Myo1g is required for efficient adhesion and migration of activated B lymphocytes to inguinal lymph nodes

Cell migration is a dynamic process that involves adhesion molecules and the deformation of the moving cell that depends on cytoskeletal remodeling and actin-modulating proteins such as myosins. In this work, we analyzed the role of the class I Myosin-1 g (Myo1g) in migratory processes of LPS + IL-4 activated B lymphocytes in vivo and in vitro. In vivo, the absence of Myo1g reduced homing of activated B lymphocytes into the inguinal lymph node. Using microchannel chambers and morphology analysis, we found that the lack of Myo1g caused adhesion and chemotaxis defects. Additionally, deficiency in Myo1g causes flaws in adopting a migratory morphology. Our results highlight the importance of Myo1g during B cell migration.

Low percentages of regulatory T cells in common variable immunodeficiency (CVID) patients with autoimmune diseases and its association with increased numbers of CD4+CD45RO+ T and CD21low B cells

BACKGROUND

Common variable immunodeficiency (CVID) is a heterogeneous group of primary antibody deficiencies defined by marked reductions in serum IgG, IgA and/or IgM levels and recurrent bacterial infections. Some patients are associated with defects in T cells and regulatory T cells (Tregs), resulting in recurrent viral infections and early-onset autoimmune disease.

METHODS

We analyzed whether there is an association between Tregs cells (CD4+CD25+CD127^low and CD4+CD25+FoxP3+); memory T cells (CD4+CD45RO+); memory B cells (CD19+CD27-IgD-); and CD21^low B cells (CD19+CD38^lowCD21^low); as well as autoimmune manifestations in 36 patients with CVID (25 women and 11 men, mean age 24 years), all by flow cytometry.

RESULTS

Fourteen patients presented with autoimmune diseases (AI) (39%), including 11 with autoimmune thrombocytopenia (ITP) (31%); two with vitiligo (6%); one with systemic lupus erythematosus (LES) (3%); and one with multiple sclerosis (MS) (3%). CVID patients with AI had a reduced proportion of Tregs (both CD4+CD25+CD127^low and FoxP3+ cells) compared with healthy controls. CVID patients with AI had expanded CD21^low B cell populations compared with patients who did not have AI. A correlation between increased CD4+CD45RO T cell populations and reduced Tregs was also observed.

CONCLUSIONS

Our results showed that 39% of patients with CVID had AI and reduced Tregs populations. Research in this area might provide noteworthy data to better understand immune dysfunction and dysregulation related to CVID.

Tspan33 is Expressed in Transitional and Memory B Cells, but is not Responsible for High ADAM10 Expression

Tetraspanins are a family of transmembrane proteins that form membrane microdomains. They play important roles in migration, adhesion and other cellular processes. TspanC8, a subfamily of tetraspanins, was found to associate and promote ADAM10 trafficking and cell surface localization. One of its members, Tspan33, is expressed in activated B cells. Using RT-PCR and flow cytometry, we analysed the pattern of expression of Tspan33 in B cells from healthy donors. We found Tspan33 expression in early and late stages of B cell development. However, Tspan33 expression did not correlate with ADAM10 surface expression. We also found expression of Tspan33 early in the activation process. Given its predominant expression in activated B cells and in several lymphomas, but not in naive B cells, we hypothesize that Tspan33 could be a potential target for therapeutic purposes.

Variations of B cell subpopulations in peripheral blood of healthy Mexican population according to age: Relevance for diagnosis of primary immunodeficiencies

BACKGROUND

Peripheral blood B cells include lymphocytes at various stages of differentiation, each with a specific function in the immune response. All these stages show variations in percentage and absolute number throughout human life. The numbers and proportions of B subpopulation are influenced by factors such as gender, age, ethnicity, and lifestyle. This study establishes reference values according to age of peripheral blood B cell subtypes in healthy Mexican population.

METHODS

Peripheral blood from healthy new-borns and adults were analysed for total B cell subpopulations, using surface markers such as CD19, IgM, IgD, CD21, CD24, CD27, and CD38, to identify naïve, memory with and without isotype switch, double-negative, transitional, and plasmablast cells.

RESULTS

We observed a significant variation in terms of frequency and absolute counts between all groups analysed. Values from each B cell subpopulation show variations according to age.

CONCLUSIONS

In order to attempt to elucidate reference values for B cell subpopulation, the present study evaluated a population sample of healthy blood donors from this region. Values reported here can also be used as a tool for diagnosis of diseases in which B cell maturation is affected.

Functional characterization of two new STAT3 mutations associated with hyper-IgE syndrome in a Mexican cohort

Hyper-IgE syndrome (HIES) is an immunodeficiency disorder that is characterized by distinctive immunologic and non-immunologic manifestations. Although mutations in signal transducer and activator of transcription 3 (STAT3) have been associated with HIES, the exact nature of the relationship is unknown. Here, we characterized the functional activity of STAT3 and its mutations in 11 Mexican patients with autosomal dominant HIES. STAT3 phosphorylation was evaluated by flow cytometry, and in silico analyses were performed to estimate the impact of allelic mutations on the DNA binding and SH2 domains of the STAT3 protein. Electrophoretic mobility shift assays were used to assess whether the STAT3 mutants could bind to the consensus oligonucleotide target in vitro. Two novel mutations [g.58891A>T (Asn395Tyr) and g.59078A>T (Asn425Tyr)] as well as one possible somatic mosaicism were found in several of the patients who bore some remarkable features. However, there were no direct correlations between genotypes and HIES clinical features. STAT3 phosphorylation was found to be lower in the patient cohort than in healthy controls. Moreover, the mutated STAT3 proteins could bind to the Sp1, but not to the STAT3, consensus sequence. From these functional studies, the STAT3 mutations found in our patient cohort were concluded to be deleterious for normal STAT3 function.

Molecular analysis for patients with IL-12 receptor β1 deficiency

Autosomal recessive interleukin-12 receptor β1 (IL-12Rβ1) deficiency has been described as the most common cause of Mendelian susceptibility to mycobacterial disease (MSMD), characterized by clinical disease due to weakly virulent mycobacteria such as Bacille Calmette-Guérin (BCG) vaccines and environmental mycobacteria (EM) in children who are normally resistant to most infectious agents. Here, we report the cases of five patients with mycobacterial infection, including one with systemic lupus erythematosus (SLE). Blood samples from patients and healthy controls were activated in vitro with BCG, BCG+IL-12, and BCG+IFN-γ. The results showed reduced or no production of IFN-γ after IL-12 stimulation in all samples. IL-12Rβ1 expression on the cell surface was negligible or absent. Genetic analysis showed five novel mutations.

Analysis of antibody response in human dengue patients from the Mexican coast using recombinant antigens

This study was undertaken to evaluate the feasibility of using recombinant dengue proteins to discriminate between acute dengue infections versus uninfected dengue samples. Dengue virus proteins E, NS1, NS3, and NS4B were cloned as fusion proteins and expressed in Escherichia coli. Recombinant products were tested in 100 serum samples obtained from acute dengue fever cases collected from 3 states of Mexico where dengue is endemic. Sera from 75 healthy individuals living in nonendemic areas for dengue were used as a control group. In sera from the dengue patients group, antibody responses to E protein were demonstrated in 91% of cases and NS1 protein was recognized to various extents (99%) within the first 7 days of infection. The antibody responses to NS3 and NS4B were frequently of low magnitude. Consistent negative antibody responses to all proteins were found in sera from the control group. These data suggest that the glutathione-S-transferase (GST)-dengue fusion proteins may be feasible antigens for a sensitive and specific serological assay.

Characterization of Bruton's tyrosine kinase mutations in Mexican patients with X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is a humoral primary immunodeficiency in which affected patients have very low levels of peripheral B cells and a profound deficiency of all immunoglobulin isotypes. Mutations in the gene encoding for Bruton's tyrosine kinase (Btk) are responsible for most of the agammaglobulinemia. In this work, 14 Btk mutations responsible of causing XLA are described; eight of which are novel and six are mutations previously reported. Seven of the mutations were due to deletions and insertions of exons and introns, respectively, which suggest splicing defects. The others were missense mutations, five of which affect arginine residues and have been described, and two new which affect leucine and glutamine residues (L111P and E605G). Most of these mutations were located at the kinase domain of Btk and, less frequently, they were found in PH and SH2 domains. Protein expression was also affected since most of the patients did not express or express very low Btk.

A fusogenic peptide expressed on the surface of Salmonella enterica elicits CTL responses to a dengue virus epitope

Attenuated Salmonella strains are used widely as live carriers of antigens because they elicit both mucosal and systemic immunity against passenger antigens. However, they generally evoke poor cytotoxic T cell (CTL) responses because Salmonella resides within vacuolar compartments and the passenger antigens must travel to the cytosol and be processed through the MHC class I-dependent pathway to simulate CTLs. To address this problem, we designed a fusion protein to destabilize the phagosome membrane and allow a dengue epitope to reach the cytosol. The fusion protein was displayed on the bacterial surface of Salmonella enterica serovar Typhimurium SL3261 through the beta domain of the autotransporter MisL. The passenger alpha domain contained, from the N-terminus, a fusogenic sequence, the NS3 protein 298-306-amino acid CTL epitope from the dengue virus type 2, a molecular tag, and a recognition site for the protease OmpT to release it to the milieu. Display of the fusion protein on the bacterial surface was demonstrated by IFA and flow cytometry using antibodies against the molecular tag. Cleavage of the fusogenic protein-dengue peptide was demonstrated by flow cytometry using OmpT+ Escherichia coli strains. The recombinant Salmonella strains displaying the fusogenic-dengue peptide were able to lyse erythrocytes, induced specific proliferative responses, and elicited CTL responses. These results suggest that the recombinant fusion proteins containing fusogenic sequences provide a promising system to induce CTLs by live vector vaccines.

Production and characterization of a monoclonal antibody specific for NS3 protease and the ATPase region of Dengue-2 virus

Dengue is considered a reemerging disease of worldwide distribution. The Dengue virus non-structural protein 3 (NS3) is known to possess ATPase, helicase, and protease activities that are a constitutive part of the replication complex of Dengue virus. In this report, we discuss the cloning, expressing, and purifying of the Dengue-2 NS3 protein, to immunize mice and then generate monoclonal antibodies (MAbs). Our results show the production of MAbs specific to NS3 protein of Dengue-2 virus, which by immunofluorescence recognize the native protein in experimentally infected endothelial cells (HMEC). Likewise, C6/36-infected lisates were used in Western blots, and observed the specific characteristic band that defines the NS3 protein. We conclude that these antibodies may be a useful tool, not only to study the replicative process of Dengue virus, but also to generate specific diagnostic tools for Dengue infection.

Expression and function of CD22, a B-cell restricted molecule

In this work, we studied the expression and function of CD22 in murine B cells. CD22 has been previously characterized as an activation marker of mature B lymphocytes. However, we found that CD22 is expressed early during the ontogeny of B cells in the bone marrow and spleen, and was found on B cells isolated from all the different lymphoid compartments. We also found that B cells stimulated through the B-cell antigen receptor (BCR), CD38 and CD40, upregulated CD22 expression to maximal levels within 24 h after stimulation, but that the levels of CD22 declined at later times (48 and 72 h). CD22 is rapidly phosphorylated after BCR signal transduction, and is believed to downregulate B-cell activation. In this study, we did not detect CD22 phosphorylation in activated B cells after CD38 or CD40 cross-linking, even though CD22 was clearly phosphorylated in the BCR-stimulated B cells. Consistent with this, we found no evidence of physical association between CD38 or CD40 and CD22 in B cells. The lack of association or phosphorylation of CD22 induced by CD38 and CD40 cross-linking indicates that CD22 may not downregulate the activation induced by these two molecules.

Enforced and prolonged CD40 ligand expression triggers autoantibody production in vivo

CD40, a glycoprotein expressed on B lymphocytes plays an important role in B cell development, growth and differentiation. The ligand for the CD40 is a 39-kDa glycoprotein (CD154) expressed on the surface of activated T lymphocytes and is essential for thymus-dependent humoral immunity. The expression of CD154 is tightly regulated and its transient expression reduces the chances of potentially deleterious bystander activation of B cells. Stimulation through CD40 has been studied in vitro by using antibodies against CD40, by membranes of activated T cells or lately, by CD154 transfected cells. In this work we have evaluated the outcome of CD40-CD40 ligand interaction in vitro and in vivo by using CD154-transfected L929 cells. In vitro assays showed that CD154-L929 cells can induce on B cells: IL-4-dependent proliferation, up-regulation of CD23, CD54 and class II molecules and can also rescue WEHI-231 B cell lymphoma from anti-IgM-induced apoptosis. Interestingly, in vivo assays revealed that when CD154-L929 cells were inoculated into the spleen, mice developed a strong but transient production of anti-erythrocyte autoantibodies. Through B lymphocyte activation with CD154-transfected L929 cells both in vitro and in vivo, our data reveal that enforced and prolonged expression of CD40 ligand overcomes the tightly regulated mechanisms of B cell activation, triggering the production of autoantibodies. This system might be used to evaluate the early steps of an autoimmune response and the role of CD40-CD154 in the induction of primary responses in vivo.

CD45R, CD44 and MHC class II are signaling molecules for the cytoskeleton-dependent induction of dendrites and motility in activated B cells

Anti-CD44 or anti-MHC II antibodies bound to tissue culture plates have previously been shown to induce a dramatic generation of dendritic processes in activated murine B cells. In this study, we demonstrate a similar generation of dendrites and cell motility in activated B cells through CD45R. The dynamic formation of dendritic processes and associated induction of cell motility were analyzed by video microscopy and were characterized by a rapid, and multidirectional emission of dendrites with retractile behavior. The addition of cytochalasin E totally blocked dendrites formation and motility induced through either CD45R, CD44 or MHC II, suggesting that the necessary cytoskeletal rearrangements require active polymerization of actin. Confocal microscopy showed an accumulation of F-actin in the dendrites, as long as cells were elongating. In contrast, G-actin was localized in the perinuclear area and also accumulated in sites where dendrites originated. Preincubation of B cells with staurosporine (a PKC inhibitor) or BAPTA-AM (a calcium chelator) prevented these morphological changes, indicating additionally a requirement for a PKC-calcium-dependent activity. Dendrite formation and cellular motility, therefore, seem to be two manifestations of the same phenomenon, and CD44, CD45R and MHC II appear to be signaling molecules for the observed cytoskeleton-dependent morphological changes.

Cell surface expression of CD154 inhibits alloantibody responses: A mechanism for the prevention of autoimmune responses against activated T cells?

Binding of CD40 by CD154 expressed on activated T cells is a pivotal event in T cell help to B cells, macrophages, and other antigen-presenting cells. Expression of CD154 by MHC mismatched cells, in contrast to expectations, strongly suppressed alloantibody responses against the cells. This was caused by a failure of priming of antibody responses by the CD154 expressing cells. We hypothesize that this lack of response against CD154 expressing cells may represent a mechanism that has evolved to prevent autoantibody responses being generated against the CD154 antigen itself, as B cells expressing antibody reactive with CD154 would probably escape deletion on binding antigen in the bone marrow due to rescue by the simultaneous ligation of CD40.

Arrest of B lymphocyte terminal differentiation by CD40 signaling: mechanism for lack of antibody-secreting cells in germinal centers

Despite extensive research, the role of CD40 signaling in B cell terminal differentiation remains controversial. Here we show that CD40 engagement arrests B cell differentiation prior to plasma cell formation. This arrest is manifested at a molecular level as a reduction in mRNA levels of secretory immunoglobulin gene products such as mu(s) and J chain as well as the loss of the transcriptional regulator BLIMP-1. Furthermore, the inhibition of B cell differentiation by CD40 engagement could not be overcome by either mitogens or cytokines, but could be reversed by antibodies that interfere with the CD40/gp39 interaction. These data suggest that secretory immunoglobulin is not produced by B cells that are actively engaged by gp39-expressing T cells.

CD44-stimulated dendrite formation ('spreading') in activated B cells

A rat monoclonal antibody (mAb) (NIM-R8), insolubilized by binding to plastic plates, induced a rapid and extensive formation of dendrite processes ('spreading') in B lymphocytes activated by anti-IgM and interleukin-4 (IL-4) or anti-CD38 and IL-4. In contrast, resting B cells were unable to spread similarly on the NIM-R8-coated plates. The NIM-R8 antibody recognized a 90,000 MW surface glycoprotein (gp90) present on both B and T lymphocytes. The expression of this molecule was greatly increased after polyclonal (lipopolysaccharide, anti-IgM plus IL-4 or concanavalin A) activation. The NIM-R8 mAb with or without IL-2 or IL-4 was unable to induce proliferation of splenic lymphocytes. Following the demonstration that the NIM-R8 mAb recognizes the murine equivalent of human CD44, the induction of spreading of activated B lymphocytes was studied using a panel of mAb recognizing different epitopes of murine CD44. All of these different mAb induced similar spreading of activated B cells. The ligand-inducible spreading of activated B lymphocytes may be an important mechanism for providing an increased cell-surface area for cell-cell or cell-matrix interactions, and thus may be an important factor controlling the response of activated lymphocytes.

Evolution of lymphocyte populations in armadillos (Dasypus novemcinctus) inoculated with M. leprae

In human leprosy patients there are changes in the percentages of T and B lymphocytes in peripheral blood, and there is a correlation with the clinical characteristics or manifestations of the disease. These phenomena still require clarification regarding the triggering mechanism involved that may lead to one or the other clinical entities. Much has yet to be learned about the intricacies of whether the changes in subpopulations of T and B lymphocytes are a causative factor or an effect attributable to the microorganism itself. The armadillo is an excellent animal model to study how Mycobacterium leprae spread, turning into an established infection. The application of modifications in percentages of the subpopulations of B and T lymphocytes in armadillos may well lead to extrapolation of the results obtained in this animal model in an attempt to be able to manipulate the course of the disease in humans. The purpose of the study was to evaluate changes in the percentages of rosette-forming and sIgM+ mononuclear cells during a full year in groups of armadillos: five randomly chosen animals formed the control group and 11 armadillos were inoculated with M. leprae obtained from a human leproma at the onset of the 12-month period of the study. Of the 11 randomly selected armadillos that were inoculated, only five developed an active and disseminated infection. The percentage of rosette-forming cells did not show statistically significant variations during the first 6 months of the study. However, at months 8 and 12 a significant increment in this parameter was observed (p < 0.05) in the animals with active infection. In regard to the variations in the numbers of sIgM+ cells, significant changes occurred in the armadillos with active infection at month 2. However, results returned to normal and no changes were seen at later times. No significant changes occurred in the group of animals inoculated but not developing active infection compared with the other groups. The results are considered sufficiently interesting to encourage further study on the cell-mediated immune system of the armadillo and the changes that occur during the development and dissemination of an inoculated infection with M. leprae. Since this mammal is of great value as an effective animal model in the experimental research of M. leprae, there is an urgent need to obtain, as quickly as possible, a thorough understanding of the cellular branch of its immune system and, thereby, be in a position to extrapolate immune modulation to benefit human leprosy patients.

Immune response of armadillos (Dasypus novemcinctus). I. Use of lectins to identify lymphocyte subpopulations and to evaluate cell proliferation

Lectins have been used to study populations and discrete differentiation stages of lymphocytes. Likewise, lectins have been of practical importance in promoting mitogenic stimulation of lymphocytes in numerous species. In this research project, we took advantage of these tools in an attempt to identify specific subsets of peripheral blood lymphocytes obtained from healthy nine-banded armadillos (Dasypus novemcinctus). The same cell source served to evaluate mitogenic stimulation. Twelve FITC-labeled lectins were used; 5 (ConA, LcH, RCA, WGA and UEA) reacted with almost 100% of the lymphocytes and 7 (PNA, DBA, SBA, PCA, PHA-L, PWM and VVA) recognized variable percentages (< 100% of these cells). This latter group of lectins may be useful in the identification of armadillo lymphocyte subsets, or may correlate with discrete stages of differentiation of these cells. The same lectins served to evaluate mitogenic stimulation in an aliquot of the same peripheral blood mononuclear cells. Of the 12 lectins studied, 5 (ConA, PHA-L, PWM, DBA and SBA) had the capacity to induce mitogenic stimulation in the whole mixture of mononuclear cells, giving rise to variable degrees in the corresponding mitogenic index obtained for each of the 5 lectins. Those lectins that gave an indication of selective identification of lymphocytes, that is, the percentages at or below 75%, may prove useful in the evaluation of the immune response of healthy armadillos as well as the evolution of progression stages of lepromatous leprosy in armadillos inoculated with the same strain of Mycobacterium leprae that affects humans.

Identification and purification of armadillo (Dasypus novemcinctus) immunoglobulins: preparation of specific antisera to evaluate the immune response in these animals

In this work we describe the purification and characterization of armadillo immunoglobulins. The IgM was precipitated using low-strength ionic solution and further purified by filtration through Sephadex G-200. The IgG was obtained in pure form by precipitation of serum with ammonium sulfate and DEAE-cellulose ion exchange chromatography. The purity of these immunoglobulins was evaluated by polyacrylamide gel electrophoresis. The results showed 28-kDa light chains and 55-kDa and 70-kDa heavy chains for IgG and IgM, respectively. The rabbit antibodies against these molecules were used to prepare fluorescein (FITC) and peroxidase conjugates. The FITC conjugate was used to quantify IgM-bearing lymphocytes. An average of 17% of peripheral blood lymphocytes were sIgM+ from 14 healthy animals. Additionally, in the same animals we quantified lymphocytes with the capacity to form rosettes with sheep red-blood cells; the average for this marker was 10%. Also, the production of crossreacting antibodies to BCG was evaluated in healthy and Mycobacterium leprae-inoculated animals using the peroxidase conjugates. All animals with active infection recognized BCG antigens.

CD38 unresponsiveness of xid B cells implicates Bruton's tyrosine kinase (btk) as a regular of CD38 induced signal transduction

CD38 is a 42 kDa membrane-associated ectoenzyme expressed by a large proportion of human and mouse lymphocytes. Agonistic antibodies to CD38 induce a strong proliferative response in lymphocytes additionally co-stimulated with other growth co-factors such as IL-4, IL-2 plus accessory cells or sub-mitogenic doses of endotoxin. We show here that B lymphocytes from unstimulated X-linked immunodeficient (xid) mice are unresponsive to CD38 stimulation, both in terms of proliferative response and surface antigen modulation. This CD38 unresponsiveness is evident in the presence of excess quantities of, and normal responses to, the accessory growth co-stimulants required for this response. CD38 molecules expressed on xid B cells are normal in terms of expression levels, size and enzymatic activity, suggesting that CD38 unresponsiveness reflects a down-stream signaling defect. In light of the recent proposal that the xid gene encodes a tyrosine kinase called Bruton's tyrosine kinase (btk), these data suggest that btk is either an integral component or an indirect regulator of the CD38-induced signal transduction pathway.

CD38 expression on mouse T cells: CD38 defines functionally distinct subsets of alpha beta TCR+CD4-CD8- thymocytes

We have examined CD38 expression on mouse lymphocytes using the rat mAb NIM-R5 and demonstrate that CD38 expression is restricted to approximately 8% of thymocytes. Although CD38 is absent from the majority of CD4+CD8- and CD4-CD8+ T cells, we detected a strong correlation between CD38 expression and alpha beta+CD4-CD8- T cells in the thymus, with nearly 80% of alpha beta TCR+CD4-CD8- thymocytes being CD38+. Using heat stable antigen (HSA) and CD38, we divided alpha beta+CD4-CD8- thymocytes into four subsets: HSA+CD38-, HSA-CD38hi, HSA-CD38low and HSA-CD38-. Two established characteristics of alpha beta TCR+CD4-CD8- cells, bias towards V beta 8.2 TCR expression and high levels of IL-4 production, were used to establish a possible relationship between the above thymocyte subsets. Our present data show that the HSA+CD38- subset is not biased towards V beta 8.2 TCR expression whereas the HSA-CD38- subset does show this bias (approximately 47%). Neither of these subsets make IL-4 upon CD3 mediated stimulation. In contrast, the CD38+ subsets are heavily biased toward V beta 8.2 expression and produce large amounts of IL-4 upon stimulation, particularly the CD38low cells. Taken together, these data suggest that these four subsets represent various stages of a possible differentiation pathway for alpha beta TCR+CD4-CD8- cells, with the HSA+CD38- subset being the most immature while the HSA-CD38low subset is the most functionally mature. These characteristics support the view that alpha beta TCR+CD4-CD8- T cells represent an independent lineage with a distinct, but as yet obscure, role in immunity.

Murine B-cell activation via CD38 and protein tyrosine phosphorylation

CD38 has been implicated in the regulation of both proliferation and rescue from apoptosis of B cells. The signalling events associated with CD38-mediated activation of murine B cells are, as yet, not well defined but it is clear that ligation of CD38 by a mitogenic antibody, NIMR-5, induces a calcium influx in resting B cells. Interestingly, however, cross-linking of CD38 does not mobilize intracellular stores of calcium. We now provide a rationale for these findings by demonstrating that CD38 is not coupled to the generation of inositol phosphates in resting B cells. We do, however, show that CD38 ligation stimulates one, or more, protein tyrosine kinase activities which may play a central role in the transduction of CD38-mediated signals leading to B-cell activation.

Antibodies to murine CD40 protect normal and malignant B cells from induced growth arrest

We have previously described the production of polyclonal anti-murine CD40 antibodies that specifically bind recombinant murine CD40 expressed on L cells and induce vigorous proliferation of normal murine B lymphocytes. The current study utilizes these antibodies to explore the distribution and function of CD40 in murine B cell development. Murine CD40 is expressed at high levels by normal splenic B cells and all Ig-positive B cell lymphomas tested to date. It is not expressed by the 70Z/3 pre-B cell line, BaF3 pre-B cell line, or by numerous T cell and myeloid cell lines. 70Z/3 pre-B cells can be induced to express CD40 by LPS stimulation of the cells. Stimulation of purified splenic B cells with anti-CD40 antibodies causes upregulation of class II MHC antigens, CD23, and ICAM-1 and results in extensive aggregation of the cells. Antibodies to murine CD40 are extremely effective at rescuing malignant and normal B cells from induced growth arrest. Anti-CD40 antibodies protect WEHI-231 and CH31 B lymphoma cells from growth arrest induced by soluble anti-IgM antibodies, TGF beta, or a combination of both stimulants. Similarly, anti-IgM preactivated normal splenic B cells which normally die rapidly from growth arrest after 1 or 2 days culture produce a vigorous proliferative response to subsequent stimulation with anti-CD40 antibodies plus IL-4. Interestingly, anti-CD40 antibodies provide little to no protection against B lymphoma growth arrest induced by immobilized anti-IgM antibodies. These data confirm and extend functional properties assigned previously to human CD40 and identify numerous defined murine model systems to explore the molecular basis of CD40-mediated protection from induced B cell growth arrest.

Antibodies to murine CD40 stimulate normal B lymphocytes but inhibit proliferation of B lymphoma cells

A rat anti-mouse CD40 antiserum has been prepared by hyperimmunisation of Lewis rats with a highly purified preparation of the recombinant extracellular domain of murine CD40. This antiserum specifically binds CD40-expressing L cell transfectants, but not untransfected L cells, and induces vigorous proliferation of highly purified small dense B cells obtained from the spleens of unstimulated mice. Anti-CD40-induced B cell proliferation can be augmented by the addition of IL-4 and is inhibited by purified recombinant soluble mouse CD40. Interestingly the same anti-CD40 antiserum specifically inhibits the in vitro growth of A.20 murine B lymphoma cells. The specificity of this inhibition can be demonstrated by reversing the effect with purified recombinant soluble mouse CD40. These data implicate CD40 as a possible target for therapeutic intervention in the treatment of B lymphomas.

Formation and hydrolysis of cyclic ADP-ribose catalyzed by lymphocyte antigen CD38

CD38 is a 42-kilodalton glycoprotein expressed extensively on B and T lymphocytes. CD38 exhibits a structural homology to Aplysia adenosine diphosphate (ADP)-ribosyl cyclase. This enzyme catalyzes the synthesis of cyclic ADP-ribose (cADPR), a metabolite of nicotinamide adenine dinucleotide (NAD+) with calcium-mobilizing activity. A complementary DNA encoding the extracellular domain of murine CD38 was constructed and expressed, and the resultant recombinant soluble CD38 was purified to homogeneity. Soluble CD38 catalyzed the formation and hydrolysis of cADPR when added to NAD+. Purified cADPR augmented the proliferative response of activated murine B cells, potentially implicating the enzymatic activity of CD38 in lymphocyte function.

Expression cloning of a cDNA encoding a novel murine B cell activation marker. Homology to human CD38

A rat mAb (NIM-R5) has recently been prepared against a novel murine B cell activation marker. We report here isolation of a cDNA (1-19) encoding the B cell-derived protein recognized by NIM-R5 antibody. This cDNA contains an open reading frame that encodes a polypeptide of 304 amino acids with a predicted molecular weight of 34,500. The existence of a 22-amino acid hydrophobic region located 23 amino acids from the amino terminal of the deduced protein, together with four potential N-linked glycosylation sites, characterize the deduced protein encoded by I-19 cDNA as a typical type II transmembrane glycoprotein. Although I-19 cDNA appears to encode a novel murine protein, its nucleotide sequence and deduced amino acid sequence show approximately 70% homology to the previously reported sequence of human CD38, suggesting that I-19 cDNA encodes either the mouse homologue of CD38 or a closely related protein. Northern blot analysis of the expression of this cDNA product in a variety of cell types, together with immunoprecipitation of the recombinant protein expressed in BaF3 cells, indicated that I-19 cDNA encodes not only the epitope recognized by NIM-R5 but also a protein that is indistinguishable biochemically and in terms of distribution from the murine B cell activation marker recognized by NIM-R5 antibody. Chromosomal mapping studies have localized this locus to the proximal region of mouse chromosome 5. We anticipate that the availability of probes for the murine B cell activation marker recognized by NIM-R5, and the recombinant protein itself, will greatly aid efforts to define the role of this molecule in murine B cell development.

Expression cloning of a cDNA encoding a novel murine B cell activation marker. Homology to human CD38

A rat mAb (NIM-R5) has recently been prepared against a novel murine B cell activation marker. We report here isolation of a cDNA (1-19) encoding the B cell-derived protein recognized by NIM-R5 antibody. This cDNA contains an open reading frame that encodes a polypeptide of 304 amino acids with a predicted molecular weight of 34,500. The existence of a 22-amino acid hydrophobic region located 23 amino acids from the amino terminal of the deduced protein, together with four potential N-linked glycosylation sites, characterize the deduced protein encoded by I-19 cDNA as a typical type II transmembrane glycoprotein. Although I-19 cDNA appears to encode a novel murine protein, its nucleotide sequence and deduced amino acid sequence show approximately 70% homology to the previously reported sequence of human CD38, suggesting that I-19 cDNA encodes either the mouse homologue of CD38 or a closely related protein. Northern blot analysis of the expression of this cDNA product in a variety of cell types, together with immunoprecipitation of the recombinant protein expressed in BaF3 cells, indicated that I-19 cDNA encodes not only the epitope recognized by NIM-R5 but also a protein that is indistinguishable biochemically and in terms of distribution from the murine B cell activation marker recognized by NIM-R5 antibody. Chromosomal mapping studies have localized this locus to the proximal region of mouse chromosome 5. We anticipate that the availability of probes for the murine B cell activation marker recognized by NIM-R5, and the recombinant protein itself, will greatly aid efforts to define the role of this molecule in murine B cell development.

A B lymphocyte surface molecule mediating activation and protection from apoptosis via calcium channels

A rat mAb (NIM-R5) was prepared against a 42-kD B cell activation Ag (p42). The expression of p42 is increased upon activation. NIM-R5 induces an increase of intracellular Ca2+, due to influx from the exterior milieu via calcium channels. This stimulation does not prejudice further stimulation with anti-Ig, and thus p42 constitutes an activation signal independent of membrane Ig. The antibody induces increased expression of class II molecules on resting B lymphocytes and prepares the cells for "spreading" when interacted with immobilized anti-class II antibody. The antibody alone is weakly mitogenic and comitogenic with IL-4 on resting B cells. Of particular interest, NIM-R5 induces proliferation and rescue from apoptosis in B cells activated in vitro. In conclusion, NIM-R5 induces an Ig-independent activation and proliferation of resting and activated B cells. This antibody does not recognize other known B cell activation Ag such as CD23, CD40, or CD72. We therefore propose that the p42 Ag is a glycoprotein with an important role in the regulation of B lymphocyte activation and survival.

A B lymphocyte surface molecule mediating activation and protection from apoptosis via calcium channels

A rat mAb (NIM-R5) was prepared against a 42-kD B cell activation Ag (p42). The expression of p42 is increased upon activation. NIM-R5 induces an increase of intracellular Ca2+, due to influx from the exterior milieu via calcium channels. This stimulation does not prejudice further stimulation with anti-Ig, and thus p42 constitutes an activation signal independent of membrane Ig. The antibody induces increased expression of class II molecules on resting B lymphocytes and prepares the cells for "spreading" when interacted with immobilized anti-class II antibody. The antibody alone is weakly mitogenic and comitogenic with IL-4 on resting B cells. Of particular interest, NIM-R5 induces proliferation and rescue from apoptosis in B cells activated in vitro. In conclusion, NIM-R5 induces an Ig-independent activation and proliferation of resting and activated B cells. This antibody does not recognize other known B cell activation Ag such as CD23, CD40, or CD72. We therefore propose that the p42 Ag is a glycoprotein with an important role in the regulation of B lymphocyte activation and survival.

Identification and characterization of the murine homologue of CD22, a B lymphocyte-restricted adhesion molecule

The human B lymphocyte-specific Ag, CD22, is a cell adhesion molecule expressed on the surface during a narrow window of B cell development, coincident with surface IgD. A ligand for CD22 has recently been identified on human T cells as the low molecular mass isoform of the leukocyte common Ag, CD45RO. CD22 has been reported to function in the regulation of both T and B cell activation in vitro. In this study, we report the isolation and expression of a molecular cDNA clone encoding the murine homologue of CD22, mCD22. Within their predicted protein sequences, murine and human sequences overall have 62% identity, which includes 18 of 20 extracellular cysteines and six of six cytoplasmic tyrosines. BHK cells transfected with mCD22 cDNA specifically adhere to resting and activated T lymphocytes and in addition bound activated, but not resting, B cells. Five Th clones were analyzed for their ability to adhere to mCD22; two Th0 clones and one Th1 clone bound CD22+ BHK transfectants, but not all T cell clones bound CD22+ cells: another Th1 clone and a Th2 clone did not. mCD22+ BHK transfectants were also specifically bound by the B cell-specific mAb, NIM-R6, demonstrating that this mAb is specific for murine CD22. Human cell lines expressing the counter-receptors for human CD22 were also examined for adhesion to the murine CD22 homologue; the epitope responsible for B cell adhesion to CD22 is conserved, whereas the T cell epitope binding to CD22 is not. The cDNA and mAb to murine CD22 will be useful for defining the in vivo function of CD22.

Identification and characterization of the murine homologue of CD22, a B lymphocyte-restricted adhesion molecule

The human B lymphocyte-specific Ag, CD22, is a cell adhesion molecule expressed on the surface during a narrow window of B cell development, coincident with surface IgD. A ligand for CD22 has recently been identified on human T cells as the low molecular mass isoform of the leukocyte common Ag, CD45RO. CD22 has been reported to function in the regulation of both T and B cell activation in vitro. In this study, we report the isolation and expression of a molecular cDNA clone encoding the murine homologue of CD22, mCD22. Within their predicted protein sequences, murine and human sequences overall have 62% identity, which includes 18 of 20 extracellular cysteines and six of six cytoplasmic tyrosines. BHK cells transfected with mCD22 cDNA specifically adhere to resting and activated T lymphocytes and in addition bound activated, but not resting, B cells. Five Th clones were analyzed for their ability to adhere to mCD22; two Th0 clones and one Th1 clone bound CD22+ BHK transfectants, but not all T cell clones bound CD22+ cells: another Th1 clone and a Th2 clone did not. mCD22+ BHK transfectants were also specifically bound by the B cell-specific mAb, NIM-R6, demonstrating that this mAb is specific for murine CD22. Human cell lines expressing the counter-receptors for human CD22 were also examined for adhesion to the murine CD22 homologue; the epitope responsible for B cell adhesion to CD22 is conserved, whereas the T cell epitope binding to CD22 is not. The cDNA and mAb to murine CD22 will be useful for defining the in vivo function of CD22.

[Blood concentrations of immunoglobulins in children with vitamin A deficiency]

The object of this study is to measure the influence that vitamin A has upon seric concentrations of different isotypes of immunoglobulins (IgM, IgG, IgA) in children with a normal nutritional state or a slightly subnormal one, as well as that of patients with lower respiratory infections. Fifty two children were studied over a period of 24 months. Twenty eight of these were from an orphanage, while 24 were hospitalized, due to a low respiratory infection. The patients with lower respiratory infection showed normal average concentration of vitamin A, but under that of the orphanage (p less than 0.025). It was also observed that malnutrition influences the seric concentrations of immunoglobulins, which were higher in normal individuals; never the less, when this group show deficiency of vitamin A the serum concentration of IgM became lower in the orphanage, malnutrition children. In a similar way, a lowering of IgG was observed in patients with lower respiratory infections and vitamin A deficiency, while no alterations were found in the serum concentration of IgG in any of the groups studied with vitamin deficiency. It is concluded that the concentrations of vitamin A and the nutritional state modify serum values of IgM and IgG.