Partial characterization of different cell types found in the Xenopus laevis lymphoreticular tumor based on the presence or absence of surface immunoglobulins and Fc molecules

Cells of Xenopus laevis lymphoreticular tumor induced by tumor tissue transplantation were examined for surface Ig and Fc receptor molecules in order to evaluate the different cell types found in the tumor. Direct immunofluorescent technique, using fluorochrome conjugated rabbit antisera to Xenopus Ig's, detected Ig molecules on the surface of a mean of 31.7 +/- 11.3% of cells in tumor suspensions. Most of these molecules were of IgM isotype, reversibly bound to the cell membrane (cytophilic) and could be dissociated by acid pH or overnight cell culturing. In addition integral membrane IgM was detected on the surface of 10.2 +/- 5.9% of the cells. The serum origin of cytophilic Ig's and the cellular origin of integral membrane Ig's were confirmed by analysis of electrophoretic mobility of their heavy chains on SDS-polyacrylamide gels. The existence of Fc receptor molecules on the surface of 48.6 +/- 16.6% of the cells was demonstrated by fluorescent staining using heat aggregated FITC labelled IgM or FITC or TRITC labelled antigen-complexed IgY antibodies. 32.2 +/- 12.4% and 16.4 +/- 6.8% of the cells bore receptors for IgY or receptors for IgM respectively, while 6.3 +/- 3.1% carried receptors for both Ig's. Double fluorescent staining revealed that 28.9 +/- 4.5% of cells bearing IgM on their surface expressed also receptors for IgY. These results attest to the heterogeneity of the tumor cell population, in respect to the presence or absence of FcR-IgY, FcR-IgM, sIgM, and cytophilic IgM surface molecules.     

IgD expression on B cells is more efficient than IgM but both receptors are functionally equivalent in up-regulation CD80/CD86 co-stimulatory molecules

The expression and function of IgM and IgD antigen receptors were studied in a series of anti-hen egg lysozyme (HEL) immunoglobulin (Ig)-transgenic mice expressing either IgM alone, IgD alone, or both IgM and IgD. B cell surface expression of IgD was found to be more efficient than that of IgM. Thus antigen receptor density on IgD⁺, IgM^? B cells was twofold higher than on IgM⁺, IgD^? B cells despite the presence of sevenfold lower levels of membrane heavy chain mRNA, and coexpression of IgD with IgM led to almost complete inhibition of surface IgM. In addition, less extensive down-regulation of IgD occurred following exposure to antigen in vitro. When regulation of CD80/CD86 co-stimulatory molecules by surface Ig was examined, up-regulation of the former was initiated at lower antigen concentrations on IgM^?, IgD⁺ compared to IgM⁺, IgD^? B cells. On correcting for antigen receptor density, however, induction of CD80/CD86 by IgM and IgD was comparable. Taken together, these results reinforced the functional similarity of IgM and IgD antigen receptors while at the same time revealing differences in expression which may explain their simultaneous presence on mature B cells.     

Membrane immunoglobulins of spontaneous B lymphomas of aged BALB/c mice

Four cell lines derived from spontaneous BALB/c lymphoma tumors were analyzed with regard to the type of their membrane immunoglobulins (Ig). Using lactoperoxidase iodination of membrane proteins combined with immunoprecipitation and electrophoresis on polyacrylamide gel, three of these cell lines (X16c, L10A and K46) were found to express the monomeric form of IgM and IgD as well as half molecules. One cell line (M12) lacked both IgM and IgD. The apparent mol. wt of the lymphoma micro chain was about 80 000 and exceeded the mol. wt. of 75 000 determined for micro chains secreted by myeloma cells. The mol. wt. of the delta heavy chain was found to be 66 000. Immunofluorescence showed that the L10A and X16c lines expressed lambda light chains on their cell surface. Another Ig-bearing cell line (K46) expressed both lambda and kappa chains. Thus, three out of the four B lymphomas examined expressed both IgM and IgD with light chains of the Lambda type. These results, together with our previous findings which demonstrate the presence of Ia and Fc receptors on the same cells, indicate that spontaneous B lymphomas in BALB/c mice are the malignant counterpart of mature B lymphocytes.     

A study of the immunoglobulin classes present on the membrane and in the cytoplasm of human tonsil plasma cells

The problem of whether immunoglobulin (Ig)-containing plasma cells expressed membrane Ig has been investigated using cells from human tonsils. In tonsils, IgG-containing cells are predominant, but a certain number of IgM, IgA and IgD-containing cells are also present. By using a double staining immunofluorescent technique for the simultaneous detection of membrane and intracytoplasmic Ig, it has been possible to ascertain that the large majority of IgA, IgM and IgD-containing cells had membrane immunoglobulin (mIg) of a class coincident with that of intracytoplasmic Ig. In addition a noticeable proportion of IgM-containing cells expressed membrane IgD, thus indicating that a certain number of these cells bore both membrane IgM and IgD. About 60 % of IgG-containing cells had membrane IgG, while the remaining cells did not express mIg. Furthermore the surface staining of these cells was generally fainter than that of the cells containing other Ig classes. Experiments on the surface light chain type expressed by the single Ig-containing cells (IgCC) as compared to that found in the cytoplasm have shown that in the large majority of IgCC the light chain type of mIg coincided with that of intracytoplasmic Ig. Discordant light chain types of membrane and cytoplasmic Ig were found on about 12% of IgCC only. These values can be taken as a measure of how many IgCC had passively acquired mIg.     

Membrane Ig on human lymphocytes: rate of turnover of IgD and IgM on the surface of human tonsil cells

The turnover of IgM and IgD molecules present on the membrane of human tonsil cells has been studied using immunofluorescence and peroxidase-catalyzed membrane radioiodination. With the first of the two techniques cells were treated with pronase to remove membrane immunoglobulin (mIg), placed in culture and stained at intervals to check the reappearance of membrane IgD and IgM on the cell membrane. These experiments showed that membrane IgD (in contrast to membrane IgM) are extremely susceptible to proteolysis. Furthermore, cells treated with a concentration of pronase found to be optimal to remove membrane IgM failed to re-express membrane IgD in vitro. The large majority of tonsil lymphocytes has both membrane IgM and IgD. Due to the different behavior of re-appearance of the two membrane molecules after treatment with pronase, it was not possible to obtain the simultaneous re-expression of membrane IgM and IgD by the cells “stripped” with pronase. However, the two molecules were re-ex-pressed in vitro by the cells treated with different pronase concentrations with a similar timing, i.e. 50 % or more of the cells re-expressed membrane IgD and IgM after 8 h in culture. ¹³¹I-radioiodinated membrane IgD and IgM were also released from the cell surface with a. similar timing, the half-life of permanence on the cell membrane being about 4 h for both molecules. These findings thus indicate that IgM and IgD molecules have a similar turnover and that a cell is capable of placing two different Ig molecules at a time on its surface.     

白血病细胞系和扁桃体细胞膜流动性测析及单抗对其调控研究

本文采用疏水性荧光探针DPB(1,6-dipheny1-1,3,5-hexatriene,1,6-二苯-1,3,5-己三烯)检测B淋巴细胞白血病细胞系及正常扁桃体细胞膜的流动性。同时采用间接免疫荧光试验测定了上述细胞与抗白血病蛋白IgM单抗的反应性。实验结果表明,恶性细胞膜流动性明显大于正常扁桃体细胞,抗白血病同种型单抗SM_(11)与白血病细胞系,及扁桃体细胞呈阳性反应,并对其细胞膜的流动性有不同程度的增强作用。而抗独特型单抗仅与白血病细胞系起反应和对其细胞膜流动性有增强作用,对扁桃体细胞膜流动性无影响。提示单抗对相应细胞膜流动性有增强作用。     

Cell surface immunoglobulin. VI. Dynamics on a human lymphoma line

Release of cell surface Ig and secretion of Ig has been studied in Daudi cells, a human lymphoma cell line synthesizing IgM that appears to be a neoplastic counterpart of B lymphocytes. In contrast to murine splenocytes, virtually no internally labeled Ig and only a small proportion of cell surface Ig are released during 8 hours of in vitro incubation. Released cell surface Ig can be recovered in the medium predominantly as 8 S IgM monomer probably attached noncovalently to a fragment of plasma membrane. This shedding of cell surface Ig appears to be dependent on the prior culture phase of the cells. Thus, in cells from cultures kept at high density, there was greater release of cell surface Ig apparently associated with cell death.     

Detection by indirect immunofluorescence of Fc receptors in cells acutely infected with Herpes simplex virus.

In attempting to use the indirect fluorescent antibody test (IFA) to measure antibodies to herpes simplex virus (HSV), we found that all human sera gave a positive reaction with Chang liver cells infected with type 1 (HSV). All sera gave equivalent titers of 320-640 for acetone-fixed cells and about 40 for live cells (membrane fluorescence) in the presence of fluorescein-labeled antisera to human Ig; none of the sera reacted with uninfected cells. The fluorescence seen in fixed cells was primarily cytoplasmic; some cells showed a diffuse fluorescence, obscuring the demarcation between the nucleus and cytoplasm. Purified IgG from antibody-negative human sera and a purified Fc fragment of IgG were positive both for cytoplasmic and membrane fluorescence, whereas F(ab')2, IgM and IgA were unreactive. The reaction was also seen when an antiserum conjugate specific for the Fc fragment of IgG was used. The reactive IgG was present in freshly prepared plasma and serum; it could not be removed from serum either by ultracentrifugation or by serial absorption with HSV-infected cells. These findings suggest that the nonspecificity of the IFA results from the formation of low-avidity bonds between the large mass of native serum IgG and an Fc receptor on the plasma membrane and in the cytoplasm of cells infected with HSV. The results also suggest that extreme caution be exercised in attempting to use the IFA in the serodiagnosis of infections with HSV and perhaps the other human herpes-viruses.     

Immunoglobulin receptors on human leucocytes. III. Comparative study of human bone marrow and blood B cells: role of IgM receptors

A comparative study of B cells present in human bone marrow and blood was performed. In both compartments the cells carrying the Ig receptors were found to be small mononuclear cells. Predominance of IgM receptors was found on bone marrow cells whereas Ig receptors present on peripheral blood cells were predominantly of the IgG class. Bone marrow lymphoid cells of non-sensitized donors were capable of binding a primary antigen, keyhole limpet haemocyanin (KLH) and could be retained on glass bead columns coated with either KLH or with goat anti-human IgM antiserum but not with anti-IgG. Whereas bone marrow cells of donors immunized with KLH 16–27 days earlier lacked KLH reactive cells, the latter cells could be demonstrated in the blood. It is concluded that human bone marrow B cells carrying IgM receptors are essential for the early antigen recognition step following which recruitment of these cells into the circulation takes place.     

B cells are anergic in transgenic mice that express IgM anti-DNA antibodies

B lymphocytes in individuals with systemic lupus erythematosus (SLE) secrete pathogenic auto antibodies to DNA which cause clinical nephritis. (NZB x NZW) Fl (BW) female mice also secrete pathogenic anti-DNA auto antibodies, and therefore are considered to be an animal model of SLE. The rearranged immunoglobulin (Ig) genes that encode an anti-DNA antibody from a diseased BW mouse have been cloned, and transgenic (Tg) mice have been created by microinjection of these constructs into fertilized eggs from normal mice. As we reported previously, when the construct contains the Cγ2a heavy chain constant (C_H) region, the mice spontaneously secrete anti-DNA IgG and they develop mild nephritis. This demonstrated that the Ig encoded by the transgene is pathogenic. In contrast, here we report that when the construct contains the same anti-DNA Ig variable (V) regions used previously, along with the Cμ region, the auto reactive B cells are rendered tolerant. Most B cells in the Tg mice express the μ transgene product on their surface, and rearrangement of endogenous light chain genes is partially suppressed. Furthermore, most hybridomas made from Tg B cells secrete IgM anti-DNA. Despite this, the Tg mice have reduced levels of total serum Ig and they do not secrete anti-DNA IgM either spontaneously or following immunization with DNA. We conclude that most B cells in the Tg mice have been rendered anergic. Anergy is however reversible in vitro; lipopolysaccharide stimulation of Tg B cells leads to the production of a significant amount of IgM anti-DNA antibody. The studies demonstrate that in this line of Tg mice on a normal mouse genetic background potentially pathogenic B cells that express a high-affinity Ig specific for a natural autoantigen are subject to tolerance by induction of anergy.     

Anti-B cell autoantibodies encoded by VH 4–21 genes in human fetal spleen do not require in vivo somatic selection

We isolated immunoglobulin (Ig) V_H4 genes that were rearranged in the genomic DNA of 160 day human fetal spleen. Productively rearranged V_H 4-21 genes were cloned into pRTM1, a human IgM expression vector. This allowed us to generate IgM?K-expressing transfectomas by co-transfecting each of these constructs with pSVG-V?K3, an Ig ?K light-chain expression vector that has a variable region encoded Humkv325, a conserved V?K gene that is frequently expressed early B cell ontogeny. We find that all transfectomas expressing IgM?K encoded by V_H 4-21 make IgM autoantibodies reactive with i, a linear poly-N-acetyllactosamine determinant present on neonatal red blood cells and a B cell-restricted isoform of the CD45 surface molecule. In contrast, a transfectoma expressing pSVG-V?K3 and pRTM1 containing a rearranged V_H4-59 (V71-4) gene isolated from a chronic lymphocytic leukemia B cell population, designated WIL, produced IgM?K antibodies that had no detectable anti-i binding activity. However, transfectomas expressing V_H 4-21 fused onto the Ig heavy-chain third complementarity determining region (CDR3) of WIL are found to make anti-B cell autoantibodies with anti-i activity. These studies indicate that V_H 4-21 genes rearranged in human fetal B cell ontogeny can encode anti-B cell autoantibodies with a binding specificity that does not require in vivo somatic selection.     

Mucosal and glandular distribution of immunoglobulin components: Immunohistochemistry with a cold ethanol-fixation technique

Precise immunohistochemical information about the mucosal distribution of diffusible immunoglobulin (Ig) components and the local occurrence of Ig-containing cells can be obtained by studying in parallel directly fixed and saline-extracted biopsy specimens. This combined approach is useful for evaluating systemic and local contributions to the mucosal Ig supply in patients with immunodeficiency. Their mucosal populations of Ig-bearing cells can also be demonstrated immunohistochemically.

A new model for the secretory Ig system is based on experience with this technique applied to normal mucosal specimens from various levels of the human respiratory and gastrointestinal tract. The serous-type secretory epithelial cell produces secretory component (SC) and is also responsible for the selective external transfer and molecular completion of secretory IgA and secretory IgM. Cell surface-associated SC most likely mediates the epithelial affinity for dimeric IgA and 19S IgM, and Ig—SC complexes are probably formed and mobilized in the cell membrane; they may then reach the cytoplasm outside the Golgi apparatus by pinocytosis or facilitated diffusion. The composite molecules finally appear to be extruded into the gland lumen along a general secretory pathway.

     

The role of surface ig binding in the activation of human B cells by phosphorothioate oligodeoxynucleotides

Phosphorothioate oligodeoxynucleotides (sODNs) can induce T-cell-independent polyclonal activation of human B cells by a mechanism that depends on both sequence and back-bone structure. Because matrix-bound as well as soluble sODNs are mitogenic, this stimulation may result from the engagement of surface receptor(s). In order to investigate whether surface immunoglobin (Ig) could be a receptor for sODNs, the interaction of sODNs-fluorescein isothiocyanate (FITC) with Ig-coated beads was examined. sODNs specifically bound to human IgM and IgG. Moreover, binding of sODN to human B cells induced temperature-dependent capping of bound receptors and colocalization of FITC-sODN and IgM into aggregated caps on the surface of human B cells. A role of surface Ig was furthermore shown by observations that antibody-mediated capping of B-cell surface IgM or IgD inhibited subsequent binding of sODNs and that the capacity of sODN to stimulate human B cells was blocked by excess IgM or IgG, by nonstimulatory antibodies to sIgM, as well as by a variety of negatively charged molecules. Together, these results indicate that sODNs engage surface Ig by charge-charge interactions that lead to activation of human B cells.     

In vitro immunoglobulin production by mononuclear cells in rheumatoid arthritis

Since patients with rheumatoid arthritis (RA) exhibit serum hypergammaglobulinemia and autoantibody (rheumatoid factor) production, we compared elaboration and control of in vitro RA mononuclear cell (MNC), Ig assayed by enzyme-linked immunoassays or by hemolytic plaque formation, in 37 RA patients and 17 normal subjects. We found (1) RA spontaneous plaque-forming cells were significantly reduced (RA 344 vs normal 627 PFC/10(6) MNC, P less than 0.002); (2) RA spontaneous IgG and IgM (but not IgA) elaboration was significantly diminished (IgG RA 339, normal 776; IgM RA 255, normal 869 ng/ml, P less than 0.001; IgA RA 87, normal 124); (3) RA stimulated IgG and IgM production (but not IgA) was also decreased (IgG RA 2434, normal 3862, P less than 0.06; IgM RA, 1676, normal 3323, P less than 0.005; IgA RA 1859, normal 2315); (4) reduced RA Ig elaboration was not clearly due to altered numbers of T or non-T cells, age, medications, clinical features of disease, or response kinetics; (5) relative improvement of RA in vitro IgG, but not usually IgM, secretion followed removal of adherent cells, addition of indomethacin or addition of mitomycin C-treated T cells; (6) MNC from synovial fluids, but not bone marrows, exhibited spontaneous Ig production in excess of stimulated synovial fluid cellular or peripheral blood Ig elaboration. These observations indicate selective impairment of peripheral blood MNC IgG and, particularly, IgM secretion in RA. This defect appears to reflect accessory cell influences which differ from normal as well as the sequestration of primed or activated cells in the synovial fluid.     

Phylogenetic origins of immune recognition: lymphocyte surface immunoglobulins and antigen binding in the genus Carassius (Teleostii).

Virtually all lymphocytes (from thymus, spleen and head nephros) of two closely related cyprinoid fish, C. auratus and C. carassius, were shown to bear surface immunoglobulin (Ig) detectable by immunofluorescence. Nonlymphoid cells (for example, those of the granulocytic and erythrocytic series) showed insignificant staining compared with lymphocytes. Rabbit antisera used in these studies were raised to purified serum IgM of C. auratus. The serum IgM of C. auratus and C. carassius expressed identical determinants as recognized by this antibody in radioimmunoassay, but with a lower level of expression on the IgM of C. carassius. Similarly, with the use of these reagents in quantitative cytofluorometry, the lymphoid cells of C. carassius stained less brightly than those of C. auratus. However, in both species, a hierarchy of fluorescence intensity could be observed, such that spleen ? head nephros > thymus. A small percentage of lymphocytes in all organs of both species bound either myoglobin, keyhole limpet hemocyanin, or horse spleen ferritin antigens. All antigen-binding lymphocytes were also positive for membrane Ig. Analysis of the distribution of antigen and Ig patches on these cells showed that antigen patches were always coincident with Ig patches. These results provide further evidence of lymphoid heterogeneity in the genus Carassius, and are compatible with the suggestion that lymphocyte surface Ig functions as a primary recognition molecule for all lymphocytes in Carassius species.     

The development of primary and secondary lymphoid tissues in the nurse shark Ginglymostoma cirratum: B-cell zones precede dendritic cell immigration and T-cell zone formation during ontogeny of the spleen

Secondary lymphoid tissue and immunoglobulin (Ig) production in mammals is not fully developed at birth, requiring time postnatally to attain all features required for adaptive immune responses. The immune system of newborn sharks - the oldest vertebrate group having adaptive immunity - also displays immature characteristics such as low serum IgM concentration and high levels of IgM1gj, an innate-like Ig. Primary and secondary lymphoid tissues in sharks and other cartilaginous fish were identified previously, but their cellular organization was not examined in detail. In this study of nurse shark lymphoid tissue, we demonstrate that the adult spleen contains well-defined, highly vascularized white pulp (WP) areas, composed of a central T-cell zone containing a major histocompatibility complex (MHC) class II+ dendritic cell (DC) network and a small number of Ig+ secretory cells, surrounded by smaller zones of surface Ig+ (sIg+) B cells. In neonates, splenic WPs are exclusively B-cell zones containing sIgM+-MHC class IIlow B cells; thus compartmentalized areas with T cells and DCs, as well as surface Ig novel antigen receptor (sIgNAR)-expressing B cells are absent at birth. Not until the pups are 5 months old do these WP areas become adult-like; concomitantly, sIgNAR+ B cells are readily detectable, indicating that this Ig class requires a 'mature immune-responsive environment'. The epigonal organ is the major site of neonatal B lymphopoiesis, based on the presence of developing B cells and recombination-activating gene 1 (RAG1)/terminal deoxynucleotidyl transferase (TdT) expression, indicative of antigen receptor rearrangement; such expression persists into adult life, whereas the spleen has negligible lymphopoietic activity. In adults but not neonates, many secretory B cells reside in the epigonal organ, suggesting, like in mammals, that B cells home to this primary lymphoid tissue after activation in other areas of the body.     

Differentiation in the murine B cell lymphoma I.29: inductive capacities of lipopolysaccharide and Mycoplasma fermentans products

Cells from the murine B lymphoma I.29, expressing IgM or IgA of identical idiotype, were found inducible by lipopolysaccharide to differentiate into plasma cells. Within 3 days, differentiating cells lost membrane-bound immunoglobulin (Ig) and accumulated large quantities of intracytoplasmic Ig. At day 6 of culture, IgA secretion increased 50-100-fold, as determined by enzyme-linked immunoassay. Proliferation increased for the first days of culture but decreased thereafter; by day 10 very few viable cells were present in lipopolysaccharide-stimulated cultures. Similar results were obtained by culturing I.29 cells in the presence of supernatants of certain B cell lines (e.g. BFO.3). The finding of a strict correlation between the inductive activity and presence of contaminating Mycoplasma fermentans suggested that factor(s) released by mycoplasma were responsible for the mitogenic activities. This was further indicated by the findings that: the supernatants of BFO.3 that were rendered free of mycoplasma were not inductive, and a nonactive cell line could be made active by infection with supernatants of BFO.3 cells containing viable microorganisms. Thus, supernatants of mycoplasma-infected cell lines may act as potent polyclonal activators on both normal and malignant B lymphocytes. The ability to induce membrane Ig on 70Z/3 cells indicates that mycoplasma-related mitogens are also active on pre-B cells. The possibility of mycoplasma contamination should thus be carefully excluded when presumptive factors of cloned cell lines are being evaluated.     

DNA immunization in relB-deficient mice discloses a role for dendritic cells in IgM → IgG1 switch in vivo

A single intraspleen inoculation of plasmid DNA coding for an immunoglobulin heavy chain gene initiates immunity and establishes immunologic memory against the antigenic determinants of transgenic immunoglobulins, somatic transgene immunization. During priming mice produce IgM but not IgG1 antibodies. Since IgM → IgG1 class switch occurs spontaneously during the primary immune response to protein antigens we investigated possible mechanisms for failure of spontaneous isotype switch in vivo in this model of immunity. We found that inoculation of plasmid DNA in the form of a chimeric gene coding for granulocyte-macrophage colony-stimulating factor (GM-CSF) was able to drive IgG1 class switch readily after priming. Since GM-CSF activates cells of the dendritic lineage we tested the possibility that dendritic cells (DC) may be involved in regulating IgM → IgG1 switch. To this end we used bone marrow chimeras constructed from mice carrying the null mutation for the relB member of the NF-κB/Rel family as these mice lack bone marrow-derived mature DC. RelB (-/-) mice and (-/-) bone marrow chimeras inoculated with DNA/GM-CSF did not produce IgG1 antibodies during the primary immune response. Since relB (-/-) bone marrow chimeras lack DC of donor origin but possess resident follicular dendritic cells we conclude that Ig class switch in vivo is regulated by the function of interdigitating dendritic cells (IDC). Thus, IDC may contribute to the qualitative aspects of the emerging immune response.     

Identification of a Subset of Common Variable Immunodeficiency Patients with Impaired B-Cell Protein Tyrosine Phosphorylation

The mechanisms responsible for common variable immunodeficiency syndrome (CVID) are as yet unknown. In the present study, we show that the B-cell dysfunction in a subset of CVID patients is caused by defective protein tyrosine phosphorylation (PTP). We demonstrated that the PTP level and immunoglobulin (Ig) secretion malfunctions can be successfully repaired when normal plasma membrane components are implanted into these patients’ B cells. Stimulation of CVID patients’ peripheral blood mononucleated cells with anti-Ig antibody revealed that 7 of 11 patients had lower PTP levels than those found in the normal donor cells. Plasma membrane implantation to the cells of these patients resulted in elevated PTP levels which reached normal levels upon stimulation with anti-human Ig antibody. The results revealed two distinct groups of CVID patients. The first group included patients whose B cells expressed low PTP levels after Ig stimulation. In these patients the plasma membrane implantation restored the normal PTP level as well as the ability to secrete IgM and/or IgG after B-cell stimulation. In the second group, patients whose B cells expressed a normal PTP level after Ig stimulation, with no restoration of their ability to secrete Ig upon plasma membrane implantation and lipopolysaccharide stimulation. We conclude that the first group has an early signal transduction defect located in the B-cell plasma membrane, while in the second group the defect is located elsewhere.     

Differential sensitivity of B lymphocyte populations to IgM receptor ligation is determined by local factors

Ligation of surface IgM on B cells responding to lipopolysaccharide (LPS) suppresses terminal differentiation and high-rate Ig secretion with no effect on proliferation. As shown here, different B cell populations show characteristic mean values of ligand concentration required for 50% inhibition, with Gaussian distributions of sensitivity to IgM receptor ligation that reflect cellular heterogeneity of 'al-or- none' inhibitions in single cells. Differential sensitivity of B cell populations to IgM ligation seems to be locally determined by the cellular environment and unrelated to the 'maturity' of the responding cells. Thus, while long-lived peritoneal B cells are 3- to 5-fold more resistant than splenic B cells, there is no difference in sensitivity between short- and long-lived B cells in the spleen. Furthermore, while B cells in bone marrow and spleen differ in sensitivity by two orders of magnitude, B cells differentiated in vitro from bone marrow pre-B cells are as resistant as splenic B cells. Moreover, bone marrow cell culture supernatants restore a high level of sensitivity in such cell populations. Differential sensitivity to IgM receptor ligation is reproduced by multivalent nominal antigen, in cell populations that show identical dose-response inhibition curves to direct activation of protein kinase C by phorbol esters. We conclude that the level of sensitivity to IgM ligation is independent of the life span or maturity of the B cell, but differentially regulated in vivo by putative tissue factors.