2,4-Dinitrophenyl (DNP)-specific continuous B cell lines as a model system for studying B cell activation and tolerance

Effect of biphenyl dimethyl dicarboxylate on the humoral immunosuppression by ethanol

The present study was undertaken to investigate the effect of biphenyl dimethyl dicarboxylate (PMC) on the humoral immunosuppression by ethanol (EtOH) in ICR mice. PMC at a dose of 6 mg/kg was orally administered to mice daily for 28 consecutive days, and the control mice were given vehicle. Mice treated with EtOH were given freely with 20% EtOH instead of water. The results of this study are summarized as follows; a gain of body weight and the relative weights of spleen and liver were significantly increased by combination of PMC and EtOH, as compared with those in mice treated with EtOH alone. Splenic plaque forming cells (PFC) and hemagglutination (HA) titers to sheep red blood cells (SRBC), and the secondary IgG antibody response to bovine serum albumin (BSA) were decreased by the treatment of EtOH alone, then restored to normal level by PMC treatment. The elevations of serum glutamic-pyruvic transaminase (S-GPT) and total protein levels caused by EtOH were reduced to normal level by the combination of PMC and EtOH. In addition, lower serum albumin and A/G ratio were also increased to normal level. These findings indicate that PMC has a protective effect against EtOH-induced humoral immunosuppression.

Alcohol can inhibit effect of IL-4 on activated murine B cells

Ethanol addition to B lymphocytes in vitro inhibits antigen-induced antibody secretion and antigen-induced cell proliferation. We tested the hypothesis that ethanol can inhibit the effect of interleukins on B-cell proliferation by adding ethanol to in vitro functional assays for IL-2 and IL-4. Ethanol does not inhibit IL-2-induced B-cell differentiation, but it does inhibit IL-4-induced B-cell proliferation and IL-4-induced Ig class switching.

Presence of human chromosome 1 with expression of human decay-accelerating factor (DAF) prevents lysis of mouse/human hybrid cells by human complement

Xenogeneic organs transplanted to phylogenetically distant species are subject to rapid destruction mediated by complement. In humans, the complement activation is regulated by several proteins encoded by a series of closely linked genes (RCA locus) located on chromosome 1. The mouse/human hybrid cell line B10 was found to have retained human chromosome 1. FACS analysis confirmed that RCA products such as decay-accelerating factor (DAF) were expressed on the membrane surface of B10 cells. When exposed to human or rabbit complement in the presence of 'naturally occurring' human anti-mouse antibodies these cells were not lysed by human complement but were killed by rabbit complement. This effect could be abrogated by addition of anti-DAF monoclonal antibody (IC6). The results offer potential for genetic manipulation of the human complement regulatory products in animals to overcome xenograft hyperacute rejection.

B cell hyperactivity in autoimmune continuous B cell lines

Generalized increase in immunoglobulin secretion, which is a prominent feature of autoimmune diseases, may be due to abnormal T cell regulation, intrinsic abnormality of B cells, or both. To investigate this question we developed nonmalignant continuous B lymphocyte lines from 20-week-old BWF1 mice and compared their growth and immune response to that of BALB/c mice cell lines. The B cell lines contain less than 1% T cells and macrophages and require growth factors from phytohemagglutinin-stimulated EL-4 lymphoma (GF) or recombinant interleukin 4 for continuous growth. No antigens or mitogens are required for growth. In the presence of 20% GF (which is optimal for BALB/c cell growth and immune function) spontaneous growth of BWF1 B cells, and spontaneous entry into G1, was similar to that of BALB/c B cells. With concentrations of GF and anti-mu which were optimal for BALB/c, the growth and immune response of isolated BWF1 B cells are no different from those of BALB/c controls, but at suboptimal doses of GF there is a significant increase of both spontaneous immunoglobulin secretion and response to anti-mu in BWF1 B cells. Thus, these autoimmune B cells are more sensitive to the effects of both T cell factors and immunoglobulin receptors stimulation.

Immunologic tolerance to DNA in B cell lines from both normal and autoimmune mice

We examine whether B cell lines enriched for DNA specificity from either autoimmune (BWF1) or normal mice (Balb/c) can be rendered unresponsive to autoantigen in terms of the specific suppression of direct antibody-forming cells to DNA. These B cell lines were both Lyt-1 positive and negative. Preincubation with oligonucleotide, covalently linked to mouse gamma-globulin, specifically suppressed the antigen-driven response elicited by DNA horse red blood cells in B cell lines from both strains of mice. There is a 5-fold difference in susceptibility to DNA-specific tolerance induction between B cell lines of BWF1 and Balb/c mice. Thus, B cells from autoimmune mice do not appear to have an inherent absolute defect in being rendered tolerant to autoantigen, but are relatively less susceptible to DNA-specific tolerance than nonautoimmune cell lines.

Mechanisms of alcohol-induced suppression of B-cell response

Several investigators have shown that alcohol can suppress the production of antibodies by animals and humans. The studies reported here were designed to determine whether alcohol has a direct effect on the B-lymphocyte and to determine which stage of the B-cell response is inhibited by alcohol. B-lymphocyte lines specific for the antigen dinitrophenyl were used to study the effect of alcohol on the B-lymphocyte. As little as 100 mg% of alcohol inhibited the response of these pure B-cell lines to stimulation by either antigen (dinitrophenyl-Ficoll) or anti-mu antibody. Since no other cell types were present in the system the suppressive effect was on the B-cell itself. However, alcohol did not inhibit membrane depolarization induced by antigen crosslinking of immunoglobulin receptors, and it did not inhibit activation of the phosphatidyl inositol pathway by receptor crosslinking. When alcohol was added to antigen stimulated B-lymphocyte lines for varying periods during the immune response it was found that antibody production was inhibited if 150 mg% alcohol was present from 30 to 48 hr after the antigen was added to lymphocytes. Thirty-six to 48 hr is the time required for a stimulated mature B-lymphocyte to enter the proliferative phase of the immune response. These data raise the possibility that low doses of alcohol can inhibit antigen-induced B-cell proliferation.

Investigations of intrinsic abnormalities in DNA-specific B lymphocytes from autoimmune mice

In murine models of systemic lupus erythematosus and in many humans with SLE, antibodies against native DNA (dsDNA) are a major contributor to the pathogenesis of the disease. Loss of self-tolerance to the DNA antigen may be associated with B-cell defects or regulatory cell dysfunction. We have developed B-cell lines with specificity for the antigen DNA, from both the autoimmune BWF1 mouse strain and from the non-autoimmune BALB/c strain, to use in the investigation of inherent B-cell defects in autoimmunity. Six BWF1 cell lines and five BALB/c cell lines which are free of Thy1.2+ cells and esterase positive cells, and have between 35 and 89% rosetting with dsDNA-SRBC targets, have been propagated in vitro for 24-36 months. The cells are non-malignant, growth-factor dependent and have no antigen or mitogen in the growth medium. Lyt-1 positive cells are found in the cell lines, but Lyt-1 negative cells are also present. They respond to the antigen DNA-HRBC when EL-4 supernatant is present in culture, and the peak of the plaque-forming cell (PFC) response is the same for both strains. When cells from both strains are cultured with varying amounts of T-cell factors, there is no difference in spontaneous antibody-forming cell (AFC) formation or in response to anti-mu stimulation between BWF1 and BALB/c strains. BALB/c spleen cells do not respond to DNA-HRBC in this culture system, but BWF1 spleen cells, as well as cell line cells from both strains, respond to this antigen. T cells from non-responding BALB/c spleen and responding BWF1 spleen are able to suppress the immune response to DNA-HRBC of cell line B cells from both strains. Propagating B-cell lines in the presence of DNA for 2 weeks stimulates BWF1 cell line cells, but suppresses the response of BALB/c cell lines to antigen.

The role of cytoplasmic free calcium concentration in B-cell tolerance

Calcium is an important factor in the immune response. Extracellular calcium is required for antibody production by B lymphocytes. Several investigators have demonstrated that crosslinking of receptors on B lymphocytes by anti-mu antibody induces an increase in intracellular calcium. There are few data on the role of intracellular calcium mobilization or calcium influx in tolerance induction in B cells. We studied changes in free intracellular calcium concentration ([Ca+2]i) induced by exposure of dinitrophenyl (DNP)-specific B cells to the tolerance-inducing conjugate DNP-murine IgG2a (DNP-MGG). Splenic B cells enriched for DNP-specific cells and DNP-specific continuous B-cell lines were used for the studies. Exposure of B cells to the tolerogen DNP-MGG, the antigen DNP-keyhole limpet hemocyanin (DNP-KLH), or the antigen DNP-Ficoll induced an increase in free [Ca+2]i which was due to both mobilization of Ca+2 from endoplasmic reticulum (ER) and influx of extracellular Ca+2. This increase was DNP specific since no significant change was seen with carriers alone and no change was seen in cells that were not DNP specific. The DNP-MGG and DNP-Ficoll induced the same amount of Ca+2 release from ER but the release induced by DNP-KLH was higher. When B cells, which were made tolerant by in vitro incubation with DNP-MGG, were incubated with antigens, a mobilization of Ca+2 from endoplasmic reticulum occurred that was the same as that of nontolerant B cells. Since Ca+2 mobilization is associated with Ig receptor-dependent early B-cell activation, it is likely that the tolerant B cell can still receive an activation signal through the Ig receptors.

Inositol phospholipid and intracellular calcium metabolism in B lymphocytes stimulated with antigen

Stimulation of B lymphocytes by anti mu antibody can activate the phosphatidylinositol pathway, but B cell activation by LPS does not involve this pathway. This study was done to determine if stimulation of B lymphocytes by their specific antigen involves this important activation pathway. We showed that levels of IP2 and IP3 increase while PIP and PIP2 decline when dinitrophenyl specific B lymphocytes are stimulated with the antigen DNP-Ficoll. Intracellular calcium concentration also increases with this stimulus. Thus, antigen stimulation of B lymphocytes is associated with activation of phosphatidylinositol pathway.

Defects in antigen-specific immune tolerance in continuous B cell lines from autoimmune mice

B cell hyperactivity and resistance to tolerance induction are well-recognized immunologic abnormalities associated with both human and murine models of systemic lupus erythematosus. Studies evaluating the role of B cells in these defects have been complicated by the difficulties of consistently isolating large numbers of B cells from T cells and other host-derived regulatory factors. We have recently developed continuous cell lines of B lymphocytes with a high degree of specificity for the antigen dinitrophenyl (DNP) from both New Zealand black times New Zealand white F1 hybrid (BWF1) and BALB/c mice, and we used them to study intrinsic B cell defects in autoimmunity. We found that the kinetics of the immune response to the antigen DNP-Ficoll of both the BWF1 and BALB/c B cell lines are not different. In addition, the BWF1 cell lines, like the BALB/c cell lines and normal B cells, require nonspecific T cell-derived factors as well as antigen to produce an immune response. Tolerance was tested in the BWF1 B cells by preincubating them with DNP-murine IgG2a (MGG), which can induce tolerance in BALB/c cell line lymphocytes. The BWF1 B cell lines were resistant to tolerance induction by DNP-MGG and required 50-fold higher dose of DNP-MGG than BALB/c cell lines for suppression. They were also relatively resistant to tolerance with trinitrophenyl-d-glutamyl lysine. Thus, DNP-specific B cells from autoimmune mice have an inherent defect in tolerance induction.

An in vitro model for clonal anergy in continuously growing antigen-specific B-cell lines

Two continuously growing nonmalignant B-cell lines specific for the hapten DNP have been used to study tolerance in developing B cells. These cell lines have previously been shown to consist of small cells without sIgM but with cytoplasmic mu chains, and mature sIgM- and sIgD-bearing cells. When the sIgM-negative cells are placed in culture, mature DNP-specific B cells begin to appear. The studies reported here have shown that when these cell lines were propagated in the presence of either 200 micrograms/ml or 1 mg/ml of the tolerogen DNP-MGG there was no inhibition of cell line growth as measured by thymidine incorporation, and no inhibition of receptor expression by maturing B cells. The cell line lymphocytes propagated in the presence of 200 micrograms/ml DNP-MGG for 7, 30, 45, or 60 days became tolerant and the tolerance persisted for at least 6 days after removal of DNP-MGG. However, tolerance was lost between 6 and 10 days after removal of DNP-MGG. Propagation of the cell lines for 30 days in either DNP-KLH or DNP-Ficoll produced the same results. Limiting dilution cultures of cell line lymphocytes made tolerant by growing them for 30 days in the presence of DNP-MGG demonstrated that there was a marked decrease in precursor frequency compared to controls. However, cell line lymphocytes made tolerant by a 48-hr incubation with DNP-MGG did not have a significant decrease in precursor frequency. These data suggest that tolerance induced by growing these cell lines in the presence of DNP-MGG is a valid in vitro model of tolerance in developing antigen-specific B cells. Tolerance induced in this model is consistent with the clonal anergy hypothesis, but requires the continued presence of DNP-MGG to maintain unresponsiveness. This suggests that clonal anergy can occur in B cells but may not be the sole mechanism of self tolerance for those antigens which are sequestered from the immune system.