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At least 19 recordsLinked to original sources
PubMed1986

Antibody-induced antigenic modulation is antigen dependent: characterization of 22 proteins on a malignant human B cell line.

Expression of several of the surface antigens on normal and malignant hematopoietic cells is reduced or is modulated by incubation with specific antibodies. Although antigenic modulation provides a means by which cells can escape antibody-mediated immune destruction, the physiologic significance and frequency of this phenomenon are both poorly understood. To begin to address these issues, we identified and characterized surface antigens on the malignant B cell line Laz 221 established from a patient with acute lymphoblastic leukemia (ALL). Indirect immunofluorescence analysis with the use of 26 hematopoietic cell populations and immune precipitation studies with the use of iodinated ALL cells indicate that 163 monoclonal antibodies (MoAb) identify 22 different proteins on this cell line, including at least six previously described surface molecules. Seven of these antigens are expressed by all nucleated cells examined, whereas only the mu chain of immunoglobulin is B cell specific. Incubation of specific MoAb with cultures of Laz 221 cells at 37 degrees C reduces or modulates surface expression of five of these 22 antigens (p45, immunoglobulin mu chain, transferrin receptor, common ALL antigen (CD10), and p105). Studies that made use of multiple MoAb specific for the same antigen suggest that the capacity for antigenic modulation is an intrinsic property of individual antigens. These studies also suggest that the murine immune response to shared human antigens varies from one immunizing cell population to another. For example, three of the antigens present on Laz 221 cells were only identified by MoAb raised to the Burkitt's cell line Ramos and vice-versa. Only one of these six shared antigens is present in greater amounts on the immunogenic cell population. Immunogenicity of individual human antigens in the mouse may be a function of their cell surface environment.

Antibodies, Monoclonal↗
PubMed1992

Antibodies to varicella-zoster virus modulate antigen distribution but fail to induce viral persistence in vitro.

Varicella-zoster virus (VZV) persists in human sensory ganglia. One of the hypotheses to explain the induction or the maintenance of VZV latency is that it could be promoted by the immune response itself. It is known that in the case of viruses which bud off the infected cell membrane, virus-specific antibodies can induce antigenic modulation, i.e., spatial redistribution of viral antigens and modulation of their synthesis. To determine whether antigenic modulation occurs during VZV infection in vitro and could possibly be involved in viral persistence, we have grown infected cells in the presence of anti-VZV antibodies either transiently or permanently. The distribution of immune complexes and viral proteins was then analyzed. In transient immunomodulation experiments, the distribution of one or more viral antigens was modified not only in the cytoplasmic membranes but also in the cytoplasm and nucleoplasm of infected cells. When infected cells were kept permanently in the presence of antibodies, the same pattern of redistribution of immune complexes was observed and the localization of internal viral glycoproteins was significantly modified. However, antibodies did not prevent the lytic effect of infection; they altered neither the infectious virus yield nor the Western immunoblot pattern of viral proteins, suggesting that immunomodulation is not the primary effector of viral persistence.

Antibodies, Viral↗
PubMed1992

Identification of anti-CD3 antibodies that do not modulate antigen but induce mitogenesis and block the mixed lymphocyte reaction.

Using a panel of anti-CD3-TCR monoclonal antibodies (OKT3 A-E), it appears possible to separate the ability to cause surface antigen modulation from inhibition of MLR or induction of mitosis. OKT3D, an antibody that recognizes the CD3 antigen at a site that can be differentiated from the epitopes recognized by other members of this panel by competition binding, does not cause antigen modulation when incubated with human T cells for up to 3 days. Despite this, OKT3D is mitogenic and is capable of blocking MLR. Two different isotypes were produced from the OKT3D clone, IgG1 and IgG2b. The IgG2b isotype of OKT3D blocked MLR even in individuals unable to respond mitogenically to this antibody. Use of members of this panel may now permit dissection of the types of signals delivered by the CD3-TCR complex inducing mitosis, receptor modulation, and other T-cell responses.

Animals↗
PubMed1979

Antigenic modulation in vitro. III. Failure to modulate H-2 antigens on several mouse tumors.

The capacity of various malignant and normal mouse cells to acquire resistance to lysis by guinea pig complement during exposure to H-2 antisera in vitro at 37 degrees C (antigenic modulation) was examined. All tumors tested, including cell lines of the TL+ leukemias RADA1, ASL1, and RLmale1, the TL- leukemia EL 4, myelomas MOPC-70A and S194, and the sarcoma Meth A, failed to modulate when incubated with multispecific or monospecific H-2 antisera up to 24 hours, even though under comparable conditions thymus-leukemia (TL) antigens and surface IgG molecules modulated within several hours. Indirect sensitization of RADA1 leukemia cells with H-2 antisera followed by antiserum against mouse IgG also failed to induce H-2 antigen modulation. Normal peritoneal cells from certain mouse strains were partially modulated with H-2D-specific or H-2K-specific and monospecific antisera within several hours, but normal thymus and lymph node cells did not modulate. Modulation of peritoneal cells occurred without a complete loss of sensitizing H-2 antibody from the cell surface and required a cobra venom factor-sensitive activity that could be restored by human complement component C3. Modulation of TL antigens in vitro had previously been shown to have similar characteristics.

Animals↗
PubMed1968

Antigenic modulation. Loss of TL antigen from cells exposed to TL antibody. Study of the phenomenon in vitro.

Antigenic modulation (the loss of TL antigens from TL+ cells exposed to TL antibody in the absence of lytic complement) has been demonstrated in vitro. An ascites leukemia, phenotype TL.1,2,3, which modulates rapidly and completely when incubated with TL antiserum in vitro, was selected for further study of the phenomenon. Over a wide range of TL antibody concentrations modulation at 37 degrees C was detectable within 10 min and was complete within approximately 1 hr. The cells were initially sensitized to C' by their contact with antibody, thereafter losing this sensitivity to C' lysis together with their sensitivity to TL antibody and C' in the cytotoxic test. The capacity of the cells to undergo modulation was abolished by actinomycin D and by iodoacetamide, and by reducing the temperature of incubation to 0 degrees C. Thus modulation apparently is an active cellular process. Antigens TL. 1,2, and 3 are all modulated by anti-TL.1,3 serum and by anti-TL.3 serum. This modulation affects all three TL components together, even when antibody to one or two of them is lacking. aAnti-TL.2 serum does not induce modulation and in fact impairs modulation by the other TL antibodies. The influence of the TL phenotype of cells upon the demonstrable content of H-2 (D region) isoantigen, first shown in cells modulated in vivo, has been observed with cells modulated in vitro. Cells undergoing modulation show a progressive increase in H-2 (D region) antigen over a period of 4 hr, with no change in H-2 antigens of the K region. Restoration of the TL+ phenotype of modulated cells after removal of antibody is less rapid than TL+ --> TL- modulation and may require several cell divisions.

Amides↗
PubMed1985

Role of the main immunogenic region of acetylcholine receptor in myasthenia gravis. An Fab monoclonal antibody protects against antigenic modulation by human sera.

Antigenic modulation of acetylcholine receptor (AChR), i.e., acceleration of its internalization and degradation rate by antibody-cross-linking, is considered to be one of the two main causes of AChR loss in myasthenia gravis (MG). The majority of the antibodies to AChR are directed to the main immunogenic region (MIR) on the alpha-subunit of the receptor. We here examine the relative contribution of the anti-MIR antibody fraction (as well as of another fraction) to the antigenic modulation caused by MG patients' sera. Fab fragments of an anti-MIR monoclonal antibody (mAb) or a mAb to the beta-subunit (neither of which causes antigenic modulation) were allowed to shield their corresponding regions on the AChR on the mouse muscle cell line BC3H1. The 27 MG sera subsequently added thus bound to all other regions except to the protected one, and the resulting antigenic modulation was measured. The anti-MIR mAb protected the AChR by 68 +/- 16%. This is interpreted as the contribution to antigenic modulation of the anti-MIR antibody fraction in the human sera. This percentage correlated very well with the occurrence of the anti-MIR antibodies in the same sera. The anti-beta mAb gave only small protection of the AChR. No significant pattern differences were observed between sexes, early and recent onset of the disease, or high and low antibody titers. It is concluded that as far as it concerns the one of the pathogenic mechanisms in MG, i.e., the antigenic modulation, the MIR seems to be the main pathogenic region. The observation that a single mAb can efficiently protect the AChR in this system may prove to be of therapeutic interest.

Animals↗
PubMed1992

Passive transfer of experimental myasthenia gravis via antigenic modulation of acetylcholine receptor.

Antigenic modulation of acetylcholine receptor (AChR) is considered to contribute to the reduction of endplate AChR in myasthenia gravis (MG). Yet, the pathogenic significance of this mechanism is unclear. To investigate the in vivo role of AChR antigenic modulation we examined the ability of bivalent F(ab')2 and monovalent Fab fragments of monoclonal antibody (mAb) 35 to passively transfer experimental autoimmune MG (EAMG) in rats. mAb 35 which binds at the main immunogenic region (MIR) of the AChR causes severe EAMG without being involved in channel function. Compared to the intact mAb, F(ab')2 35 proved to be less potent but still capable of inducing moderate EAMG, whereas Fab 35 were totally ineffective. Furthermore, both intact and F(ab')2 35 induced mild EAMG in complement-depleted rats. These results (a) provide evidence that antigenic modulation of endplate AChR is sufficient to generate passive transfer of EAMG and (b) further support the pathogenic potential of the anti-MIR antibodies in MG.

Animals↗
PubMed1982

Antibody affinity may influence antigenic modulation of the common acute lymphoblastic leukemia antigen in vitro.

We have produced a new monoclonal antibody designated BA-3. An extensive side-by-side serologic comparison of BA-3 with the anti-common acute lymphoblastic leukemia antigen (CALLA) monoclonal antibody J-5 was undertaken. Cells examined included established leukemic cell lines, malignant cells from patients with newly diagnosed leukemia/lymphoma, and normal hematopoietic tissues. In all experiments the cellular distribution of the antigens recognized by BA-3 and J-5 were identical when analyzed by immunofluorescent microscopy and the FACS. Iodination of NALM-6 cells, followed by radioimmunoprecipitation and SDS-PAGE, indicated that BA-3 (like J-5) precipitated a glycoprotein of approximately 100,000 daltons. Competitive binding studies using 125I-labeled BA-3 indicated that BA-3 and J-5 were binding to closely associated (if not identical) epitopes on CALLA. Calculation of the equilibrium constant (K value) for BA-3 and J-5, and the approximate number of CALLA molecules per cell, was graphically determined using Scatchard plots. BA-3 and J-5 were shown to have K values of approximately 2.7 x 10(7) M-1 and 7.2 x 10(7) M-1, respectively, with NALM-6 cells expressing 1 x 10(5) to 2 x 10(5) CALLA molecules per cell. Additional studies with BA-3 failed to demonstrate significant antigenic modulation of CALLA in vitro using fresh leukemic cells and leukemic cell lines. Thus, we suggest that antibody affinity may be a significant factor influencing antigenic modulation of CALLA in vitro.

Antibodies, Monoclonal↗
PubMed1974

Antigenic modulation in vitro. I. Fate of thymus-leukemia (TL) antigen-antibody complexes following modulation of TL antigenicity from the surfaces of mouse leukemia cells and thymocytes.

The modulation or loss of thymus-leukemia (TL) antigenicity from the surfaces of mouse RADA1 leukemia cells and normal thymocytes during incubation with TL antibody in vitro at 37 degrees C was investigated by cytotoxicity, immunofluorescence, and immunoelectron microscopy. The fate of bivalent and monovalent antibody during modulation was visualized by fluorescence microscopy. Considerable antibody remained bound to the cell surface after modulation, bivalent antibody being displaced topographically into "patches" and "caps" while monovalent antibody was only slightly aggregated on the cell surface. Some antibody was internalized, presumably by pinocytosis, and was sequestered into the Golgi region of the cell. Capping usually occurred over the pole of the cell opposite from the Golgi region, which may explain the lack of extensive pinocytosis of modulating bivalent antibody. Since modulation with monovalent antibody occurs without patch or cap formation, gross topographical redistribution of TL antigen-antibody complexes is not required for modulation, although more subtle displacement of these complexes may be involved. Modulation was demonstrable by cytotoxicity with guinea pig C' but not with absorbed rabbit C', indicating that modulated TL antigens remain bound to the cell surface. A heat-labile factor in TL antiserum and in mouse serum in general is responsible for "blocking" the cytolytic interaction of guinea pig C' with modulated TL antigen-antibody complexes.

Animals↗
PubMed1984

T65 antigen modulation in a phase I monoclonal antibody trial with chronic lymphocytic leukemia patients.

Antigenic modulation of the T65 cell surface antigen was assessed in chronic lymphocytic leukemia patients (CLL) receiving therapy with the murine monoclonal antibody T101 in a phase I clinical trial. A total of 12 patients received 1, 10, or 40 mg doses administered over 2 hr, or 50 or 100 mg doses administered over 50 hr. Decreases in T65 antigen expression (up to 90%) coincided with decreases in the circulating leukemic cell count in those patients who received T101 over a 2-hr period, indicating that clearance of circulating T65 antigen-positive cells could account for most of the observed decreases in T65 antigen expression. In contrast, analysis of bone marrow specimens from these patients indicated that decreases in T65 antigen density in this relatively stationary population resulted not from a cell decrement but rather from antigenic modulation. Pulmonary toxicity prevented administration of doses greater than 40 mg over a 2-hr period; therefore, higher doses (50 and 100 mg) were administered over a 50-hr period. This treatment schedule resulted in greater than 90% reduction in T65 antigen density of both circulating and bone marrow leukemic cells without dramatic drops in circulating leukemic cell counts, indicating that antigenic modulation accounted for most of the observed decreases in T65 antigen density under these conditions. Reexpression of T65 antigen by modulated cells was observed both in vitro and in vivo within 2 to 4 days. Immunoperoxidase staining of in vivo-modulated specimens and in vitro modulation studies with 125I-T101 suggested that T65 antigen-T101 antibody complexes were internalized during modulation. Although antigenic modulation inhibits the potential therapeutic effectiveness of unconjugated T101 antibody in CLL patients, treatment of CLL with T101 drug or toxin immunoconjugates under conditions that bring about rapid and extensive internalization of the T65 antigen may provide an effective means of therapy.

Antibodies, Monoclonal↗
PubMed1977

Antigenic modulation of Friend virus erythroleukemic cells in vitro by serum from mice with dormant erythroleukemia.

Friend leukemia virus (FLV) erythroleukemic cells cultured in medium containing FLV-immune serum from dormant FLV-infected mice undergo modulation of FLV cell surface antigens. Modulation was determined by an increased resistance to FLV antibody-mediated complement-dependent lysis and was associated temporally with the capping of FLV-immune complexes at the cell surface. Modulated cells regained their susceptibility to FLV antibody-mediated complement-dependent lysis when transferred to medium containing normal mouse serum. After 48 h of culture in FLV-immune serum, 26% of the FLV erythroleukemic cells were devoid of FLV cell surface antigens as demonstrated by immunofluoresence. Antigenic modulation occurred to a greater extent in cells maintained in logarithmic growth than in cells in GO or resting phase. FLV-antigenic modulation is discussed as a possible mechanism by which antibody induces and maintains FLV-transformed cells in a dormant state.

Animals↗
PubMed1980

Antigenic modulation of mammary tumour virus envelope antigen or GR thymic lymphoma cells in relation to expressions of H-2, TL cell-surface antigens and THY1.

The MLr antigen, a mammary tumour virus-induced antigen on the surface of GR thymic lymphoma cells (GRSL) can be modulated from the cell surface upon incubation with specific antiserum for 1-2 h at 37 degrees C, followed by washing the cells. In contrast, a number of other cell-surface antigens on these GRSL cells cannot be modulated under similar conditions. These antigens include histocompatibility antigens of the H-2 complex (H-2.8 of the K-end and H-2dx(D) of the H-2dx haplotype) and two thymic markers, TL1.2 and Thy1.2. Antigenic modulation of MLr as tested by trypan-blue exclusion and by chromium51 release does not lead to a measurable change in the expression of H-2K, H-2D, TL and Thy1.2 antigens. These results could be confirmed by absorption analysis. The latter analysis showed that the number of antigenic sites per cell are about the same for MLr and the two H-2 antigens, while TL antigens are scarcer and Thy1.2 antigens are more abundant. The procedure of antigenic modulation showed that the MLr antigen resides on MTVgp52, the major protein of the envelope. There was no evidence of internal proteins, such as MTVp27, on the surface of GRSL cells.

Animals↗
PubMed1979

Susceptibility of Friend virus antigen-modulated erythroleukemic cells to lysis by T lymphocytes from mice with dormant Friend virus infections.

Spleen cells from DBA/2 mice with dormant Friend leukemia virus (FLV) infections or from mice immunized with x-irradiated FLC-745 erythroleukemic cells are not cytolytic for FLC-745 cells when tested directly, but acquire cytolytic activity in vitro by cultivation with x-irradiated FLC-745 cells. Spleen cells cultured from normal mice do not acquire such cytolytic activity. Cytolytic activity resides in the T lymphocyte population. Alloantiserum, but not antisera against FLV-virion polypeptides, inhibited the lysis of FLC-745 cells by cytolytic T lymphocytes. To understand further the role of cellular and humoral immune anti-FLV responses in mice with dormant FLV-infections, in vitro experiments were conducted that mimicked the in vivo FLV-specific immune environment of these mice. We found that FLV-immune serum from mice with dormant FLV-infections modulated FLV-antigen expression on the surfaces of FLC-745 cells without affecting their susceptibility to lysis by cytolytic T lymphocytes. These results suggest that cytolytic T lymphocyte restrain the outgrowth of FLV-antigen-modulated erythroleukemic cells in mice with dormant FLV infections and that the targets for cell-mediated lysis may be H-2d-associated antigens.

Animals↗
PubMed1988

Inhibition, by vinca alkaloids and colchicine, of antigenic modulation induced by anti-CD19 monoclonal antibodies.

Several clinical trials have been reported in which monoclonal antibodies (McAb) were used for therapy of lymphoid malignancies. Such trials have shown that infusion of McAb recognizing lymphoid antigens, is well-tolerated, and leads to the coating of tumor cells and tumor regression in some patients. However, the tumoricidal capacity of a McAb is hampered by the presence of circulating free antigen, antigenic modulation, development of human anti-mouse antibodies, emergence of antigen-negative variants of tumor cells and the inadequacy of host-effector cell mechanisms. We have studied the antigenic modulation induced by immunoglobulin (Ig) heavy chain switch variants of anti-CD19 McAb. Modulation of CD19 molecules was not related to the IgG subclass of the McAb. Immunofluorescence studies on the Burkitt tumor cell line Daudi showed that CD19 molecules are internalized after incubation by anti-CD19 McAb. Next, the effect of cytoskeleton inhibitors on antigenic modulation was studied. We found that antigenic modulation on Daudi cells and on an Epstein-Barr virus-transformed B-cell line was completely inhibited by vinca alkaloids (VA) or by colchicine. Interestingly, antigenic modulation of tumor cells from a VA-resistant patient, was not inhibited by VA or colchicine. These findings provide information for the rational design of more effective clinical trials with McAb.

Antibodies, Monoclonal↗
PubMed1986

Antigenic modulation of human myotube acetylcholine receptor by myasthenic sera. Serum titer determines receptor internalization rate.

Antibodies to the acetylcholine receptor (AChR) added to AChR-bearing muscle cells cross-link the receptors, thus increasing their internalization and degradation rate (antigenic modulation). This mechanism contributes to AChR loss in myasthenia gravis. Until recently, antigenic modulation has been studied in animal tissues, where only a small fraction of human anti-AChR antibodies bind. In the present study, we examined the antigenic modulation of AChR by using patients' sera and cultures of human muscle cells. We aimed to see whether antigenic modulation correlates better with disease severity or with antibody titer. Antibody-containing sera from 29 myasthenic patients in various states of the disease and with different antibody titers against AChR were tested. Control sera from six healthy individuals were also tested. Our experiments showed that all myasthenic sera affected the overall AChR content on the human myotube surface, causing a 49 to 82% loss, whereas control sera had no effect. Although at fixed serum volumes there was some correlation between disease severity and AChR loss, this effect was clearly due to differences in antibody titers. In fact, the antigenic modulation depended mainly on the final concentration of the antibody present. Thus, intrinsic factors other than antibodies to AChR may determine or influence the patients' susceptibility to the disease.

Antigens↗
PubMed1989

Fab fragments of monoclonal antibodies protect the human acetylcholine receptor against antigenic modulation caused by myasthenic sera.

The human cell line TE671 produces large amounts of muscle nicotinic acetylcholine receptor (AChR). TE671 cells were used to determine the specificity of antibodies which can increase the internalization rate of AChR (antigenic modulation) and to test procedures for protecting AChR against this mechanism. The half-life of AChR both in the absence and the presence of anti-AChR antibodies was very similar to that of AChR on human muscle cell cultures. The relative contribution of different anti-AChR antibody fractions to the total antigenic modulation capacity of human myasthenic sera was investigated by competition experiments between Fab fragments of anti-AChR monoclonal antibodies (MoAbs) and intact antibodies (MoAb or myasthenic sera). Fab fragments, which do not induce antigenic modulation, were allowed to shield the corresponding regions of the AChR. Intact antibodies were subsequently added. It was found that protection of the main immunogenic region (MIR), but not of a region on the beta-subunit, essentially blocked the modulatory effect of the intact anti-MIR MoAbs, and approximately 80% of that of myasthenic sera. These data suggest that anti-MIR antibodies are mainly responsible for the loss of human AChR via antigenic modulation. Furthermore the observation that Fab fragments of anti-MIR MoAbs can efficiently protect AChR against antigenic modulation may have therapeutic implications.

Animals↗
PubMed1990

The OKT3 immunosuppressive effect. In situ antigenic modulation of human graft-infiltrating T cells.

OKT3 exerts its in vivo immunosuppressive effects by inducing major peripheral T cell depletion as well as antigenic modulation of the T3/Ti T cell receptor complex. Modulated cells, which reversibly lose the expression of the CD3 T cell receptor molecular complex but still share the CD4 and CD8 antigens, have been shown to be functionally immunoincompetent. Antigenic modulation is maintained as long as significant OKT3 serum levels are present. Cells infiltrating renal allografts from seven OKT3 treated patients were studied by double immunofluorescence to assess whether antigenic modulation could affect cells located in profound organs such as renal allografts. Needle biopsies were obtained in patients given OKT3 (5 mg/day) for at least 10 consecutive days in association with conventional immunosuppressive drugs for treatment of a rejection episode (5 cases) or prophylactically (2 cases). In all patients at the time of biopsy, CD3 positive cells were absent from the circulation, significant OKT3 serum levels were present, and neither IgG nor IgM anti-OKT3 antibodies were detected. Infiltrating cells were double-labeled using a combination of either anti-CD3 and anti-CD4 or anti-CD3 and anti-CD8 monoclonal antibodies. Following 7-14 consecutive days of treatment, all patients given OKT3 for a rejection episode showed a significant decrease in the number of graft-infiltrating lymphocytes. Importantly, all T cells still infiltrating the allograft were CD3-CD4+ or CD3-CD8+ cells, which is exactly the same phenotypical pattern of CD3 circulating modulated T cells. In 6 out of the 7 patients, this phenotypical pattern was associated with clinically normal graft function. These results further underline the fact that antigenic modulation is an important mechanism mediating the immunosuppressive effect of OKT3 both in peripheral blood and in renal allografts.

Antibodies, Monoclonal↗