Characterization of a carcinogen-induced murine B lymphocyte cell line of C3H/eB origin.

A carcinogen-induced lymphoid tumor, denoted 38C-13, obtained in a T cell-depleted mouse of C3H/eB strain, was adapted to continuous culture in vitro and characterized with respect to its cell surface components. The cells possess IgM class immunoglobulins on their surface but do not secrete it. This membrane IgM is composed of mu and L-chains that are similar in apparent molecular weight to those of an IgM myeloma protein. It is also homogeneous as revealed by isoelectric focusing. The cells possess Fc receptors but lack complement receptors as well as Thy-1 and Ia alloantigens. These characteristics indicate that 38C-13 cells are transformed counterparts of small B lymphocytes at an early stage of differentiation.     

Determination of idiotype-specific T cells in idiotype-vaccinated mice

Immunoglobulin idiotypes (Id) of malignant B lymphocytes and plasma cells are tumor-specific antigens that were extensively used in immunotherapy studies. The effector mechanisms, involved in resistance to tumor following Id vaccination, are a controversial issue. Since cell-mediated responses, rather than antibody responses, constitute powerful effectors against tumors, recent studies focused on the generation of Id-specific T cells. Traditional methods for assessment of cellular responses in murine models of Id vaccination are inadequate because of their low sensitivity and because they do not determine actual frequency of antigen-reactive T cells. Here, we use the highly sensitive enzyme-linked immunospot (ELISPOT) assay for enumeration of interferon gamma (IFN-γ)—secreting cells in Id-vaccinated mice. Our experimental model consists of the murine B-lymphocyte tumor 38C-13, which expresses surface IgM, and the plasma cell tumor D2, which secretes IgM with idiotypic specificity identical to that of 38C-13. Vaccination of mice with purified 38C-13 IgM induced resistance to 38C-13 as well as to D2 tumor cells. Although immunized mice produced high levels of anti-Id antibodies that bound to 38C-13 cells, no binding of antibodies to D2 occurred, suggesting that cellular mechanisms mediated resistance to the plasma cell tumor. ELISPOT assays revealed that immunization induced a significant increase in the frequency of Id-specific IFN-γ-secreting T cells. Depletion of T cell subsets demonstrated that both CD4⁺ and CD8⁺ T cells were involved in the response to Id. This is the first report on application of the ELISPOT assay for enumeration of Id-reactive T cells in a murine model of Id vaccination, providing a tool to study Id-specific T cell responses and to evaluate the efficacy of Id vaccines.     

Immunoglobulin turnover in B lymphocyte subpopulations.

"In vitro" turnover of leucine-labeled and of radioiodinated IgM has been studied with cells from various lymphoid organs of nude mice, i.e. lymph nodes, thoracic duct, spleen and bone marrow, as well as with subpopulations of B cells from spleen and bone marrow separated by free flow electrophoresis. Three types of IgM-producing lymphocytes could be distinguished by their turnover rates of IgM, by the size of the released IgM and by the capacity of the IgM molecules to be labeled by the lactoperoxidase-catalyzed radioiodination reaction and/or by incorporation of radioactive leucine. Type I cells release 7-8 S IgM rapidly (t1/2 = 1-3h); the released IGM is leucine-labeled and radioiodinated. Type II cells release 7-8 S IgM slowly (t1/2 =10-30); the released IgM is leucine labeled and radioiodinated. Type III cells release 19 S IgM rapidly (t1/2 =2-4 h); the released IgM is leucine labeled, but not radioiodinated. Lymph nodes and thoracic duct contain predominantly type II cells, bone marrow contains type I and II cells, spleen contains type I,II and III cells. It is suggested that type III cells are Ig-secreting plaque-forming plasma cells, type II cells are small, resting "memory" B cells, and type I cells may be newly formed antigen-inexperienced B cells.     

A 30-kDa protein is disulfide linked to IgM on normal and neoplastic murine B lymphocytes

Four cloned continuously cultured mouse B lymphoma cells of the lines WEHI-279, BCL1 and 38C-13 were used to study the surface presentation of IgM. Cells of all lines expose, in addition to mu 2L2, various, disulfide-linked subunits as already shown for normal B lymphocytes (Koch, N. and Haustein, D., Mol. Immunol. 1982. 19:477). In contrast to normal B cells, B lymphoma cells also carry IgM structures of higher molecular weight than mu 2L2 on their surface. Furthermore, B lymphoma cells of all investigated lines expose a mu 2L2 structure to which a 30-kDa protein is disulfide-linked. This 30-kDa protein could also be identified on normal mouse B lymphocytes when more drastic conditions were employed. mu 2L2 disulfide linked to this 30-kDa protein is the main IgM structure on normal and neoplastic B cells whereas only small amounts of mu 2L2 (unlinked to this protein) can be detected.     

IgM in bone marrow-derived lymphocytes. Synthesis, surface deposition, turnover and carbohydrate composition in unstimulated mouse B cells

Small B lymphocytes can be depleted by velocity sedimentation on serum albumin gradients of a minor fraction (1 %) of large cells contained in spleen cell populations from normal nu/nu mice. Small cells are the mitogen-sensitive cells. Large cells contain the “background” plaque-forming cells. The populations of large cells synthesize 10 to 100 times more IgM than the populations of small cells. Large and small cells contain IgM as 7–8 S subunits and as smaller precursors of IgM. Carbohydrate moieties of IgM molecules inside small cells contain the “core” sugars glucosamine and mannose attached to the μ-chains, but not the penultimate galactose and the terminal fucose residues common to secreted 19 S IgM. Large cells secrete IgM as 19 S pentamers, small cells shed their IgM as 7–8 S subunits. Large cells turn over IgM with a half time around 4 h, small cells turn over IgM with a half time between 20 and 80 h IgM synthesis is actinomycin D-resistant in large cells and actinomycin-sensitive in small cells. Surface-bound IgM molecules can be distinguished within the total cellular pool from IgM molecules situated in intracellular compartments not exposed to the outside by their serological reaction with polyvalent anti-Ig antibodies on intact cells. With this reaction it can be show that small cells contain over 90 % of their IgM in the surface membrane.     

Immunoglobulin turnover in B lymphocyte subpopulations

“In vitro” turnover of turnover of leucine-labeled and of radioiodinated IgM has been studied with cells from various lymphoid organs of nude mice, i.e. lymph nodes, thoracic duct, spleen and bone marrow, as well as with subpopulations of B cells fromspleen and bone marrow separated by free flow electrophoresis. Three types of IgM-producing lymphocytes could be distinguished by their turnover rates of IgM, by the size of the released IgM and by the capacity of the IgM molecules to be labeled by the lactoperoxidase-catalyzed radioiodination reaction and/or by incorporation of radioactive leucine. Type I cells release 7—8 S IgM rapidly (t_1/2 = 1—3 h); the released IgM is leucine-labeled and radioiodinated. Type II cells release 7—8S IgM slowly (t_1/2 = 10—30); the released IgM is leucine labeled and radioiodinated. Type III cells release 19 S IgM rapidly (t_1/2 = 2—4 h);the released IgM is leucine labeled, but not radioiodinated. Lymph nodesand thoracic duct contain predominantly type II cells, bone marrow contains type I and II cells, spleen contains type I, II and III cells. It is suggested that type III cells areIg-secreting, plaque-forming plasma cells, type II cells are small, resting “memory” B cells, and type I cells may be newly formed antigen-inexperienced B cells.     

Characterization of B cells in severe combined immunodeficiency disease

The circulating lymphoid cells of eight consecutive untreated infants with severe combined immunodeficiency disease (SCID) with B cells were analyzed for surface marker expression and function. The B cells of these children expressed sIg, HLA-DR, CD19 (B4), CD20 (B1), CD21 (B2), Leu-8, and lacked expression of CD10 (CALLA), as do normal peripheral blood B lymphocytes. SCID B cells also expressed antigens that are normally absent or present on only a minor subset of circulating adult B lymphocytes, including CD1c (M241), CD38 (OKT10), CD23 (PL13), with or without concomitant CD5 (Leu-1) expression. The B cells of these children were capable of proliferating in vitro when stimulated with Staphylococcus aureus Cowan I. However, in the presence of pokeweed mitogen, S. aureus Cowan I, and normal T cells, the sIg+ cells of these children produced only IgM. Studies performed on normal B cells obtained from cord blood, young children, and adults reveal that whereas cord blood B cells are predominantly CD1c, CD38, and CD23 positive, B-cell expression of these antigens decreases with age. Cord blood B cells, similar to SCID B cells, produce only IgM when stimulated in vitro with pokeweed mitogen and S. aureus Cowan I. Based on these observations, we hypothesize that SCID B cells represent a population of B cells present during normal B-cell ontogeny which becomes a minor subset when an individual develops full immunologic competence.     

A B7-1-transfected human melanoma line stimulates proliferation and cytotoxicity of autologous and allogeneic lymphocytes

B7 co-stimulation is necessary to activate resting T cells upon antigen recognition by the T cell receptor. To see whether expression of B7 may render human melanoma cells able to stimulate T cells, a cloned melanoma line (Me1B6), which did not express B7-1, was transfected with the human B7-1 gene. In proliferation assays, B7-1 transfected cells (Me1B6/B7) showed greater stimulatory activity of allogeneic and autologous peripheral blood lymphocytes (PBL) compared to parental, non-transfected tumor cells. This effect was also seen when allogeneic CD8⁺ and CD4⁺ subpopulations were used as effectors. In these studies, activation of lymphocytes was B7-1-dependent and HLA classes I and II mediated. The higher proliferation correlated with an increased lytic activity by PBL stimulated with B7-1⁺ tumor cells against the untransfected Me1B6. Furthermore, PBL from a metastatic melanoma patient stimulated by Me1B6/B7 developed an higher lytic activity not only against Me1B6 but also against their autologous, B7-1^? tumor. Finally, after Me1B6/B7 stimulation, PBL released interleukin (IL)-2 and interferon-γ, but not IL-4, suggesting a Th1-mediated response. These data support the use of B7-1 transfected melanoma cells in the therapeutic vaccination of melanoma patients.     

Ontogeny, distribution and function of CD38-expressing B lymphocytes in mice

Analysis of expression of CD38, CD45R (B220), IgM and IgD on splenic B lymphocytes from mice of different ages demonstrated CD38 on both immature (B220(+), BCR(-)) and mature (B220(+), BCR(+)) B lymphocytes. Similarly, CD38 is expressed as early as B220 on the surface of progenitor B cells in the bone marrow. In spite of expressing of CD38 and IgM, neonatal B cells, in contrast to the adult, failed to proliferate to either anti-CD38 or anti-IgM cross-linking when IL-4 was present. They did, however, respond to LPS and anti-CD40, and by 2 weeks of age they began to respond to anti-CD38 and anti-IgM, reaching adult B cell levels by 4 weeks. Although the distribution of CD38 on adult B cells from most different lymphoid compartments was broadly similar, significantly higher levels of CD38 were expressed on peritoneal B lymphocytes. A detailed analysis, using IgM / IgD ratio and staining with anti-CD5 confirmed that B1 lymphocytes were expressing a high level of CD38. Interestingly, both immature B cells and peritoneal B1 lymphocytes were unresponsive to anti-CD38. However, they were activated by LPS or anti-CD40.     

Turnover of radioiodinated and of leucine-labeled immunoglobulin M in murine splenic lymphocytes

Lactoperoxidase-catalyzed radioiodination of cell surface proteins and biosynthetic incorporation of tritiated leucine were used to study the size and turnover of cell-associated immunoglobulins in splenic lymphocytes of different size from BALB/c, C3H, and nu/nu mice. Small spleen cells, separated from large cells by velocity sedimentation, showed a single slow rate of turnover (t_1/2= 10–30 h) of surface radioiodinated or leucine-labeled IgM released as the monomeric 7–8 S subunit of IgM. Mitogen-activated large B cells and nonstimulated large spleen cells, separated by velocity sedimentation, released leucine-labeled IgM in an initial rapid phase (t_1/2= 2–4 h) as 19 S IgM, and later released 7–8 S IgM slowly (t_1/2= 10–30 h). The iodination reaction changed neither the biphasic mode of turnover, nor, even at higher concentration of H₂O₂, the size of the actively secreted 19 S IgM. Radioiodination of mitogen-activated large cells or of unstimulated large cells labeled only the slowly released 7–8 S IgM, not the actively secreted 19 S IgM. Large cells of nonstimulated spleen, however, released radioiodinated as well as leucine-labeled IgM also rapidly (t_1/2= 1–3 h). These rapidly released IgM molecules were found to be 7–8 S IgM subunits. Our results indicate that these turnover rate and size differences of radioiodinated and of leucine-labeled IgM released from murine spleen cells are in part resulting from the differences in the methodology of labeling and are in other parts due to different small and large splenic lymphocytes releasing IgM of different size at different rates.     

Detection of unique peptides derived from the mu chains of cell surface but not secreted IgM

IgM is present on the surface of B lymphocytes in monomeric form and can also be secreted into the serum in pentameric form after differentiation of B cells into plasma cells.We have previously used a monoclonal population of murine tumor cells (BCL₁) which express surface IgM but can also secrete IgM after stimulation with lipopolysaccharide to study the primary structure of μ chains from cell surface and secreted IgM. Using cation exchange chromatography, we detected a peptide present only in μ chains from secreted IgM but not in cell surface IgM. The putative extra peptide(s) from the cell surface μ chain could not be identified perhaps due to its inability to bind to the exchange resin. In the present study we have used reverse phase high pressure liquid chromatography to analyse the peptides of μ chains from cell surface and secreted IgM from both BCL₁ tumor cells and from normal B lymphocytes. Our results demonstrate the presence of two peptides associated with the Fc portion of the cell surface but not with the secreted μ chain.     

Age dependency and mutual relations in T and B lymphocyte abnormalities in common variable immunodeficiency patients

Common variable immunodeficiency (CVID) is primary hypogammaglobulinaemia with an unknown aetiopathogenesis. Although various abnormalities of T and B cells have been described, their pathogenetic roles are unclear. We determined T and B lymphocyte subsets known to be abnormal in CVID in order to disclose possible relations between numerical abnormalities in those cells. Markers associated with B cell development (CD21, CD27, IgM, IgD) were determined on B lymphocytes (CD19+); T lymphocyte development (CD45RA, CD45RO, CD62L) and activation markers (CD25, CD27, CD28, CD29, CD38, CD57, HLA-DR) were determined on CD4+ and CD8+ T lymphocytes in 42 CVID patients and in 33 healthy controls. Abnormalities in CD4+ T lymphocyte activation markers (increase in CD29, HLA-DR, CD45RO, decrease in CD27, CD62L, CD45RA) were observed particularly in patients with a decreased number of memory (CD27+) and mature (CD21+) B cells (group Ia according to the Freiburg group's classification), while abnormalities observed in CD8+ cells (increase in CD27 and CD28 and decrease in HLA-DR, CD57 and CD38) did not depend upon grouping patients together according to B lymphocyte developmental subpopulations. We observed correlations between immature B cells (IgM+ CD21-) and expression of CD27, CD62L, CD45RA, CD45RO and HLA-DR on CD4+ T cells in CVID patients but not in the control group. The expression of CD27 and CD45RA on CD4+ T lymphocytes, such as the percentage of IgD+ CD27- and IgD+ CD27+ cells in B lymphocytes, showed age dependency to be more significant than in the control group. Our study demonstrates that T and B lymphocyte abnormalities in CVID are partially related to each other. Some of those abnormalities are not definite, but may evolve with age of the patient.     

Signaling through murine CD38 is impaired in antigen receptor-unresponsive B cells

CD38 is a 42-kDa membrane associated enzyme which converts NAD into cyclic ADP-ribose (cADPR), a Ca²⁺-mobilizing second messenger, and ADP-ribose (ADPR). Agonistic antibodies to murine CD38 deliver a potent growth co-stimulus to mature splenic B lymphocytes. In this report we demonstrate a striking relationship between CD38-mediated mitogenesis and the ability of surface IgM to promote B cell proliferation. Tolerized B lymphocytes obtained from a double-transgenic mouse model of B cell tolerance do not proliferate in response to antigen stimulation through the Ig receptor or to agonistic anti-CD38 antibodies. Similarly, B-1 cells isolated from the peritoneal cavity of normal mice, and splenic B cells isolated from newborn mice were also unresponsive to both anti-IgM and anti-CD38 stimulation. All of these CD38-unresponsive B cells expressed normal levels of cell surface CD38 and responded to numerous other stimuli. CD38 immunoprecipitated from these B cell populations was normal in size and effectively hydrolyzed NAD, suggesting that the defect in CD38 signaling likely occurs downstream of CD38 itself. Signaling through CD38 and IgM does not always have identical effects on B cells since anti-CD38 cannot deliver inhibitory growth or differentiation signals to normal B cells or immature B cell lines. Nevertheless, the correlative data with these multiple B cell models of unresponsiveness suggests that the signaling pathway utilized by CD38 and IgM intersect, possibly sharing at least one of the crucial components of the Ig receptor signaling cascade.     

Epstein-Barr virus (EBV) receptor implantation onto human B lymphocytes changes immunoglobulin secretion patterns induced by EBV infection

Mosaic membrane vesicles containing both Epstein-Barr virus (EBV) receptors and Sendai virus envelope proteins were allowed to form by the previously described membrane solubilization and co-reconstitution technique. The vesicles were allowed to fuse with the membranes of normal human B lymphocytes, whereafter the cells were infected with transforming EBV (B95-8 substrain). Compared to similarly infected but otherwise unmanipulated cells, the receptor-implanted lymphocytes responded with a larger number of EBV-determined nuclear antigen positive and immunoglobulin-secreting plaque-forming cells (PFC). Moreover, there was a clear increase of the IgG/IgM PFC ratio in the receptor-implanted B lymphocytes. These results show that not all human B lymphocytes that can potentially be activated by EBV express functional EBV receptors. B lymphocytes programmed to secrete IgG appear to be more defective in this respect than IgM secretors.     

In vivo and in vitro IgE isotype switching in human B lymphocytes: Evidence for a predominantly direct IgM to IgE class switch program

Molecular analysis of circular excision products and composite genomic switch regions has demonstrated that in mice, immunoglobulin (Ig) isotype switching from IgM to IgE often proceeds sequentially via IgG1. Based on analysis of Ig production in cell cultures, it has been suggested that human B cells may switch to IgE via IgG4, whereas limited molecular data from in vitro switched B cells suggest a direct IgM to IgE switch program. To obtain a quantitative assessment of direct versus sequential IgE switching in humans, we have analyzed the nucleotide sequences of 29 composite Sμ/S? switch regions from freshly isolated human B lymphocytes from patients with atopic dermatitis and from B lymphocytes induced to switch to IgE synthesis in vitro. The data show that in these B cells IgE isotype switching progressed directly from IgM to IgE. We conclude that, in contrast to the murine IgM/IgE switch program, the IgM to IgE switch in B lymphocytes from patients with atopic dermatitis as well as in vitro stimulated B cells from healthy donors preferentially proceeds via direct Sμ to S? switch recombination.     

GL7 defines the cycling stage of pre-B cells in murine bone marrow.

We have identified a novel subset of early B lineage cells in the mouse bone marrow (BM) by GL7 expression on cell surface. GL7(+)B220(low) BM cells have a large cell size and are CD43(-to low), CD95(-), Sca-1(-), I-A(low), IgM(-) and IgD(-), suggesting that they are large pre-B cells. These BM cells express lambda5 and VpreB but not terminal deoxytransferase (TdT) and Bcl-2, and approximately 50 % of them are in cell cycle. This fraction was not detected in BM cells of Rag-1-deficient and Scid mice, supporting that GL7(+)B220(low) BM cells belong to fraction C' and D according to Hardy's criteria or to an early large pre-B-II fraction according to Melchers-Rolink's criteria. Furthermore, GL7(+)B220(low) BM cells can differentiate into IgM(+) immature B cells in co-culture with stromal cells. These results suggest that B lymphocytes pass through the GL7(+) pre-B cell stage during differentiation in the BM. Thus, GL7 is the critical marker to define the proliferation stage of large pre-B cells.     

Double labeling immunohistologic and flow cytometric analysis of human B cells with particular reference to Leu-8 expression

Previous results have shown that human lymphocyte subpopulations are heterogeneous as to Leu-8 expression. In the present study, we performed a heretofore unreported immunohistologic analysis and flow cytometric double labeling investigation focused on Leu-8+ and Leu-8- human B cells, with special reference to their expression of other B cell lineage antigens (Leu-14, B1, OKB7 or B2, OKB2, BA-1, BA-2, IgD, and IgM) or of a functional marker of cell proliferation (Ki-67). Immunohistologic analysis was performed on frozen sections of nine normal or reactive lymph node and tonsil biopsy specimens tested with either single or paired antibodies, the latter procedure (double labeling) being directed at revealing positively subtracted Leu-8+ or Leu-8- cells expressing a given marker depending on the antibody staining sequence used. Dual flow cytometry with paired antibodies was performed on cell suspensions from four normal or reactive lymph nodes and tonsils. As to the follicular district, immunohistologic analysis suggests that germinal center (proliferating) B lymphocytes, identifiable in cell suspension as Leu-8-B1+ and representing 80% of the B1+ cells, are Leu-8- and Leu-14+, BA-2+, OKB7+, and IgM+, being rarely IgD+. Most lymphocytes located in the mantle zone (resting cells), identifiable in cell suspension as Leu-8+B1+ and representing the remaining 20% of the B1+ cells, are Leu-8+, Leu-14+. OKB7+, OKB2+, BA-1+, IgD+, and IgM+. Furthermore, from our results, there is indirect evidence to support the existence of a Leu-8+BA-2+ lymphocyte subset located in the mantle zone. Immunohistologic study of four lymph nodes by Leu-8 and Ki-67 antibody (that recognizes a nuclear, cell proliferation-associated antigen absent only in the Go phase of the cell cycle) showed that these markers are mutually exclusive and added further evidence that Leu-8 antigen is a marker of resting lymphocytes.     

Receptors for IgM on Human B Lymphocytes

Using a rosette technique with IgM coated bovine red blood cells (EA-IgM) receptors for IgM can be demonstrated on human B-lymphocytes. While in the peripheral blood B cells with IgM receptors are found only occasionally, between 7 and 33%, mean 16%, of tonsil B-lymphocytes exhibit receptors for IgM. This was shown in double marker studies using EA-IgM for the demonstration of IgM receptors and fluorochrome labelled conjugates for the demonstration of S-IgD, S-IgM and B cell antigens. These receptors are specific for IgM, they can be completely blocked by IgM-anti OVA complexes and partially by free IgM, but not at all by aggregated human IgG. They are sensitive to trypsin and pronase but reconstitute after further incubation at 37 degrees C. These data show that not only T and CLL cells but also some normal B-lymphocytes have receptors for IgM. We favour the view that CLL lymphocytes may derive from these B-lymphocytes, which may represent a certain maturation step in B cell development.     

Effect of copper-dextran complex (C-79) on the immunity indices in normothermic rabbits and in postpyrogenic fever

The complex combination of bivalent copper with 3-mercapto-2-hydroxypropyl ether of dextran (preparation C-79) was intravenously injected to normothermic rabbits in the doses 0.04 mg/kg, 0.4 mg/kg and 0.8 mg/kg and additionally in the dose of 0.4 mg/kg to febrile rabbits with fever induced by i.v. administration of 0.32 micrograms/kg LPS from E. coli. The following indices were determined: killing and phagocytic capability of peripheral blood neutrophils, migration of lymphocytes, number of T and B cells and number of cells producing IgM after SRBC immunization. Normothermic rabbits responded to C-79 administration by: increase of killing capability of peripheral blood neutrophils, enhanced formation of rosettes against RRBC and EAC rosettes, increased amount of IgM producing cells and inhibition of migration activity of peripheral blood lymphocytes. As a result of the interaction with bacterial pyrogen, C-79 potentiates and prolongs the stimulatory effect of LPS on the killing ability and phagocytic activity of neutrophils, prolongs the mitogenic effect of LPS on B lymphocytes and potentiates the immunogenic effect evidenced by the increased number of IgM producing cells.