Polarity of T cell shape, motility, and sensitivity to antigen

T cell activation requires contact with APCs. We used optical techniques to demonstrate T cell polarity on the basis of shape, motility, and localized sensitivity to antigen. An intracellular Ca2+ clamp showed that T cell shape and motility are extremely sensitive to changes in [Ca2+]i (Kd = 200 nM), with immobilization and rounding occurring via a calcineurin-independent pathway. Ca2+ dependent immobilization prolonged T cell contact with the antigen-presenting B cell; buffering the [Ca2+]i signal prevented the formation of stable cell pairs. Optical tweezers revealed spatial T cell sensitivity to antigen by controlling placement on the T cell surface of either B cells or alpha-CD3 MAb-coated beads. T cells were 4-fold more sensitive to contact made at the leading edge of the T cell compared with the tail. We conclude that motile T cells are polarized antigen sensors that respond physically to [Ca2+]i signals to stabilize their interaction with APCs.

Analysis of lipopolysaccharide-response genes in B-lineage cells demonstrates that they can have differentiation stage-restricted expression and contain SH2 domains

Bacterial lipopolysaccharide (LPS) is a potent stimulator of B-cell activation, proliferation, and differentiation. We examined the genetic response of B-lineage cells to LPS via trapping of expressed genes with a gene-trap retrovirus. This analysis showed that expression of only a small fraction of genes is altered during LPS stimulation of B-lineage cells. Isolation of the cellular portion of the trapped LPS-response genes via 5' RACE (rapid amplification of cDNA ends) cloning identified novel genes for all the cloned loci. These novel LPS-response genes were also found to have differentiation stage-restricted expression within the B-lymphoid lineage. That LPS-response genes in B cells also have differentiation stage-restricted expression suggests that these genes may be involved in the control of B-cell function and differentiation, since the known members of this class of genes have frequently been found to play a role in the function and differentiation of B-lineage cells. The isolation of novel members of this class of genes, including a gene that contains a putative SH2 domain, will further increase our understanding of the molecular events involved in the control of B-cell differentiation and function.

Enhancement of protein kinase C-dependent O2 production in Epstein-Barr virus-transformed B lymphocytes by p120Ras-GAP antisense oligonucleotide

The mammalian Ras GTPase-activating protein (p120Ras-GAP) interacts with activated members of the Ras superfamily of GTP-binding proteins to accelerate their deactivation by sharply increasing their rates of GTP hydrolysis. Among the Ras-family proteins interacting with p120Ras-GAP is Rap1A/Krev1, whose activity is not affected by p120Ras-GAP but which competes with Ras for p120Ras-GAP. A second protein that interacts with p120Ras-GAP is P190Rac-GAP, which activates the GTPase of guanine nucleotide-binding proteins of the Rho family (including Rac1 and Rac2). Both these p120Ras-GAP-binding proteins are of interest in connection with the regulation of the respiratory burst oxidase, Rap1A/Krev1 because it copurifies with cytochrome b558 and p190Ras-GAP because it inhibits the Rac2-dependent activation of the respiratory burst oxidase in a cell-free system. Using an 18-mer antisense oligonucleotide, we were able to decrease the expression of p120Ras-GAP in Epstein-Barr virus-transformed B lymphocytes. Under conditions where p120Ras-GAP expression was significantly depressed by antisense oligonucleotides, we observed a 40% increase in protein kinase C-dependent but not receptor-dependent O2 production. In contrast, sense and scrambled oligonucleotides had no effect on either p120Ras-GAP expression or O2 production. Our results suggest a role for p120Ras-GAP as a negative regulator in the protein kinase C-mediated activation of the respiratory burst oxidase.

Sos, Vav, and C3G participate in B cell receptor-induced signaling pathways and differentially associate with Shc-Grb2, Crk, and Crk-L adaptors

B cell antigen receptor (BCR)-mediated signal transduction controls B cell proliferation and differentiation. The BCR activates Ras, presumably by the formation of a Shc-Grb2 adaptor complex, which recruits the Grb2-associated guanine nucleotide exchange factor Sos to the plasma membrane. In order to reveal additional BCR-induced signaling events involving the Grb2 adaptor, we undertook the isolation of Grb2-binding proteins. Using the yeast two-hybrid system and bacterial fusion proteins, Vav and C3G were identified as Grb2 binders. Vav is a putative nucleotide exchange factor and a target for BCR-induced tyrosine phosphorylation. C3G exerts nucleotide exchange activity on the Ras-related Rap1 protein. While Sos binds to both Grb2 Src homology-3 (SH3) domains, Vav was found to associate selectively with the carboxyl-terminal SH3 domain, while C3G bound selectively to the amino-terminal SH3 domain of bacterially expressed Grb2. Despite the association of Vav with Grb2 in vitro, we could not demonstrate an interaction between endogenous Vav and Grb2 molecules in primary B cells. Instead, Vav was found to inducibly associate with the Grb2-related adaptor protein Crk upon BCR stimulation. C3G did not bind to either Grb2, Shc, or Crk in vivo. Instead, C3G was found in association with the Crk-L adaptor, both before and after BCR stimulation. We show that Crk-L also participates in BCR signaling, since it inducibly interacts with tyrosine-phosphorylated Cbl. We conclude that, in addition to Sos, Vav and C3G play a role in BCR-mediated signal transduction. These guanine nucleotide exchange factors selectively associate with Grb2, Crk, and Crk-L, respectively, which may serve to direct them to different target molecules. Since Cbl binds to Grb2, Crk, as well as Crk-L, we hypothesize that Cbl may affect the function of all three exchangers.

Lymphocyte homing and homeostasis

The integration and control of systemic immune responses depends on the regulated trafficking of lymphocytes. This lymphocyte "homing" process disperses the immunologic repertoire, directs lymphocyte subsets to the specialized microenvironments that control their differentiation and regulate their survival, and targets immune effector cells to sites of antigenic or microbial invasion. Recent advances reveal that the exquisite specificity of lymphocyte homing is determined by combinatorial "decision processes" involving multistep sequential engagement of adhesion and signaling receptors. These homing-related interactions are seamlessly integrated into the overall interaction of the lymphocyte with its environment and participate directly in the control of lymphocyte function, life-span, and population dynamics. In this article a review of the molecular basis of lymphocyte homing is presented, and mechanisms by which homing physiology regulated the homeostasis of immunologic resources are proposed.

LFA-1 and L-selectin regulation of recirculating lymphocyte tethering and rolling on lung microvascular endothelium

Recirculating lymphocytes migrate into areas of lung inflammation by binding to microvascular endothelium and transmigrating into extravascular tissue. In this report, we examined the multiple-step paradigm using a unique system: recirculating lymphocytes from sheep peripheral lymphatics adhering to activated lung microvascular endothelium in conditions of physiologic flow. Video microscopy demonstrated that recirculating lymphocytes formed abrupt adhesions, without requisite rolling, on the lung microvascular endothelial cells. Lymphocyte velocity was unchanged within 100 ms of the development of firm adhesions. To dissect the adhesion mechanism, the lymphocytes were pretreated with anti-LFA-1 or anti-L-selectin monoclonal antibody (mAb). Both mAb decreased the incidence of firm adhesions. The mechanism of this inhibition was investigated using time-lapse topographic reconstructions of cell movement after pretreatment with mAb. Time-lapse analysis of the movement of lymphocytes pretreated with anti-LFA-1 mAb suggested that abortive adhesion was manifested by a characteristic saltatory movement and a sustained reduction in cell velocity (rolling) to <25 microns/s. In contrast, abortive adhesions of lymphocytes pretreated with anti-L-selectin mAb demonstrated transient arrest (tethering) but minimal rolling before resumption of baseline velocity in the flow stream. These observations provide insights into selectin and integrin regulation of lymphocyte transmigration into the lung. Further, the results of mAb inhibition suggest that the mechanism of lymphocyte migration may have some unique features not observed in studies of neutrophil transmigration.

Induction of costimulatory molecules B7-1 and B7-2 in murine B cells. the CBA/N mouse reveals a role for Bruton's tyrosine kinase in CD40-mediated B7 induction

The binding of CD40 ligand on activated T cells to CD40 on resting B cells induces the expression of costimulatory molecules B7-1 (CD80) and B7-2 (CD86). The induction of B7 molecules by CD40 ligand-CD40 interaction represents a critical step in rendering B cells competent for antigen presentation. The CBA/N mouse has a defect in CD40 signalling which has been attributed to a mutation in Bruton's tyrosine kinase. We have compared the ability of murine CD40 ligand to induce B7-1 and B7-2 expression on B cells isolated from CBA/N and wild-type CBA/J mice. We find that the CBA/N defect partially impairs both B7-1 and B7-2 induction via CD40. Subsequent experiments investigated the roles of different second messenger systems in B7-1 and B7-2 induction in normal B cells. In M12 B lymphomas either CD40 cross-linking or cAMP treatment can induce B7 molecules. Here we report that treatment with dibutyryl-cAMP also induces B7 molecules in normal B cells provided that they have been preactivated by CD40 cross-linking. We also find that PMA and ionomycin treatment of B cells induces B7-2 but not B7-1 expression. Our data therefore show roles for BTK, cAMP and PMA/ionomycin in B7 induction, as well as providing further evidence for differential regulation of B7-1 and B7-2 induction in B cells.

Transcriptional regulation of the Icam-1 gene in antigen receptor- and phorbol ester-stimulated B lymphocytes: role for transcription factor EGR1

Intercellular adhesion molecule (ICAM) 1/CD54 plays an important role in T cell dependent B cell activation and for function of B lymphocytes as antigen-presenting cells. ICAM-1 expression is upregulated as a consequence of B lymphocyte antigen receptor (BCR) signaling, thereby serving to render antigen-stimulated B cells more receptive to T cell-mediated costimulatory signals. We have investigated BCR-induced expression of the Icam-1 gene in primary B cells and B cell lines and have found it to be dependent on BCR-induced expression of the transcription factor EGR1. Icam-1 transcription, induced by BCR cross-linking or bypassing the BCR with phorbol ester, is absent in a B cell line in which the EGR1-encoding gene (egr-1) is methylated and not expressed. A potential EGR1-binding site was located at -701 bp upstream of the murine Icam-1 gene transcription start site and shown by electrophoretic mobility shift assay to bind to murine EGR1. Mutation of this site in the context of 1.1 kb of the Icam-1 promoter significantly abrogated transcriptional induction by phorbol ester and anti-mu stimulation in primary B cells. A direct effect of EGR1 on the Icam-1 promoter is suggested by the ability of EGR1 expressed from an SV40-driven expression vector transactivate the wild-type Icam-1 promoter, whereas mutation of the EGR1 mutation of the EGR1 binding motif at -701 bp markedly compromises this induction. These data identify EGR1 as a signaling intermediate in BCR-stimulated B cell functional responses, specifically linking BCR signal transduction to induction of the Icam-1 gene. Furthermore, similar findings for BCR-induced CD44 gene induction (Maltzman, J.S., J.A. Carman, and J.G. Monroe. 1996. Role of EGR1 in regulation of stimulus-dependent CD44 transcription in B lymphocytes. Mol. Cell. Biol. In press) suggest that EGR1 may be an important signaling molecule for regulating levels of migration and adhesion molecules during humoral immune responses.

Wortmannin-mediated inhibition of phosphatidylinositol 3-kinase activity triggers apoptosis in normal and neoplastic B lymphocytes which are in cell cycle

The B cell functional response following ligation of surface (s) IgM is dependent upon the differentiation stage of the population studied: cross-linking sIgM promotes proliferation of resting tonsillar follicular mantle (FM) B lymphocytes but induces apoptosis in the susceptible Epstein-Barr virus genome-negative Burkitt lymphoma (BL) cell line Ramos (Ramos-BL). This study investigates whether phosphatidylinositol-3-kinase (Pl3-kinase), which has been reported to be intimately involved in the regulation of cellular growth, plays a role in the regulation of these sigpromoted B cell responses, and uses the selective and irreversible inhibitor of Pl3-kinase activity, wortmannin (Wm). In Ramos-BL B cells, at 8 h post-treatment, Wm triggers a transient increase in apoptosis of 16 +/- 6.9% with a concomitant cellular loss of 16 +/- 6.1% from the G1 phase of cell cycle; [3H]thymidine incorporation also decreases by 33 +/- 5.0%, from 37,274 c.p.m. +/- 10% to 25,127 c.p.m. +/- 4.0%. Moreover, at 72 h culture, Wm inhibits anti-IgM-induced FM B lymphocyte levels of [3H]thymidine incorporation typically by 47% and triggers 80% apoptosis from the G0G1 phase of cell cycle. Ramos-BL B cells exhibit high basal levels of Pl3-kinase activity, as determined by immunoprecipitation with antibody to the p85 regulatory subunit of Pl3-kinase and 32P incorporation into phosphatidylinositol, which is not significantly affected by anti-IgM stimulation; by contrast, anti-IgM stimulates significant Pl3-kinase activity over negligible basal levels in FM B lymphocytes. Pre-treatment with Wm inhibits Pl3-kinase activity in both cell types. Taken together these data indicate that in Ramos-BL B cells sigM-triggered growth arrest and apoptosis is Pl3-kinase independent, whereas Pl3-kinase activity is critical for sIgM-triggered mitogenesis of FM B lymphocytes. Thus Pl3-kinase plays a pivotal role in the regulation of both normal and neoplastic B lymphocyte progression through the cell cycle, such that if this Pl3-kinase-dependent pathway is inhibited these cells default to apoptosis.

BCL-2/JH rearrangements in circulating B cells of healthy blood donors and patients with nonmalignant diseases

PURPOSE

To answer the question whether t(14;18)-positive cells can be detected by polymerase chain reaction (PCR) in the peripheral blood of healthy blood donors and patients with nonmalignant diseases.

PATIENTS AND METHODS

Peripheral-blood mononuclear cells (PBMNC) from healthy donors (n = 36) and patients with nonmalignant diseases (n = 21) were examined by two-step PCR for the detection of t(14;18)-positive cells with a breakpoint within the major breakpoint region (MBR). Approximate numbers of t(14;18)-positive cells were determined using limiting dilution assays, as well as the stochastic multiple-tube approach.

RESULTS

We were able to detect t(14;18)-positive cells in PBMNC of approximately 50% of healthy donors and patients with nonmalignant diseases if DNA amounts up to 10 microg were tested. Compared with 17 t(14;18)-positive patients being in complete remission after radiotherapy for low-stage malignant follicular lymphoma, the majority of 26 healthy donors were found to have significantly lower numbers of t(14;18)-positive cells circulating in the peripheral blood. In the case of six healthy donors, more than one t(14;18) DNA fragment based on size and nucleotide sequence analysis was detected. In one healthy individual, four different t(14;18)-positive cell clones were found in nine samples found over 5 years.

CONCLUSION

The occurrence of the t(14;18) translocation is not restricted to follicular lymphoma cells. In healthy donors, long-lived t(14;18)-positive cells can be detected by PCR if the sensitivity is high enough. Based on nucleotide sequence analysis, the t(14;18) DNA fragments detected in healthy donors cannot be distinguished from those found in follicular lymphomas.

Signalling in lymphocyte development

A number of important signal-transduction molecules that regulate lymphocyte maturation and proliferation have been identified. These advances provide a platform for studies on how different signalling events are integrated to generate the required number of lymphocytes with an appropriate antigen receptor repertoire.

Non-stochastic utilization of Ig V region genes in unselected human peripheral B cells

Limited evidence based on a few subjects suggests that human peripheral blood B cells may express a non-stochastic assortment of V region genes. To determine if non-stochastic utilization was a generally applicable rule, the identities of rearranged V region gene segments were determined in unselected peripheral blood B cells from 12 subjects (five male, seven female), ranging in age from 35 to 72 years. The analysis was limited to V region genes belonging to the VH3 gene family. More than 4500 independent VH3-containing rearrangements were analysed. The frequency of occurrence of eight individual VH3 gene segments contained in rearrangements was assessed using gene specific oligonucleotide probes. Usage of elements was not uniform. Three elements, which have been known to encode autoantibodies as well as to be frequently rearranged during fetal development, were represented among rearrangements more frequently than were other members of the VH3 family, and in aggregate, accounted for the majority of rearrangements. These three predominant loci are clustered in an 80 kb region suggesting an influence of chromosomal location on efficiency of rearrangement. The results document a clear, statistically significant, preference for the occurrence of specific V region genes among rearrangements. The modest amount of variation observed between subjects was not associated with either age or gender. Duplications which increased gene dose may have contributed to increased gene usage. These data indicate that, in caucasians, the immunoglobulin rearrangements in adult human B cells are dominated by a few heavy chain V region genes to the exclusion of other putatively equally functional genes. Thus, the conventional notion that the adult repertoire is normalized with respect to family complexity is not confirmed by analysis of individual VH genes.

Signal transduction through the beta1 integrin family surface adhesion molecules VLA-4 and VLA-5 of human B-cell precursors activates CD19 receptor-associated protein-tyrosine kinases

We demonstrate that the CD19 receptor associates with the beta1 family integrin receptors on human B-cell precursors as well as mature B-lymphocytes, and engagement of the beta1 family integrin receptors with monoclonal antibody homoconjugates leads to rapid activation of the CD19-associated protein-tyrosine kinases (PTK) and results in hyperphosphorylation of CD19 on tyrosine residues. Our findings prompt the hypothesis that homoconjugate-induced integrin clustering may effect the approximation and, by intermolecular cross-phosphorylation, activation of the CD19-associated PTK and subsequent tyrosine phosphorylation of the CD19 receptor. The ability of the beta1 family integrin receptors to transmit a biochemical signal triggering the CD19-linked multifunctional PTK pathway provides a possible explanation for the pleiotropic biologic responses generated though adhesive VLA-4- and VLA-5-mediated contacts.

Alternatively spliced exons encode the tissue-specific 5' termini of leukocyte pp52 and stromal cell S37 mRNA isoforms

The pp52 gene encodes an intracellular, F-actin-binding phosphoprotein (also designated LSP1 and WP34) postulated to function in cytoskeleton dynamics and cell motility. We previously reported that different mRNA isoforms are expressed from this gene in cells of the leukocyte lineage versus mesodermally derived cells. These tissue-specific mRNA isoforms are identical except for 5'-untranslated regions and sequences coding for unique N-termini of 23 and 21 amino acids, respectively. As this is a single-copy gene, we predicted that these tissue-specific mRNA isoforms would be generated by alternative RNA splicing. We report that the unique 5' sequences in these mRNA isoforms are encoded in two separate exons containing ATG initiation codons. These features confirm that the pp52 and S37 mRNA isoforms are generated by alternative RNA splicing and establish that they are independently translated. Other results presented here indicate that the differential expression of these exons in leukocytes versus mesodermally derived cells is regulated at the level of transcription by tissue-specific promoters.

Emerging concepts regarding B cells and autoantibodies in murine lupus nephritis. B cells have multiple roles; all autoantibodies are not equal

Despite observations linking the severity of lupus nephritis to the quantity and location of glomerular immune deposits, it had been difficult to decipher the primary role of B cells and autoantibodies in this process. Newer technologies have provided the means to evaluate the roles of whole B cell populations and individual immunoglobulins in lupus lesions. In this review, recent advances in this area are summarized, with particular emphasis on work from the authors' laboratories. The results implicate a primary role for B cells and immunoglobulins in lupus nephritis, including glomerular, interstitial, and vascular lesions. Multiple antibody-ligand interactions participate in glomerular immune deposit formation in individuals with lupus nephritis. Recent evidence suggests that in situ formation of immune deposits by either cross-reactivity of autoantibodies with intrinsic glomerular antigens (i.e., anti-DNA antibodies with laminin) or direct interaction of autoantibodies with circulating autoantigens lodged within glomeruli (i.e., anti-DNA antibodies with histone/DNA). The predominant autoantibody-glomerular antigen interaction(s) in a given individual influences the principal location of immune deposition, which in turn influences the pathologic and clinical expression of disease. It is believed that these phenomena contribute to the phenotypic diversity commonly observed among individuals with lupus nephritis. Furthermore, these consequences are dependent on properties unique to both subsets of lupus autoantibodies and to their target antigen ligands within the glomerulus. Thus, the autoantibody variable or antigen binding region, along with the nature and location of the target glomerular antigen (or site of circulating antigen deposition), are influential in initiating these perturbations.

Human-->mouse radiation chimera do not develop Epstein-Barr virus lymphoma

It has been shown that engraftment of human peripheral blood lymphocytes (PBL) from Epstein-Barr virus (EBV) seropositive donors in C.B-17/SCID mice is associated with a high incidence of human B cell tumors. More recently, we described a new approach enabling engraftment of human PBL in normal strains of mice or rats receiving lethal split-dose radiation and radioprotected with SCID bone marrow. We now demonstrate that, in contrast to SCID recipients of human PBL, Balb/c and C3H/HeJ recipients of 50-100 x 10(6) human PBL did not develop any EBV lymphoma during a 7-month follow-up period, but were successfully engrafted with human B and T cells. On the other hand, lymphoma developed in 90% of the C.B-17/SCID mice infused with 70 x 10(6) human PBL from the same donor. Likewise, 36% of beige/nude/xid (BNX) mice, exposed to 12 Gy TBI, radioprotected with SCID bone marrow and then transplanted with human PBL developed lymphoma. Similar results were obtained when different strains were infused with PBL of the same donor. Immunohistochemical analysis indicated that the tumor cells were of human B cell origin and expressed the EBV-encoded latent membrane protein-1 and nuclear antigen 2. While further studies are required to understand the mechanisms which suppressed outgrowth of EBV lymphoma in human --> mouse radiation chimera, compared to human --> C.B-17/SCID or human --> BNX chimera, this marked resistance offers new possibilities for transplantation of hematopoietic tissues or cells from EBV-positive donors.

Cooperation of tyrosine kinases p72syk and p53/56lyn regulates calcium mobilization in chicken B cell oxidant stress signaling

A chicken B cell line DT40 and its syk-negative or lyn-negative mutants were used to investigate the roles of protein-tyrosine kinases in oxidant stress signaling. The data presented here for wild-type cells demonstrate that hydrogen peroxide stimulates p53/56lyn-dependent tyrosine phosphorylation and activation of p72syk, and induces a rapid and prolonged elevation of intracellular calcium, which consists of calcium release from intracellular stores and influx from the extracellular space. Hydrogen-peroxide-triggered calcium mobilization was impaired in both syk-negative and lyn-negative cells, which was mainly due to the loss of calcium release from intracellular stores. Further studies indicated that inositol trisphosphate production was also abolished in both syk-negative and lyn-negative cells, which is consistent with the loss of calcium release. Taken together, these observations suggest that the defect of p72syk or p53/56lyn was responsible for the abnormality of calcium mobilization in both lyn-negative and syk-negative cells, and that both p72syk and p53/56lyn might regulate calcium mobilization through the phosphatidylinositol pathway in B cell oxidant stress signaling.

Autoimmunity in the peripheral nervous system

The PNS is an immunocompetent organ. The participating cellular and humoral elements in the local immune circuitry have been identified. The model disorder EAN is extensively being used to examine the induction, amplification and effector phase of autoimmune responses to peripheral nerve antigens (Figure 9). Potential autoantigens contained in the myelin sheath and on the axolemma have been characterized. Recent years have seen a rapid growth of information concerning the pathogenesis of the Guillain-Barré syndrome, which has turned out to be a heterogeneous disorder, both in clinical characteristics, course and prognosis, and in the underlying pathology. It can be anticipated that using the better understanding of principal mechanisms of autoimmunity in the PNS will aid in the development of more specific and efficacious treatments.

Regulation of B cell function by the immunosuppressive agent leflunomide

Leflunomide is an immunosuppressive drug capable of inhibiting cellular and humoral mediated responses in vivo. The mechanism responsible for suppression of B cell antibody responses in vivo has not been identified. In this study we demonstrate that leflunomide functions to inhibit murine B cell antibody production by directly acting on the B cell. Experiments performed in vivo showed that both T cell-dependent as well as T cell-independent antigen responses were suppressed by leflunomide. Initial in vitro experiments demonstrated that leflunomide inhibited B cell antibody production by decreasing B cell proliferation. The suppression of B cell proliferation induced by a variety of stimuli that use different signal cascade components suggested that leflunomide was acting on a common component required for B cell proliferation. Kinetic studies with LPS activated B cells revealed that leflunomide retained its inhibitory activity when added as late as 24 hr after stimulation in an 88-hr assay. By analyzing the cell cycle of LPS-stimulated B cells we observed that leflunomide targets two different stages in cell cycle transition: (1) from G1 to S phase and (2) from S phase to G2/M phase. Analysis of one of the cyclin-dependent kinases, Cdk2 protein, by Western blot revealed that Cdk2 levels were decreased, in the presence of leflunomide, 48 hr after stimulation. These data further confirmed that leflunomide inhibited B cell progression through the S phase. We also present evidence that the addition of exogenous uridine reversed the antiproliferative activity of leflunomide. This indicated that leflunomide acted as a pyrimidine synthesis inhibitor, thereby inhibiting B cell proliferation and cell cycle progression.

Relation of size at birth to non-insulin dependent diabetes and insulin concentrations in men aged 50-60 years

OBJECTIVE

To establish whether the relation between size at birth and non-insulin dependent diabetes is mediated through impaired beta cell function or insulin resistance.

DESIGN

Cohort study.

SETTING

Uppsala, Sweden.

SUBJECTS

1333 men whose birth records were traced from a cohort of 2322 men born during 1920-4 and resident in Uppsala in 1970.

MAIN OUTCOME MEASURES

Intravenous glucose tolerance test at age 50 years and non-insulin dependent diabetes at age 60 years.

RESULTS

There was a weak inverse correlation (r=-0.07, P=0.03) between ponderal index at birth and 60 minute insulin concentrations in the intravenous glucose tolerance test at age 50 years. This association was stronger (r=-0.19, P=0.001) in the highest third of the distribution of body mass index than in the other two thirds (P=0.01 for the interaction between ponderal index and the body mass index). Prevalence of diabetes at age 60 years was 8% in men whose birth weight was less than 3250 g compared with 5% in men with birth weight 3250 g or more (P=0.08; 95% confidence interval for difference -0.3% to 6.8%). There was a stronger association between diabetes and ponderal index: prevalence of diabetes was 12% in the lowest fifth of ponderal index compared with 4% in the other four fifths (P=0.001; 3.0% to 12.6%).

CONCLUSION

These results confirm that reduced fetal growth is associated with increased risk of diabetes and suggest a specific association with thinness at birth. This relation seems to be mediated through insulin resistance rather than through impaired beta cell function and to depend on an interaction with obesity in adult life.

Role of Rho in chemoattractant-activated leukocyte adhesion through integrins

Heterotrimeric guanine nucleotide binding protein (G protein)-linked receptors of the chemoattractant subfamily can trigger adhesion through leukocyte integrins, and in this role they are thought to regulate immune cell-cell interactions and trafficking. In lymphoid cells transfected with formyl peptide or interleukin-8 receptors, agonist stimulation activated nucleotide exchange on the small guanosine triphosphate-binding protein RhoA in seconds. Inactivation of Rho by C3 transferase exoenzyme blocked agonist-induced lymphocyte alpha4beta1 adhesion to vascular cell adhesion molecule-1 and neutrophil beta2 integrin adhesion to fibrinogen. These findings suggest that Rho participates in signaling from chemoattractant receptors to trigger rapid adhesion in leukocytes.

p120cbl is a major substrate of tyrosine phosphorylation upon B cell antigen receptor stimulation and interacts in vivo with Fyn and Syk tyrosine kinases, Grb2 and Shc adaptors, and the p85 subunit of phosphatidylinositol 3-kinase

We and others have demonstrated that the c-cbl proto-oncogene product is one of the earliest targets of tyrosine phosphorylation upon T cell receptor stimulation. Given the similarities in the B and T lymphocyte antigen receptors, and the induction of pre-B leukemias in mice by the v-cbl oncogene, we examined the potential involvement of Cbl in B cell receptor signaling. We demonstrate prominent and early tyrosine phosphorylation of Cbl upon stimulation of human B cell lines through surface IgM. Cbl was associated in vivo with Fyn and, to a lesser extent, other Src family kinases. B cell activation also induced a prominent association of Cbl with Syk tyrosine kinase. A substantial fraction of Cbl was constitutively associated with Grb2 and this interaction was mediated by Grb2 SH3 domains. Tyrosine-phosphorylated Shc, which prominently associated with Grb2, was detected in association with Cbl in activated B cells. Thus, Grb2 and Shc adaptors, which associate with immunoreceptor tyrosine based activation motifs, may link Cbl to the B cell receptor. B cell activation also induced a prominent association between Cbl and the p85 subunit of phosphatidylinositol (PI) 3-kinase resulting in the association of a substantial fraction of PI 3-kinase activity with Cbl. Thus, Cbl is likely to play an important role to couple the B cell receptor to the PI 3-kinase pathway. Our results strongly suggest a role for p120cbl in signaling downstream of the B cell receptor and support the idea that Cbl participates in a general signal transduction function downstream of the immune cell surface receptors.

The Fas antigen is detected on immature B cells and the representative cell lines show Fas-mediated apoptosis

The expression and functions of Fas antigen, a major regulator of apoptosis, in T-cell selection have been intensively investigated, but little is known about its expression i immature B cells which are also selected in the bone marrow, and plasma cells which are at the terminal stage of B-cell differentiation and are designed to die. We examined bone marrow cells and found Fas antigen on these cells at low levels. Next we analysed Fas expression and susceptibility to anti-Fas antibody-mediated apoptosis on B-cell lines representing various stages of differentiation. We also examined the expression of Bcl-2 and Bax on these lines, which were intimately related to apoptosis. Fas antigen was almost negative on pre-pre-B cell lines and was detected on pre-B-cell lines at low levels. All plasma cell lines expressed Fas at a low to moderate level. Some cell lines with peripheral B-cell phenotype expressed Fas antigen. Except for the Burkitt cell lines and one plasma cell line, susceptibility to Fas-mediated apoptosis depended on Fas expression. Bcl-protein was detected on all but one cell line and Bax was detected on 15/23 lines, but neither were related to cellular differentiation or Fas expression.

Generation and function of natural self-reactive B lymphocytes

To study the significance of developmentally restricted VH gene expression, and natural self-reactive B lymphocytes, VH81X-mu-heavy chain transgenic mice were constructed and the expression of this gene analysed at different stages of development and in different B-cell subsets. It was found that the majority of B cells expressed the transgenic heavy chain associated with different kappa but not lambda light chains. These B cells were predominantly self reactive and distributed normally to peripheral lymphoid organs. Among the CD23-/IgMhi B cells of transgenic mice there was a population of clonally unrelated relatively self-reactive B cells that expressed identical antigen receptors but did not secrete antibody. Continued administration of antibody of the same specificity during post-natal development reduced the generation of these B cells to very low levels. These studies show that although natural self-reactive B cells are continuously generated as a result of positive selection by self-antigen, their maturation may be blocked at the CD23-/IgMhi stage. Their failure to enter the CD23+ IgMlo B cell pool may prevent them from receiving T-cell help and production of high affinity potentially pathogenic autoreactive IgG antibodies.