

Genomic organization of mouse and human Bruton's agammaglobulinemia tyrosine kinase (Btk) loci

Btk is a cytoplasmic protein tyrosine kinase (PTK) that has been directly implicated in the pathogenesis of X-linked agammaglobulinaemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. We have isolated phage and cosmid clones that allowed us to deduce the genomic structure of mouse and human Btk loci. The mouse and human genes are contained within genomic regions that span approximately 43.5 kb and 37.5 kb, respectively. Both loci contain 18 coding exons ranging between 55 and 560 bp in size with introns ranging in size from 164 bp to approximately 9 kb. The 5'-untranslated regions are encoded by single exons located approximately 9 kb upstream of the first coding exon. Exon 18 encodes for the last 23 carboxyl-terminal amino acids and the entire 3'-untranslated region. The location of intron/exon boundaries in the catalytic domains of the mouse and human Btk loci differs from that found in other described sub-families of intracellular PTKs, namely that of Src, Fes/Fer, Csk, and Abl/Arg. This observation is consistent with the classification of Btk together with the recently characterized kinases, Tec and Itk, into a separate sub-family of cytoplasmic PTKs. Putative transcription initiation sites in the mouse and human Btk loci have been determined by using the rapid amplification of cDNA ends assay. Similar to many other PTK specific genes, the putative Btk promoters lack obvious TATAA and CAAAT motifs. Putative initiator elements and potential binding sites for Ets (PEA-3), zeste, and PuF transcription factors are located within the 300 bp which are located upstream of the major transcription start site in both species. These sequences can mediate promoter activity when placed upstream of a promotorless chloramphenicol acetyl transferase reporter gene in an orientation-dependent manner. The present analysis will significantly facilitate the mutational analyses of patients with XLA and the further characterization of the function and regulation of the Btk molecule.

Molecular analysis of IgA deficiency. Evidence for impaired switching to IgA

The most common form of primary immunodeficiency is IgA deficiency (IgAD). However, the molecular basis of this disease remains elusive. Therefore, to address this issue we made a systematic analysis of the molecular events leading to IgA production. B lymphocytes that produce IgA have undergone somatic rearrangement that joins the switch (S) mu to S alpha region with deletion of the intervening sequences. Examination of the resulting S mu/S alpha junctions in unstimulated PBMC from IgAD patients by nested primer PCR revealed a significant decrease in the number of the S mu/S alpha fragments. To obtain the antisense primers to generate the S mu/S alpha fragments, we sequenced the human S alpha 1 and the downstream region extending to the C alpha 1 locus. Similar to previously reported switch sequences, we also found the S alpha 1 to be predominantly composed of pentameric repeats GAGCT and GGGCT. The decrease in the number of S mu/S alpha fragments is consistent with a profound decrease in the C alpha membrane mRNA expression in unstimulated PBMC, as well as in the C alpha mRNA levels and IgA production in PWM-stimulated PBMC. Sequence analysis of the switch junctions from IgA-producing cell lines, control donors, and an IgAD patient showed direct joining in 8 of 9 cases examined. TGF-beta 1, previously shown to be the switch factor for human and mouse IgA, was also examined. No difference in the TGF-beta 1 mRNA levels in unstimulated PBMC between the control subjects and the IgAD patients were detected. Our findings indicate that the failure to switch to IgA-producing B lymphocytes, or an impaired survival of such cells, may be an important molecular mechanism in IgAD.

Molecular analysis of IgA deficiency. Evidence for impaired switching to IgA

The most common form of primary immunodeficiency is IgA deficiency (IgAD). However, the molecular basis of this disease remains elusive. Therefore, to address this issue we made a systematic analysis of the molecular events leading to IgA production. B lymphocytes that produce IgA have undergone somatic rearrangement that joins the switch (S) mu to S alpha region with deletion of the intervening sequences. Examination of the resulting S mu/S alpha junctions in unstimulated PBMC from IgAD patients by nested primer PCR revealed a significant decrease in the number of the S mu/S alpha fragments. To obtain the antisense primers to generate the S mu/S alpha fragments, we sequenced the human S alpha 1 and the downstream region extending to the C alpha 1 locus. Similar to previously reported switch sequences, we also found the S alpha 1 to be predominantly composed of pentameric repeats GAGCT and GGGCT. The decrease in the number of S mu/S alpha fragments is consistent with a profound decrease in the C alpha membrane mRNA expression in unstimulated PBMC, as well as in the C alpha mRNA levels and IgA production in PWM-stimulated PBMC. Sequence analysis of the switch junctions from IgA-producing cell lines, control donors, and an IgAD patient showed direct joining in 8 of 9 cases examined. TGF-beta 1, previously shown to be the switch factor for human and mouse IgA, was also examined. No difference in the TGF-beta 1 mRNA levels in unstimulated PBMC between the control subjects and the IgAD patients were detected. Our findings indicate that the failure to switch to IgA-producing B lymphocytes, or an impaired survival of such cells, may be an important molecular mechanism in IgAD.

Colocalization of X-linked agammaglobulinemia and X-linked immunodeficiency genes

Mice that bear the X-linked immunodeficiency (xid) mutation have a B lymphocyte-specific defect resulting in an inability to make antibody responses to polysaccharide antigens. A backcross of 1114 progeny revealed the colocalization of xid with Bruton's agammaglobulinemia tyrosine kinase (btk) gene, which is implicated in the human immune deficiency, X-linked agammaglobulinemia. Mice that carry xid have a missense mutation that alters a highly conserved arginine near the amino-terminus of the btk protein, Btk. Because this region of Btk lies outside any obvious kinase domain, the xid mutation may define another aspect of tyrosine kinase function.

Quantitative analysis of the expression and regulation of an activation-regulated phosphoprotein (oncoprotein 18) in normal and neoplastic cells

Activation of protein kinase C results in phosphorylation of a 19-kDa protein termed 19K. Isolation and sequence analysis of a cDNA encoding the 19K protein revealed that this protein has been studied in other systems under different names. The name oncoprotein 18 (Op18) has been proposed on the basis of a postulated up-regulation in neoplastic cells. In the present report we adopt the designation Op18 for the 19K protein, and quantify this phosphoprotein in a series of leukemia/lymphoma cell lines, a panel of non-transformed cells and some terminally differentiated cell types. For this purpose we have developed reagents allowing quantitative Western-blot analysis, and quantification of Op18 on the single cell level by flow cytometric analysis. The data demonstrates a pronounced up-regulation of the Op18 protein in most leukemia/lymphoma cell lines. The HPB-ALL cell line provided the most extreme case and expressed 7 x 10(6) Op18 molecules/cell, which compares with 0.65 x 10(6) Op18 molecules/cell in non-transformed lymphoblastoid cells. The expression of Op18 appears to be restricted to cell types with proliferative potential, but it is clear from our results that up-regulation of Op18 is uncoupled from cellular proliferation. Moreover, by employing an Epstein-Barr virus based shuttle vector, we expressed Op18 cDNA in lymphoblastoid cells. This resulted in a three to fourfold up-regulation of Op18 that did not have any detectable consequences for cell-surface phenotype or cell size. However, increased expression of Op18 resulted in a partial inhibition of cell proliferation. Taken altogether, the results suggest that up-regulation Op18 levels in leukemia/lymphoma cells are strongly associated with, but not a direct cause of tumour progression.

The gene involved in X-linked agammaglobulinaemia is a member of the src family of protein-tyrosine kinases

X-linked agammaglobulinaemia (XLA) is a human immunodeficiency caused by failure of pre-B cells in the bone marrow to develop into circulating mature B cells. A novel gene has been isolated which maps to the XLA locus, is expressed in B cells, and shows mutations in families with the disorder. The gene is a member of the src family of proto-oncogenes which encode protein-tyrosine kinases. This is, to our knowledge, the first evidence that mutations in a src-related gene are involved in human genetic disease.

Transcription of unrearranged Ig H chain genes in human B cell malignancies. Biased expression of genes encoded within the first duplication unit of the Ig H chain locus

Analysis of the H chain class switch recombination events on the productive and nonproductive alleles of several human B cell lines has demonstrated that, in the majority of cases, the two loci had rearranged different CH genes. The absence of a strict correlation between the two rearrangement events has been interpreted in favor of a stochastic switching mechanism in human B cells. Based on the accessibility model for the H chain class switch, we have considered an alternative explanation, namely, that transcriptional activation of more than one CH gene could render more than one isotype accessible for recombination. In order to test this possibility, we have stimulated a number of IgM-bearing B cell tumors and analyzed the transcriptional response of their unrearranged C gamma and C alpha H chain genes at the Ig class level by Northern hybridization and at the subclass level by RNA-RNA solution hybridization. Our data show that human clonal B cell populations can simultaneously express germ-line transcripts of both gamma and alpha genes. Our data also demonstrate a bias in the expression of the different isotypes in the B cell chronic lymphocytic leukemias analyzed, with the genes present with the first duplication unit of the H chain locus (gamma 3, gamma 1, and alpha 1) being expressed almost exclusively. These findings indicate that transcriptional activation of large chromosomal regions containing more than one CH gene could render all the genes available for recombination and, therefore, provide an explanation for the asymmetry in the rearrangement events that have previously been described in human B cell tumors. The possible relevance of our findings to the molecular mechanism of the H chain class switch is discussed.

Transcription of unrearranged Ig H chain genes in human B cell malignancies. Biased expression of genes encoded within the first duplication unit of the Ig H chain locus

Analysis of the H chain class switch recombination events on the productive and nonproductive alleles of several human B cell lines has demonstrated that, in the majority of cases, the two loci had rearranged different CH genes. The absence of a strict correlation between the two rearrangement events has been interpreted in favor of a stochastic switching mechanism in human B cells. Based on the accessibility model for the H chain class switch, we have considered an alternative explanation, namely, that transcriptional activation of more than one CH gene could render more than one isotype accessible for recombination. In order to test this possibility, we have stimulated a number of IgM-bearing B cell tumors and analyzed the transcriptional response of their unrearranged C gamma and C alpha H chain genes at the Ig class level by Northern hybridization and at the subclass level by RNA-RNA solution hybridization. Our data show that human clonal B cell populations can simultaneously express germ-line transcripts of both gamma and alpha genes. Our data also demonstrate a bias in the expression of the different isotypes in the B cell chronic lymphocytic leukemias analyzed, with the genes present with the first duplication unit of the H chain locus (gamma 3, gamma 1, and alpha 1) being expressed almost exclusively. These findings indicate that transcriptional activation of large chromosomal regions containing more than one CH gene could render all the genes available for recombination and, therefore, provide an explanation for the asymmetry in the rearrangement events that have previously been described in human B cell tumors. The possible relevance of our findings to the molecular mechanism of the H chain class switch is discussed.

Quantitative and qualitative analysis of human IgG subclass specific mRNA using solution hybridization

Four IgG subclasses have been identified in the human system. Despite the fact that they exhibit differences in their functional properties, antigenic properties and chemical composition and demonstrate age-related shifts in their expression, the genes coding for their constant regions show extensive homology at the nucleotide level (greater than 95%). The only parts of the C gamma genes that show significant variation among the different IgG subclasses are the exons coding for their hinge regions (less than 60%). Taking advantage of such sequence variation, we have developed specific RNA probes which allowed us to analyse the expression of the C gamma 1, C gamma 2, C gamma 3 and C gamma 4 genes at the mRNA level using solution hybridization. We have defined optimal conditions that allow the detection of picogram levels of IgG subclass specific mRNA, while keeping the cross-reactivity between the different probes below 2%. This approach will significantly facilitate studies aiming at characterizing the molecular mechanisms regulating the expression of the four human IgG heavy chain constant region genes.

Structure of TGF-beta 1-induced human immunoglobulin C alpha 1 and C alpha 2 germ-line transcripts

We have characterized the structure of the human immunoglobulin C alpha 1 and C alpha 2 germ-line transcripts that are synthesized upon treatment of human B lymphocytes with Branhamella catarrhalis (a B cell mitogen) and transforming growth factor beta 1 (TGF-beta 1). These transcripts initiate upstream of the switch alpha 1 and switch alpha 2 regions and contain, together with the C alpha 1 and C alpha 2 sequences, additional exons designated according to the generally accepted nomenclature I alpha 1 and I alpha 2 respectively. The I alpha exons are spliced directly onto the acceptor splice site of the CH1 domains of the C alpha 1 and C alpha 2 genes. As in other previously characterized germ-line transcripts, stop codons present in all three reading frames prevent translation of the C alpha 1 and C alpha 2 heavy-chain coding sequences. The longest open reading frame (ORF) present in the I exons can code for a polypeptide of only 26 amino acids. The human I alpha exons do not show any significant sequence homology with the corresponding mouse I alpha exon. However, comparison of nucleotide sequences of the genomic mouse and human I alpha regions demonstrated the presence of an approximately 300 bp highly conserved element located immediately upstream of the transcription initiation sites of the human and mouse C alpha germ-line transcripts. The isolation of the C alpha 1 and C alpha 2 germ-line transcripts will further facilitate the characterization of the molecular events responsible for the regulation of the human C alpha heavy chain loci.

TGF-beta 1 induces germ-line transcripts of both IgA subclasses in human B lymphocytes

Immunoglobulin (Ig) class switching appears to be preceded by induction of germ-line transcripts. In this report, we demonstrate that transforming growth factor beta (TGF-beta) induces germ-line transcripts of both the IgA subclasses (IgA1 and IgA2) in Branhamella catarrhalis (BC)-activated human spleen B cells. Two germ-line bands, one of approximately 1.85 kb and the other of approximately 1.6 kb, could be seen in cultures treated with TGF-beta. The approximately 1.85 kb band contains mRNA for a germ-line transcript of the membrane form. This band co-migrates with the productive secreted form of alpha mRNA. The other, shorter form of approximately 1.6 kb did not correlate in size with any known form of productive alpha mRNA and contained the secreted form of germ-line alpha mRNA. The induction of alpha germ-line transcripts was accompanied by a concomitant suppression of mu and gamma mRNA. We have also identified the location of a putative I alpha sequence (designated according to the generally accepted nomenclature) within approximately 0.5 kb upstream to the switch alpha (S alpha) region. The relative proportions of IgA-subclass-specific mRNA in TGF-beta-stimulated spleen B cells are concordant with the distribution pattern seen in pokeweed mitogen (PWM)-stimulated spleen mononuclear cells (MNC), which was 89 and 11% for the IgA1 and the IgA2 mRNA respectively. These results suggest a role of TGF-beta in regulating IgA class switching in human B lymphocytes.

Genomic organization of IgH gene compared with the expression of Bcl-2 gene in t(14;18)-positive lymphoma

In three lymphoma cell lines carrying t(14;18), named FL-18, FL-218, and FL-318, the genomic organization of IgH gene was compared with the expression of bcl-2 gene; the t(14;18) of the FL-18 cells occurred downstream from the major breakpoint cluster region (mbr) of a bcl-2 gene, and that of the FL-218 and FL-318 cells within the mbr. The FL-318 expressed the normal-sized bcl-2 transcript of 8.5-kb mRNA having the noncoding region 3 to the mbr, which was found in the FL-18, and the FL-218 lacking the intact bcl-2 gene did not. This finding suggests that in t(14;18)-positive lymphoma having the breakpoint within the mbr, transcription of the nontranslocated bcl-2 allele is not necessarily silent. In addition, the FL-218 and FL-318 expressed aberrant bcl-2 transcripts and heterogenous IgH transcripts lacking the VH region, and the bcl-2 transcripts each comigrated with parts of the sterile IgH mRNAs. The FL-318, which did not exhibit switch recombination on either IgH allele, contained abundant amounts of l gamma mRNAs, a prerequisite for the recombination into the C gamma locus. One of the I-mRNA species comigrated with the aberrant bcl-2 transcript. The FL-18 and FL-218 lacking the I gamma mRNAs had completed switch recombination of both IgH alleles. This result raises a possibility that deregulated bcl-2 transcription caused by t(14;18) is capable of playing a role in class switch recombination of IgH gene.

Production of sterile transcripts of C gamma genes in an IgM-producing human neoplastic B cell line that switches to IgG-producing cells

A human neoplastic B cell line SSK41 that expresses IgM on its surface switches spontaneously to IgG-producing cells. The SSK41 line contains a single immunoglobulin heavy-chain locus, the constant region (C) genes of which retain the germline configuration. The IgG-producing SSK41 line was purified by sorting, and shown to have undergone S-S recombination with deletion of the C mu gene. This line produced secretory and membrane-bound forms of gamma-chain mRNA. From cDNA libraries of a mixed population of IgM+/IgG+ SSK41 cells, we have isolated cDNA clones encoding the mature membrane-bound and secretory forms of the mu and gamma 1 heavy chains, all of which share the same variable region sequence. cDNA clones containing the mature gamma 3 chain were identified as well. We also isolated cDNA clones containing C gamma 1 and C gamma 3 sterile transcripts from the SSK41 line. These sterile transcripts contained additional exon sequences designated 'I' which were localized upstream of the C gamma 1 and C gamma 3 switch regions and homologous to murine counterparts. The I sequences were precisely spliced to the 5' ends of the corresponding C gamma exon sequences. These features of germline CH transcripts, i.e. the isotype specificity to class switching, location of exons, and sequences per se, are highly conserved between man and mouse.

Expression of B220 antigen on an interleukin 4- and interleukin 5-producing T-cell line

The murine T-cell line 2.19, originally used for cloning of interleukin 4 (IL-4) and IL-5, was analysed for surface marker characteristics using monoclonal antibodies and a FACS-4 analyser and found to be positive for the B220 antigen. Thus, this lymphokine-producing cell with characteristic T-cell markers expresses an antigen earlier thought to be specific for B cells. With two-colour fluorescence it was found that a small fraction (2-4%) of Thy 1+ spleen cells from normal CBA mice were also positive for B220.

Analysis by in situ hybridization of cells expressing mRNA for interleukin 4 in the developing thymus and in peripheral lymphocytes from mice

We have made use of RNA.RNA in situ hybridization to study the presence of cells producing mRNA for interleukin 4 (IL-4) in the developing thymus, spleen, and T-cell line 2.19. Approximately 1 of 300-400 spleen cells expressed detectable IL-4 mRNA 24 hr after their stimulation by the lectin concanavalin A. Spleen cells were also induced to express mRNA for IL-4 by stimulation with alloantigens. Splenocytes producing mRNA for IL-4 were detected 4 hr after stimulation by concanavalin A; the response peaked at approximately equal to 24 hr and was undetectable by 72 hr. Cyclosporin A inhibited the synthesis of IL-4 mRNA in the T-cell line 2.19, which had been induced by concanavalin A. Approximately 1 of 10 fetal thymocytes at day 14 of gestation expressed mRNA for IL-4 after their stimulation by phorbol 12-myristate 13-acetate and ionomycin. Both the frequency of fetal thymocytes expressing IL-4 mRNA and the amount of mRNA for IL-4 synthesized per cell sharply decreased at day 16 of gestation, and less than 1 of 1800 fetal thymocytes at day 18 of gestation expressed detectable IL-4 mRNA. Our results define the relative frequency of cells capable of expressing IL-4 mRNA after stimulation in vitro in the spleen and in the developing thymus. The data strongly argue for an important role of IL-4 in growth and differentiation of lymphoid cells, notably during T-cell development within the thymus.

Thymocyte clones from 14-day mouse embryos. I. State of T cell receptor genes, surface markers, and growth requirements

We have established in culture 13 clones from the thymus of a 14-d B10.BR mouse embryo and characterized 8 of them. All eight FT clones have the TCR-gamma and -beta genes in germline configuration. They express mRNA for the gamma, but not for the beta nor the alpha genes. All eight FT clones are Thy-1+, Ly-1+, LFA-1+, Pgp-1+, H-2K+, and T3-. Three phenotypes could be distinguished on the basis of Lyt-2, L3T4, and IL-2-R expression: Lyt-2+, L3T4-, IL-2-R+ (I); Lyt-2+, L3T4-, IL-2-R- (II); and Lyt-2+, L3T4+, IL-2-R+ (III) cells. All eight clones grow in rIL-4 and six clones also proliferate in rIL-2. Antibodies specific for IL-2-R inhibit their response to rIL-2 but not to rIL-4. The eight FT clones synthesize mRNA for IL-4 after stimulation in vitro and none of them exhibit cytolytic activity or helper function for B lymphocytes. We conclude that the FT clones are at a very early stage of T cell development, that the expression of Lyt-2 and L3T4 surface molecules can precede that of the antigen receptor, and that the same fetal thymocyte can use both IL-4 and IL-2 as growth factor.