Role of gamma-interferon in antibody-producing responses

Recombinant interferon-gamma in the treatment of systemic sclerosis

PURPOSE

Recombinant interferon-gamma (IFN-gamma) is a potent and selective inhibitor of collagen production by dermal fibroblasts in vitro and has numerous immunoregulatory activities. We assessed the effects of recombinant IFN-gamma in the treatment of patients with systemic sclerosis.

PATIENTS AND METHODS

Ten patients entered the study and nine completed the six-month study period. Recombinant IFN-gamma was administered once daily for seven days per week by intramuscular injections: 10 micrograms/day for 10 days, 25 micrograms/day for 10 days, 50 micrograms/day for 10 days, and 100 micrograms/day for the next five months.

RESULTS

After the six-month treatment period, a significant improvement, as compared with base-line values, was observed in total skin score, maximal oral opening, range of motion of wrists and elbows, grip strength, functional index, dysphagia, and creatinine clearance. No serious side effects were observed; however, a significant decrease in white blood cell counts and in peripheral blood lymphocytes was noted.

CONCLUSION

These results suggest that recombinant IFN-gamma may be beneficial in the treatment of patients with systemic sclerosis.

Detection of individual interleukin 4- and gamma interferon-producing murine spleen cells after activation with T-cell mitogens

Murine spleen cells were activated with concanavalin A (Con A), pokeweed mitogen (PWM), or phorbol myristate acetate (PMA) and the calcium ionophore A23187. Cells producing gamma interferon (IFN-gamma) or interleukin 4 (IL-4) could be detected by lymphokine-specific monoclonal antibodies and indirect immunofluorescence. The frequency and kinetics of the lymphokine-producing cells were examined and were approximately the same after stimulation with Con A or PMA and A23187. Thirty hours after activation, 3-9% of the cells produced IFN-gamma. There were few IL-4-producing cells, and the maximal frequency was 1 out of 400 spleen cells 48 h after activation. When the cells were activated with PWM, the frequency of IFN-gamma-producing cells was still high 72 h after culture. The majority of the IFN-gamma-producing cells were CD8+ and expressed receptors for IL-2.

The effects of bacterial lipopolysaccharide, anti-receptor antibodies and recombinant interferon on mouse B cell cycle progression using 5-bromo-2'-deoxyuridine/Hoechst 33258 dye flow cytometry

Polyclonal stimulation of resting B cells with anti-antigen receptor antibodies [anti-IgM mu chain antibody (anti-mu)] or with bacterial lipopolysaccharide (LPS) stimulates a proportion of B cells to proliferate. Exposure of resting B cells to both LPS and anti-mu activates a larger population of resting B cells than either alone, suggesting a synergistic effect of these two stimuli. Although recombinant interferon (rIFN) either alone or in combination with anti-mu has no apparent proliferative activity (as measured by [3H]thymidine incorporation), application of 5-bromo-2'-deoxyuridine/Hoechst 33258 dye flow cytometry reveals a distinct effect of rIFN on B cell growth. In the presence of anti-mu plus LPS, rIFN causes the majority of B cells to enter the cell cycle (CC), but a subset of B cells remains in the resting stage. Another subset of B cells has extremely rapid CC transit times, with a CC duration of less than 10 h. These studies show that both anti-mu and LPS are competence factors (which move cells from the G0 phase to the G1 phase). LPS acts also as a CC progression factor, while rIFN is a CC potentiating factor.

Demonstration and partial characterization of the interferon-gamma receptor on human B lymphocytes

The expression of interferon-gamma (IFN-gamma) receptors on normal human B cells and four B cell lines was studied. Recombinant human IFN-gamma was labeled with [gamma-32P]ATP using the catalytic subunit of a cAMP-dependent protein kinase. All four B cell lines, although differing in their responsiveness to IFN-gamma, were found to express high-affinity receptors (1,000-11,000 receptors/cell). Normal unactivated B lymphocytes were also found to express constitutively high-affinity receptors, approximately 1,400 receptors per cell with an estimated affinity of 295 pM. Activation of the normal B cells in vitro with the polyclonal B cell activator, Staphylococcus aureus Cowan strain I (SAC), resulted in a slight decline in receptor number and a more pronounced fall in receptor density. One of the B cell lines and unactivated normal B cells were shown to internalize labeled IFN-gamma rapidly. Chemical cross-linking of 32P-IFN-gamma to the CB B cell line and to freshly isolated B lymphocytes revealed one major cross-linked receptor-ligand complex which had an estimated molecular weight of approximately 110 kilodaltons. This complex corresponded to a 93 kD receptor cross-linked to recombinant IFN-gamma. Our data indicate that normal B lymphocytes constitutively express an approximately 93 kD IFN-gamma receptor which is similar to the receptor present on Epstein-Barr virus-transformed B cell lines.

PHA-induced interferon in multiple sclerosis: association between gamma interferon and clinical and genetical variables

Gamma interferon (INF-gamma) production, after PHA stimulation of peripheral blood mononuclear cells, from multiple sclerosis (MS) patients with the acute remitting and chronic progressive forms, in attack and remission phases, and from normal controls, was studied by immunoradiometric assay. MS patients in all these 4 clinical states of disease produced less INF-gamma (log value range from 2.55 to 2.65). MNC from the total MS patients produced significantly low levels of INF-gamma compared to the control group (log values 2.60 vs. 2.82; P = 0.001). No association between the interferon production and antigens at any HLA locus (A, B, C, Dw and Bf) was found. There was no correlation between IFN-gamma production and age, sex, duration of disease, or disability index. However there was a slight tendency to negative correlation with the progression index of the disease. The results suggest that this lower IFN-gamma production in MS may be secondary to the disease, and the primary defect may be a severe reduction of the essential lymphocyte populations required for an effective lymphokine cascade to produce the normal immune response against infection.

Aging-associated intrinsic defects in IgA production by murine Peyer's patch B cells stimulated by autoreactive Peyer's patch T cell hybridoma-derived B cell stimulatory factors (BSF)

Immune functions deteriorate with age, primarily as a result of alterations in the number and subpopulations of T cells of the immune system. In contrast, the B cell component of the immune system is generally affected by senescence only to a minor extent. In the present report, we stimulated murine Peyer's patch (PP) B cells by nonspecific multifunctional B cell stimulatory factors (BSF) secreted by one of several autoreactive (self-major histocompatibility complex (MHC)-class II antigen-responsive) T cell hybridoma clones derived from PP of syngeneic mature adult mice, and then determined in vitro whether aging-associated intrinsic defects could be demonstrated in the proliferation of, and the synthesis and secretion of mucosal IgA by, the BSF-activated B cells. This approach could be a useful new in vitro method for assessing the effect of senescence on B cell Ig production, especially that of IgA, in the gut-associated lymphoid tissue (GALT). Aged PP B cells stimulated by the autoreactive PP T cell-derived BSF proliferated more (P less than 0.05), contained larger amounts of IgA (nearly 10 times) and also secreted considerably more IgA (nearly 4.5 times) than did mature adult PP B cells. However, the ratio of intracellular dimeric (d) IgA to total IgA in the aged B cell lysates was significantly reduced (by approx. 44%) as was also the secreted dIgA (by approximately 50%). The augumentation of not only the proliferation, but also the synthesis and secretion of IgA in vitro along with reduced dIgA/total IgA ratios of BSF-stimulated aged PP B cells appears to be due to aging-related intrinsic defects. Alterations in intracellular regulatory mechanisms of B cells, mediated by B cell receptors for autoreactive T cell-derived BSF, could be largely responsible for the observed polyclonal B cell hyperreactivity, associated with senescence.

The immunomodulatory effects of interferon-gamma on mature B-lymphocyte responses

Interferon-gamma (IFN-gamma) exerts a broad spectrum of activities which affect the responses of mature B-cells. It strongly inhibits B-cell activation, acts as a B-cell growth factor (BCGF), and also induces final differentiation to immunoglobulin (Ig) production. IFN-gamma is deeply involved in the differential control of isotype expression, as it enhances IgG2a production and suppresses both IgG1 and IgE production. Although it is now possible to draw a general scheme of the effects of IFN-gamma on B-cells, a number of paradoxical results still exist in the field. In this manuscript, different experimental systems are analyzed in an attempt to explain these apparent paradoxes.

Enhancement of primary and secondary immune responses by interferon-gamma

We have investigated the effects of interferon-gamma (IFN-gamma) administered with "G" glycoprotein of vesicular stomatitis virus (VSV), on the neutralizing antibody response. Treatment of mice or cattle with recombinant DNA-derived IFN-gamma at the time of primary immunization with "G" glycoprotein enhanced the secondary virus-neutralizing antibody response that followed a booster administration of the same antigen without IFN-gamma treatment. Enhancement was statistically significant, and occurred at relatively low doses of IFN-gamma in the absence of any additional adjuvants. Cattle treated with IFN-gamma at the time of primary immunization were also more resistant to VSV challenge than those immunized without IFN-gamma treatment. Such treatment in conjunction with primary immunization may therefore provide a practical means of enhancing protection from viral challenge without inflammatory adjuvants or boosters.

Growth factors in haemopoiesis

Haemopoietic growth factors have for over two decades allowed experimentalists to grow haemopoietic bone marrow cells in vitro. With refinements in technique and the discovery of novel growth factors, all of the known haemopoietic lineages can now be grown in vitro. This has allowed a much greater understanding of the complex process of haemopoiesis from the haemopoietic stem cell to the mature, functioning end-cell. The in vivo action of these growth factors has been harder to investigate. Although recombinant technology has afforded us the much greater quantities necessary for in vivo work, problems remain with administration because of effects on other tissues. Interpretation of results is difficult because of the complex inter-relationships which exist between factors. Some of these have been defined in vitro and it appears likely that they also operate in vivo. Erythropoietin is a physiological regulator of erythropoiesis. It has been detected in vivo with levels responding appropriately to stress (i.e. elevated in anaemia) and, when administered in pharmacological doses, has been shown to correct anaemia. Granulocyte/macrophage colony-stimulating factor (GM-CSF) has been detected in vivo and may influence the production and function of granulocytes and macrophages, although how it is regulated is unknown. Granulocyte colony-stimulating factor (G-CSF) and macrophage colony-stimulating factor are ore lineage-specific. Interleukin 3 (IL-3), although it has not been detected in vivo, may act on a primitive marrow precursor by expanding the population and making these cells more susceptible to other growth factors, such as GM-CSF. Interleukin 1 (IL-1) has been detected in vivo, does not appear to have any isolated action on bone marrow (except possibly radioprotection) but probably acts synergistically with other growth factors, such as G-CSF. Interleukins 2, 4, 5 and 6 have not been detected in vivo. All have effects on B-cells. In addition IL-2 is an essential factor for the in vitro growth of T-cells and may have antitumour effects in vivo. IL-5 is an eosinophil growth factor in vitro. Megakaryocytopoiesis is also affected by humoral factors. Factors, alone or in combination, may be useful to restore functional granulopoiesis when used therapeutically. Some can be used as anticancer agents, although there may be a risk of induction of haematological malignancy. Increased understanding of their physiological roles will allow a more rational use.

Human hybridoma suppressor factor (HSF) inhibits IL2 production in addition to suppressing immunoglobulin production

The human thymus cell hybridoma, 8E-24, secretes a potent immunosuppressive factor(s), HSF, which inhibits polyclonal immunoglobulin (Ig) production. Our current studies reveal that this suppression is monocyte dependent in that its suppressive activity for Ig production was not observed in monocyte-depleted lymphocyte cultures but was restored by addition of monocytes. The requirement for monocytes was equally satisfied by autologous or allogeneic monocytes or monocyte conditioned media. Although the suppression mediated by HSF required the presence of monocytes, the mechanism for monocyte participation appears to be different from that reported for suppression mediated by soluble immune response suppressor (SIRS) in that general oxygen free radical scavengers did not inhibit this activity. Further information on the mechanism of action of HSF was obtained from studies on its suppressive effect on the phytohemagglutinin(PHA)-induced proliferative response. In this system HSF significantly suppressed PHA induced interleukin 2(IL2) production of peripheral blood mononuclear cells (PBMC) in a dose dependent fashion without inhibiting the proliferative response of CTLL-20 target cells to IL2. Interleukin 1 (IL1) production by monocyte cultures was also not suppressed by HSF. These results indicate that HSF interferes with IL2 production and not its induction by IL1 or its interaction with the IL2 receptor. To investigate the role of HSF-induced IL2 suppression in the pokeweed mitogen (PWM) antibody synthesis assay, the time course of IgG, IgM, IL1, and IL2 production of PWM stimulated PBMC cultures was examined. Results showed that the peak of IL2 production occurred on the second day of culture and was significantly suppressed by HSF while IL1 production was not affected during the seven day culture period. Similar suppression of IL2 and IgM production was observed in cultures of B cells and T4+ cells. Reconstitution of the IL2 levels in these cultures with recombinant IL2 completely restored antibody production. These results suggest that HSF in the presence of monocytes modulates the function of T4+ cells by inhibiting IL2 production. The inhibition of IL2 production by HSF appears to be responsible for the suppression of antibody production.

Glucocorticosteroid-dependent synergy between interleukin 1 and interleukin 6 for human B lymphocyte differentiation

In order to analyze the effects of interleukin (IL) 6 on human in vitro Ig production B lymphocytes were activated by Staphylococcus aureus Cowan strain I (SAC) in the presence of low concentrations of IL2 (1 U/ml) and dexamethasone (10(-7) M). Previously we showed that this model of B cell response is completely monocyte dependent. We here demonstrate that, under these experimental conditions, IL6 is able to replace monocytes and stimulate Ig production provided IL1 is also present. Dose-effect curves show that these two monokines act synergistically. This synergy is demonstrable only in the presence of dexamethasone, when B lymphocytes are activated (by SAC) and when T cell help (provided by IL2) is present. It results in the production of both IgM and IgG. Both IL1 and IL6 have to be present during the first 48 h of culture to exert an optimal effect. These results show that IL6 may act on early (as well as on late) stages of normal B lymphocyte differentiation. Moreover, glucocorticosteroids potentiate the synergistic effect of IL1 and IL6 on their B lymphocyte target, an effect comparable to that exerted on hepatocytes.

Generation of high-rate ovalbumin-specific antibody-secreting cells in cultures of human peripheral blood B cells obtained from non-immunized blood donors

When human peripheral blood B cells are cultured for 6 days with the T cell-dependent peptide antigen ovalbumin (OA) in the presence of antigen-presenting cells and helper T cells, plaque-forming cells (PFC) are generated. These OA-induced PFC differ from the conventional high-rate antibody-secreting PFC formed after stimulation of B cells with recall antigens (e.g. tetanus toxoid) in that they secrete antibody at a very low level. Previous studies have shown that OA-induced PFC are B lymphocytes in an early activation state rather than cells that have differentiated into plasmablasts. The apparent arrest in the maturation of OA-induced PFC in an early activation phase can be overcome by simultaneous stimulation with interleukin 2 (IL-2) and gamma interferon (IFN-gamma). The isotype of the OA-specific antibodies secreted, however, are only of the IgM class, demonstrating that an isotype switch does not occur.

Production of gamma interferon in Mls disparate interactions

The murine T-cell clone E11 isolated from a primary H-2k histocompatible one-way mixed lymphocyte culture of B10.BR anti C3H/Tif spleen cells was used to study multidirectional interactions in strong stimulatory Mls disparate responses. Several parameters have recently been studied, and proliferation of T cells upon stimulation by macrophages or B cells of Mls-disparate stimulator cells, induction of differentiation of B cells of stimulator strains but inhibition of their macrophage differentiation, and the inhibition by E11 T cells of the production of a mitogenic mediator by Mls-disparate spleen cells have been found. As shown in this paper, these phenomena can be explained by an Mlsa, d, e specific induction of gamma-interferon (IFN-gamma) production in the responder B10.BR (Mlsb) E11 T cells. It is suggested that IFN-gamma, as a regulator of feedback mechanisms plays a critical role in Mls disparate T-cell stimulation.

Effect of recombinant human interleukin 4 on spontaneous in vitro human IgE synthesis

Recombinant human interleukin 4 (IL 4) alone enhanced the spontaneous IgE synthesis in cultures of peripheral blood leukocytes (PBL) from atopic patients as well as from nonatopic individuals, suggesting the existence of preactivated PBL sensitive for IL 4. Preactivated cells were also obtained by stimulation with Staphylococcus aureus strain Cowan I (SAC). However, co-stimulation of PBL by IL 4 with SAC or anti-IgM antibody and pokeweed mitogen did not result in an enhanced IgE synthesis. Optimal IL 4 concentrations for the induction of IgE synthesis coincided with optimal proliferative responses in PBL. The effect of IL 4 was not isotype specific, and in terms of protein even more IgG and IgM antibodies were formed. The effect of IL 4 on IgE synthesis was counteracted by very low concentrations of interferon-gamma (IFN-gamma), suggesting that both IL 4 and IFN-gamma might be decisive cytokines for the human in vitro IgE synthesis.

Reduced mortality in murine cytomegalovirus infected mice following prophylactic murine interferon-gamma treatment

Efficacy of recombinant DNA-derived murine IFN-gamma was investigated in a murine model of cytomegalovirus infection. Treatment of 3-week-old Swiss Webster mice with murine IFN-gamma prior to infection with murine cytomegalovirus (MCMV) significantly reduced mortality due to MCMV infection. Efficacy was dose-dependent and was observed using either intraperitoneal or intramuscular injection as the route of administration. Two doses, one at 24 h and one at 4 h prior to MCMV infection, were required for optimum efficacy, and doses administered after MCMV infection had no apparent effect. Reduced infectious MCMV titers were observed in critical organs of IFN-gamma treated mice and histopathologic lesions induced by MCMV infection were in general less severe and resolved sooner than lesions in untreated mice. Results in this murine model of cytomegalovirus infection suggest that IFN-gamma treatment may be useful as prophylactic therapy for human cytomegalovirus infections when a high probability of exposure to the virus exists and consequences of infection may be severe.

Ovalbumin-specific human B-cell activation and maturation. The absence of final maturation is due to the incapacity of ovalbumin-activated T cells to produce maturation factors

By means of a panel of monoclonal antibodies it is demonstrated that, in cultures of human peripheral blood mononuclear cells (PBMC) with the T-cell-dependent (TD) antigen ovalbumin (OA), responding B cells are activated from the resting state. The differentiation of the activated B cells to high rate-secreting plasma blasts, however, is arrested in an early activation phase, in which they can be detected as low rate-secreting plaque-forming cells. The arrest does not occur when stimulation with OA occurs in the presence of antigen-nonspecific activation and maturation factors, which are provided in the culture by the anamnestic response to the TD antigen tetanus toxoid.

Interferons and autoimmunity

Autoimmunity can be accelerated in several genetically prone murine models and can even be induced in normal mice by treatment with interferon (IFN) or IFN-inducers. Several cases of IFN-induced autoimmune disease in humans also have been observed; however, more striking is the fact that some of the clinical manifestations in autoimmune diseases and many of the immunological aberrations can be mediated or enhanced by IFN. The finding of high levels of circulating IFN in many patients may be highly significant in that respect, and the characterization of the predominant type of IFN as an unusual acid-labile IFN-alpha may indicate an infectious etiologic agent in autoimmunity, since this peculiar IFN was mostly associated with viral infections in vivo or in vitro. The induction of MHC class II antigens on previously HLA-DR or Ia negative cells appears to be caused primarily by IFN-gamma and may have a central role in the pathogenesis of autoimmunity in susceptible individuals. Such aberrant HLA-DR expression on nonlymphoid cells can be detected early in the disease in the target organs of many varied autoimmune conditions and may trigger a cascade of self-directed, uncontrolled immune response in conjunction with other factors.

Interferon-gamma and antibiotics fail to act synergistically to kill Legionella pneumophila in human monocytes

Legionella pneumophila, the agent of Legionnaires' disease, is a gram-negative facultative intracellular bacterial pathogen that multiplies in human blood monocytes and alveolar macrophages. Interferon-gamma (IFN-gamma)-activated human monocytes inhibit the intracellular multiplication of L. pneumophila but fail to kill the organism. Similarly, erythromycin and rifampin, the drugs of choice in the treatment of Legionnaires' disease, inhibit the growth of L. pneumophila within monocytes without exerting a cidal effect. In this study, we examined the combined effects of IFN-gamma and antibiotics (erythromycin, rifampin, and clindamycin) to determine whether these independently acting agents would synergistically mediate the killing of intracellular L. pneumophila. Each agent alone or in combination was effective in inhibiting the intracellular multiplication of L. pneumophila. However, IFN-gamma and antibiotics together were unable to kill intracellular L. pneumophila, regardless of the sequence in which they were administered to monocytes. Like erythromycin and rifampin, clindamycin, which is highly concentrated in human alveolar macrophages, was capable of inhibiting the intracellular multiplication of L. pneumophila but failed to kill the bacteria in nonactivated or IFN-gamma-activated monocytes. These results demonstrate that intracellular L. pneumophila are highly resistant to the bactericidal effects of both activated monocytes and antibiotics, alone or in combination.

Biochemical characterization and biological effects of partially purified B cell-activating factor (BCAF)

B cell-activating factor (BCAF) has been characterized and partially purified from the supernatant of the murine tumor T cell line 373. BCAF has an apparent molecular mass of 15 to 20 kDa when analyzed by Superose 12 fast protein liquid chromatography (FPLC) gel filtration and a pI of 4.5 to 5.0 when analyzed by FPLC chromatofocusing. Concentrated supernatant was applied to a nickel chelating column and unadsorbed active material was further purified by two sequential C4 reverse-phase high-performance liquid chromatography steps. This purification procedure allowed a complete separation of interleukin 2 and interleukin 4 activities from BCAF. This partially purified BCAF induces Ia expression, cell size increase and proliferation of small resting B cells. Furthermore, we have shown that the activity of partially purified BCAF is insensitive to treatment by monoclonal antibodies specific for interleukin 4 and interleukin 5.

5-Halo-6-phenyl pyrimidinones and 8-substituted guanosines: biological response modifiers with similar effects on B cells

5-Halo-6-phenyl pyrimidinones, represented by 2-amino-5-bromo-6-phenyl-4(3H)-pyrimidinone (ABPP) and 2-amino-5-iodo-6-phenyl-4(3H)-pyrimidinone (AIPP), and 8-substituted guanosines, represented by 8-bromoguanosine (8-BrGuo) and 8-mercaptoguanosine (8-MGuo), are well-documented biological response modifiers. We have found that these substituted pyrimidinones and guanosines are very similar in their abilities to activate B cells. ABPP, AIPP, 8-BrGuo, and 8-MGuo induced murine B cells to polyclonally proliferate and differentiate in vitro. The maximal B-cell response levels and the kinetics of the responses elicited with both classes of compounds were comparable; however, ABPP and AIPP were approximately 10-fold more potent than 8-BrGuo and 8-MGuo. An additional similarity observed between the two classes was that polyclonal activation of B cells by ABPP, AIPP, 8-BrGuo, and 8-MGuo was limited to large B cells which had probably been activated previously in vivo. This is in contrast to lipopolysaccharide which is capable of inducing both large, activated B cells and small, resting B cells to proliferate and differentiate. Although substituted pyrimidinones and guanosines were not able to induce new DNA synthesis or antibody production in small B cells, both classes of compounds increased the expression of Ia antigens on the surface of both small and large B cells. These data, together with the recent observations that 8-BrGuo, like ABPP and AIPP, can stimulate NK and cytotoxic macrophage activity via the induction of interferon, strongly suggest that 5-halo-6-phenyl pyrimidinones and 8-substituted guanosines belong to the same structural class of biological response modifiers. Thus, the residues held in common by these two classes of stimulators may interact with the same cellular constituent in the target cells.

Induction of human in vitro IgE synthesis via stimulation by anti-CD3 antibody

Mitogens such as pokeweed mitogen, Staphylococcus aureus Cowan I, concanavalin A and phytohemagglutinin and monoclonal anti-CD antibodies were examined for their capacity to induce IgE synthesis by peripheral blood leukocytes obtained from both atopic and nonatopic individuals. While lectins failed to induce IgE synthesis, monoclonal anti-CD3 antibodies were very potent stimuli for the induction of human in vitro IgE synthesis, possibly due to the activation of T cells. Activation via CD4 or CD8 molecules by OKT4 or OKT8 antibodies did not lead to a T cell-dependent modulation of IgE synthesis. PWM acted in synergy with the enhancing effect of anti-CD3 antibodies for IgE synthesis. In vitro IgG production was less affected. These results indicate that activation of T cell via CD3 molecules may be important in the regulation of IgE immune responses in man. Furthermore, the successful induction of IgE synthesis by anti-CD3 antibody in unfractionated peripheral blood leukocytes culture provides a simple model for investigation of human IgE regulatory mechanism in vitro.

B cell precursor growth-promoting activity. Purification and characterization of a growth factor active on lymphocyte precursors

We have used a biological assay system we developed to biochemically purify a previously uncharacterized murine lymphopoietic growth factor designated lymphopoietin 1 (LP-1). This factor is capable of stimulating the proliferation and extended maintenance of precursor cells of the B lineage. A stromal cell line producing LP-1 was established after transfection of primary stromal cultures with a plasmid encoding the transforming genes of SV40. This factor was purified to a single 25-kD species from the culture supernatant of an adherent stromal cell line. This material acts on immature lymphocytes, it binds to specific receptors on cells, and is distinct from previously described hematopoietic factors. LP-1 has been purified some 10(7)-fold with an overall recovery of 35%. The purified protein exhibits a specific activity of approximately 4 X 10(6) U/micrograms of protein and is active at a half-maximal concentration of 10(-13) M.

Interferon and phorbol esters down-regulate sIgM expression by independent pathways

We studied the effects of recombinant interferon, 12-0-tetradecanoylphorbol-13-acetate (TPA), and phorbol 12, 13 dibutyrate (PDB) on surface immunoglobulin expression by Daudi cells. Incubation of cells with recombinant alpha 2 interferon (IFN-alpha 2) caused a 2.5-fold (60%) decrease in sIgM expression as measured by relative fluorescence index (RFI) using a flow cytometer. This decrease in sIgM expression was independent of inhibitory effects on proliferation and cell cycle progression. TPA or PDB also caused a threefold (67%) decrease in sIgM expression, while enhancing proliferation and cell cycle progression. Coincubation of cells with IFN-alpha 2 and TPA decreased sIgM expression by more than fourfold (greater than 75%), which was greater than the decrease induced by the optimal concentration of either agent alone. Molecular studies demonstrated that the treatment of cells with IFN-alpha 2 or TPA decreased the steady-state levels of mRNA for the heavy chain of IgM (c mu), suggesting that down-regulation of sIgM occurred at a pretranslational level. Activation of the cell membrane sodium/proton antiport did not play an integral role in the IFN-alpha 2 or phorbol-ester-induced pathway of sIgM down-regulation. Whereas IFN-alpha 2 induced an increase in the activity of 2',5'-oligoadenylate (2-5A) synthetase, the addition of TPA to IFN-alpha 2 caused a significant decrease in the activity of this enzyme. Although IFN-alpha 2 and TPA exhibited additive effects on sIgM expression, they had opposing effects on cell proliferation, cell cycle progression, and induction of 2-5A synthetase activity, suggesting that these agents down-regulate sIgM expression through independent pathways.

Enhanced response of autoantibody-secreting B cells from young NZB/NZW mice to T-cell-derived differentiation signals

Spleen cells from young NZB/NZW mice spontaneously produce IgM antihistone and anti-DNA antibodies in culture, and this in vitro autoantibody production is T-cell dependent. In the present studies, we investigated the response of young autoantibody-producing NZB/NZW B cells to various T-cell-derived signals. Stimulation with unprimed allogeneic T cells resulted in a 10- to 20-fold increase in IgM antihistone and anti-DNA antibody production compared with cultures of B cells alone. The responding cells were found in the large B-cell fraction after separation on Percoll gradients. Allo-stimulated B cells from nonautoimmune mice produced much lower absolute amounts of IgM autoantibodies as well as total IgM compared with NZB/NZW cells. Marked IgM antinuclear antibody and total IgM production was also observed when NZB/NZW B cells were cultured with supernatants from TH2 but not TH1 T-helper clones. Although B cells from nonautoimmune mice produced high levels of autoantibodies after stimulation with lipopolysaccharide, only minimal levels were secreted in response to the active supernatants. These results suggest that young NZB/NZW mice have IgM autoantibody-producing B cells that are more sensitive to certain T-cell-derived signals compared with B cells from normal mice. Although these hyperresponsive NZB/NZW cells appear to be in an advanced stage of activation, they require additional T-cell signals to express this abnormality.

Multidirectional interactions in an Mls-disparate response

The murine T cell clone E11, isolated from a primary H-2k-histocompatible, one-way mixed lymphocyte culture of B10.BR anti-C3H/Tif spleen cells, has been used to analyse multidirectional interactions in Mls-disparate responses. Several events can be observed. There is proliferation of T cells upon stimulation by macrophages or B cells of Mls-disparate stimulator cells. In addition, one finds induction of differentiation of B cells of stimulator strains. E11 T cells inhibit spreading and differentiation of macrophages of stimulator strains and also prevent the production of a T cell growth-supporting mediator by Mls-disparate spleen cells. All these phenomena can be explained by Mlsa,d,e-specific induction of gamma-interferon (gamma-IFN) production in the responder B10.BR (Mlsb) E11 T cells. It is suggested that gamma-IFN, as a regulator of feedback mechanisms, plays an essential role in Mls-disparate cell interactions.

Increased immunoglobulin response to gamma-interferon by lymphocytes from patients with systemic lupus erythematosus

The factors responsible for abnormal B-cell activation in systemic lupus erythematosus (SLE) are incompletely understood. This study tested the hypothesis that the abnormal B-cell activation observed in human SLE may be due to an augmented response to a helper signal. We demonstrated that non-T cells from 10 of 19 SLE patients increased IgG production in response to interferon-gamma (IFN-gamma) by a mean factor of 20.9 +/- 3.9 over resting levels, while controls stimulated a mean factor of 3.0 +/- 0.5 (P less than 0.005). We found no relationship of IFN-gamma responsiveness to disease activity. Serotyping for HLA A, B, C, and D loci suggested that the hyperresponsiveness may be genetically linked to HLA-Cw7. We conclude that IFN-gamma may contribute to the development and perpetuation of SLE in a subset of patients with SLE.

Induction of IgG2a secretion from mIgG2a+ B-lymphoid tumor cells by BCDF present in several antigen-specific T-helper clones

In order to study the soluble factor(s) that play an important role for the differentiation of IgG2-secreting B cells, we examined whether membrane IgG2a (mIgG2a)-bearing BALB/c B-lymphoid tumor cells, A20, could be induced to secrete IgG2a after treatment with soluble factors. We detected a potent B-cell differentiation activity inducing the Ig secretion of A20 tumor cells (BCDF-A20) in supernatants of several soluble antigens as well as alloantigen-specific T-cell clones of various genetic backgrounds. Thus, this BCDF-A20 activity was working in an antigen-nonspecific and MHC-nonspecific manner and abundant in many T-cell clones. It was shown that neither interleukin 1, interleukin 2, interferon, T-cell replacing factor, B-cell maturation factor, nor B-cell stimulatory factor-1 alone had any significant effect on the induction of Ig secretion of A20 tumor cells. Using isotype-specific rabbit anti-mouse Ig developers, we showed that mIgG2a+ A20 tumor cells secreted IgG2a after the treatment with soluble factors. The peak of the response of A20 tumor cells to BCDF-A20 was obtained 3 days after the treatment with culture supernatants of T-cell clones. In this study, we have clearly shown that mIgG2a+ A20 tumor cells were able to secrete IgG2a after treatment with T-cell soluble factors.

A role for IFN-gamma and NK cells in immune responses to T cell-regulated antigens types 1 and 2

Responses to antigens that have been previously recognized as T cell-independent are now known to be dependent on some form of T-cell (or T cell-derived) help. This T-cell dependency, however, can be most easily noted when responses to small resting B cells are examined, since responses of larger, size-separated B cells to TNP-Ficoll require little if any T-cell help. The type of ancillary "help" that is required for the responses to type 1 and type 2 antigens exhibits certain similarities as well as differences. Thus, responses to both of these antigens can be stimulated in the presence of L3T4- or L3T4+ cells as well as in the presence of IL2. However, while the presence of IFN-gamma may be significantly inhibitory for the responses to the type 2 antigen TNP-Ficoll, they do not appear to influence the response to the type 1 antigen TNP-BA. Furthermore, while vigorous elimination of NK cell activity from purified B-cell populations enhances the response to TNP-Ficoll, it has no discernible effect on the response to TNP-BA. These results suggest that determination of type 1 and type 2 antigens may be made not only based on the characteristics of the carrier molecule but also on the nature of ancillary help that needs to be provided for these antigens to stimulate optimal responses. Type 1 antigens have polyclonal B-cell activating properties and stimulate responses which are not influenced by IFN-gamma, type 2 antigens have no polyclonal B-cell activating properties and stimulate responses which can be influenced by IFN-gamma.

B-cell activation stimulated by monoclonal anti-Lyb2.1 antibody is mediated through a receptor distinct from the BSF-1 receptor

The experiments in this paper demonstrate that monoclonal anti-Lyb2.1 antibody enhances the proliferative response of anti-immunoglobulin (anti-Ig)-stimulated but not of dextran sulfate-stimulated B cells. The magnitude of this enhanced B-cell proliferation is comparable to that induced by BSF-1 on anti-Ig-stimulated cells. The ability of this antibody to enhance B-cell proliferation does not result from its ability to neutralize the suppressive effects on B-cell activation that is mediated by the Fc fragment of anti-Ig antibody as it is equally as effective in enhancing B-cell proliferative responses stimulated by F(ab')2 fragments of anti-Ig. BSF-1 and Anti-Lyb2.1 appear to stimulate nonoverlapping pathways leading to B-cell activation since the enhanced responses induced by the combination of BSF-1 and anti-Lyb2.1 on anti-Ig-stimulated cells are additive even when maximum quantities of these activators are employed. There is also a marked difference in their activity on T cells; while BSF-1 can enhance T-cell proliferation in synergy with phorbol ester, anti-Lyb2.1 is ineffective in this regard. These data, while consistent with the suggestion that the Lyb2 surface determinant on B cells may be involved in B-cell activation, indicate that it is distinct from the receptors for BSF-1 or BCGF-II.

[Effectiveness of gamma interferon and alpha interferon in hairy cell leukemia]

Six patients with hairy-cell leukemia were treated with gamma-(IFN-gamma) and alpha-(IFN-alpha-2b) interferon; 3-35 months following splenectomy, treatment was started with 4 X 10(6) U/m2 IFN-gamma sc (iv) every second day for 9-35 weeks. Although the white blood cell counts decreased during therapy from 4.1-49 X 10(9)/l to 1.5-43 X 10(9)/l, no hematological or clinical improvement was obtained. Subsequently (interval 0-13 weeks), IFN-alpha-2b was given at an initial dose of 4 X 10(6) U/m2 sc every second day to all patients. After a treatment period corresponding to that of IFN-gamma administration, a significant hematological improvement was observed in five patients (one early death due to pulmonary embolism). At the last follow-up (9-14 months after start of treatment; maintenance therapy, 1 X 10(6) U every second day), these patients exhibited normal peripheral blood cell counts, and in bone marrow biopsy specimens a marked decrease of hairy cells was seen (1 CR, 3 PR, 1 MR). Adverse reactions including fever, headache, nausea, dryness of the mouth, myalgia, and fatigue did not significantly differ between the two interferon preparations. Whereas IFN-gamma is unlikely to have any significant impact on the course of hairy cell leukemia, IFN-alpha-2b does result in improvement of hematological values and well-being in almost all patients.

Production of a monoclonal antibody useful in the molecular characterization of murine T-cell-replacing factor/B-cell growth factor II

T-cell-replacing factor (TRF) is a T-cell-derived factor required for terminal differentiation of activated B cells to immunoglobulin-secreting cells. Previous studies have shown that a murine T-cell hybrid (B151K12) produces factor(s) that (i) induce immunoglobulin secretion by the B-cell leukemia line BCL1 and secondary anti-2,4-dinitrophenyl IgG synthesis in vitro by dinitrophenyl-primed B cells (TRF activity) and (ii) cause proliferation of the BCL1 cells [B-cell growth factor II (BCGF-II) activity]. Both activities appear to be associated with the same molecule. Here we report the production of a monoclonal antibody to murine TRF. The monoclonal antibody, designated TB13, strongly inhibited both TRF and BCGF-II activities and absorbed TRF- as well as BCGF-II-active molecules produced by B151K12 and by Xenopus oocytes that had been injected with mRNA transcribed from plasmid pSP6K-mTRF23. Inhibition was linearly dependent on the concentration of both TB13 and TRF. Monoclonal antibody TB13 did not inhibit the activities of B-cell stimulatory factor 1, interleukin 1, interleukin 2, or interleukin 3. TRF activity in dissolved samples of immunoprecipitates obtained with TB13 was recovered after NaDodSO4/PAGE, in the fractions corresponding to a protein band at Mr 46,000. Our results indicate that monoclonal antibody TB13 recognizes a molecule that has both TRF and BCGF-II activities.

T cell-derived B cell growth and differentiation factors

In the last few years it has been demonstrated that clonal expansion of B lymphocytes and their differentiation into antibody-producing cells are regulated by a complex series of soluble products released by T cells. The application of cloning and recombinant DNA techniques has made it possible to obtain most of these molecules in a purified form and, therefore, to study in more detail their functional properties. To date, three distinct T cell-derived B cell growth factors (BCGFs) and/or B cell differentiation factors (BCDFs), i.e., IL-2, IL-4 and IL-5, have been reported for mouse B cells. Likewise, at least five distinct molecules showing BCGF and/or BCDF activity (IL-2, IFN-gamma, IL-4, the 12 kD-BCGF and BSF-2) for human B cells have been identified. Human T cell-derived lymphokines active on B cells are functionally similar but not identical to murine lymphokines. Most T cell-derived lymphokines can exert their activity on the same B cells in different stages of activation and evoke different responses. In addition, some of them are not specific for B cells, but act as competence factors or competence cofactors for different hemopoietic cell lines. Finally, convincing evidence is accumulating to suggest that both activated and resting B cells may have receptors for BCGFs and BCDFs. This makes it clear why although the goal of a directed immune response is to generate antigen-specific antibodies, a large part of this response can actually be polyclonal and nonspecific.

T cell replacing factor/interleukin 5 induces not only B-cell growth and differentiation, but also increased expression of interleukin 2 receptor on activated B-cells

A T-cell replacing factor (TRF)/interleukin-5 (IL-5) is a B-cell growth and differentiation factor. In the present study, we examined the role of TRF/IL-5 in the increase in the levels of interleukin-2 (IL-2) receptor expression on activated B-cells. High pressure liquid chromatography (HPLC)-purified TRF/IL-5 (B151-TRF) from TRF-producing T-cell hybridoma, B151K12, as well as recombinant TRF/IL-5 (rec-TRF) were used for the analysis. Maximum anti-2,4-dinitrophenyl (DNP) IgG antibody response of DNP-primed B-cells or polyclonal IgM secretion of B-cell tumor line BCL1 was seen when HPLC-purified B151-TRF was added or when suboptimal doses of B151-TRF were added to the culture in the presence of IL-2. Normal resting B-cells gave maximum anti-SRBC IgM PFC responses when HPLC-purified B151-TRF and IL-2 were present. The purified B151-TRF as well as rec-TRF also induced on B-cells increased expression of IL-2 receptors that react with monoclonal anti-murine IL-2 receptor antibody, PC61, and 125I-labelled IL-2. The numbers of functional high affinity IL-2 receptors on activated B cells increased at least 20-fold by culturing them with purified B151-TRF. Moreover, B151-TRF induced increase in the levels of steady-state mRNA for IL-2 receptor by approximately 8-fold. These results suggest that activated B-cells as well as BCL1-cells may express functional IL-2 receptors or closely related molecules when stimulated with HPLC-purified B151-TRF as well as rec-TRF.

Interferon-gamma and B cell stimulatory factor-1 reciprocally regulate Ig isotype production

Gamma interferon (IFN-gamma) and B cell stimulatory factor-1 (BSF-1), also known as interleukin-4, are T cell-derived lymphokines that have potent effects on B cell proliferation and differentiation. They are often secreted by distinct T cell clones. It is now shown that IFN-gamma stimulates the expression of immunoglobulin (Ig) of the IgG2a isotype and inhibits the production of IgG3, IgG1, IgG2b, and IgE. By contrast, BSF-1 has powerful effects in promoting switching to the expression of IgG1 and IgE but markedly inhibits IgM, IgG3, IgG2a, and IgG2b. These results indicate that BSF-1 and IFN-gamma as well as the T cells that produce them may act as reciprocal regulatory agents in the determination of Ig isotype responses. The effects of IFN-gamma and BSF-1 on isotype expression are independent.

Preexposure of resting B cells to interferon-gamma enhances their proliferative response to subsequent activation signals

In this report we demonstrate that pretreatment of resting splenic B cells with IFN-gamma increases their mitogenic response to subsequent activating stimuli. This effect is completely blocked by neutralizing anti-IFN-gamma antibodies. By contrast, a similar effect induced by partially purified BCGF is not completely inhibited by anti-IFN-gamma antibody, inferring that as in the mouse, a B-cell-specific factor may also induce increased responsiveness to mitogens in resting B cells. The mechanism of this response was analyzed. Phenotypic and cell cycle analyses of the IFN-gamma-treated cells following activation were not significantly different from control cells with respect to kinetics, although as expected from thymidine uptake, more cells were actively cycling. Even when a very early manifestation of cell activation, Ca2+ flux was examined, no response to IFN-gamma alone was evoked, and the response to subsequent activation was identical to that of control cells. These data show that IFN-gamma did not directly activate B cells, but primed B cells in a manner which amplified subsequent mitogenesis.

Bovine interferon: its biology and application in veterinary medicine

Investigations of the production and potential use of bovine interferons against viral infections have occurred since the first descriptions of interferons in other systems. The recent advent of recombinant DNA-technology has facilitated such studies and furthered our knowledge about the bovine interferon system in general. This review gives an overview of the biology, antiviral and immunomodulatory activities of bovine interferons. Areas in which the interferons are now applied or have potential application in viral diseases in cattle are described. Finally, the value of studies of the bovine interferon system with respect to comparative interferon research is discussed.

The role of gamma interferon in B-cell activation

This study evaluates the role of gamma interferon in in vitro B-cell activation. Two clones of an alloreactive helper T-cell line were equally effective in activating B cells polyclonally to proliferate and to mature to immunoglobulin secretion. One of these clones produced high levels of gamma interferon, while the other clone did not. From these data we conclude that gamma interferon plays no limiting role in T-dependent B-cell activation.

Induction of murine gamma interferon production by lipopolysaccharide and interleukin-2 in Propionibacterium acnes-induced peritoneal exudate cells

Lipopolysaccharide (LPS) induces high levels of gamma interferon (IFN-gamma) in the circulation of mice pretreated with heat-killed Propionibacterium acnes. The following results were obtained in the present study. LPS, as well as interleukin-2 (IL-2), was also able to induce IFN-gamma in vitro in peritoneal exudate cells (PEC) from such mice. Splenocytes and lymph node cells from these mice or resident peritoneal cells from control mice produced trace or undetectable amount of IFN-gamma upon exposure to LPS. A synergistic effect on IFN-gamma induction was observed when LPS was added to a culture of PEC together with IL-2. Indomethacin augmented the induction of IFN-gamma by LPS or IL-2, and prostaglandin E2 reversed its effect. Deprivation of plastic-adherent or nylon wool-adherent cells abolished the induction by LPS or IL-2, whereas it did not affect that by concanavalin A. Culture supernatant of plastic-adherent cells incubated with LPS stimulated the nylon wool-nonadherent cells to produce IFN-gamma in the presence of IL-2, but interleukin-1 or phorbol myristic acetate did not replace the LPS-stimulated supernatant. The ability of PEC to produce IFN-gamma measured as a function of time after P. acnes injection increased in proportion to their natural killer (NK)-like activity against YAC-1 cells. Moreover, treatment of PEC with monoclonal anti-Thy-1 antibody or with anti-asialo GM1 antiserum plus complement eliminated the production of IFN-gamma and the NK-like activity simultaneously, whereas treatment with monoclonal anti-Lyt-2 antibody plus complement did not. These results suggest that IL-2 and some unidentified factor released from plastic-adherent cells by LPS stimulation cooperatively induce IFN-gamma production in activated, Thy-1- and asialo GM1-positive NK-like cells appearing in inflammatory reactions and that prostaglandin E2 regulates IFN-gamma production in these cells.

Neither interleukin 2 nor gamma interferon directly promote growth or differentiation of mouse B cells

The roles of interleukin 2 (IL-2) and gamma interferon (IFN-gamma) as direct mediators of B-cell growth and differentiation were analysed. Products of cloned genes were used in both cases. The use of flow cytometric assays coupled with density fractionation of responding splenic B-cell populations enabled both the characterization of B cells responding to various stimuli and the estimation of their frequency. B cells responding to non-IL-2 related lymphokines promoting growth and differentiation were restricted to low buoyant density fractions. In addition, these cells expressed densities of IL-2 receptor determinants comparable to those found on T cells, although, IL-2 did not support their growth or differentiation. The inability to demonstrate any direct effect of either IL-2 or IFN-gamma on B cells in any state of activation suggests that their physiological roles are mediated through additional cell types.