Hepatotoxic effects of SH-reagents in human and rat hepatocyte cultures and in situ perfused rat livers

Effects organic mercurials (PCMBS, PCMB, mersalyl) an alkylating reagent (NEM), disulphide reagents (DTP, CPDS) and the dithiocarbamate agent DSF (disulfiram) were studied in hepatocyte culture. Cytotoxicity, was on a high level (organic mercurials), moderate (NEM, DTP), or none (DSF, CPDS). The organic mercurials and NEM induced glutathione depletion. Disulphide compounds were detoxified by metallothionein binding. Organic mercurials inhibited the cellular glucose uptake. The most prominent effect of NEM, DTP and DSF was an inhibition of the TCA-cycle. The hepatocellular BSP metabolism was delayed by all tested compounds. Albumin synthesis was stimulated by pyruvate and blocked by PCMB and PCMBS, by inhibiting the hepatocellular amino acid uptake. Phase I and II biotransformation reactions were inhibited by PCMBS and PCMB by direct binding to Cyt. P450 cysteinyl-residues and active sites of UDP-glucuronyltransferases. DSF probably reacts by diminishing the availability of the cofactor NADPH. Isolated ALDH (EC 1, 2, 1.3) was inhibited by all studied compounds. In cellular systems, DSF and the organomercurials inhibited ALDH, thereby reducing the cell's capacity of ethanol catabolism. All tested compounds showed, in low doses, the anabolic ability of insulin mimicking, as demonstrated in a balanced endocrine in vitro testsystem. Morphology, Exposure to NEM, DTP, CPDS, DSF did not result in any morphological alterations in the cell cultures. However, an exposure to PCMBS and PCMB, resulted in extensive bleb-formation, as a result of SH group blocking at the cell's outer membrane. It can be concluded, that cultured hepatocytes from human or rat origin, resist an exposure to alkylating and disulphide SH-reagents up to relatively high dose (1.0 mM). However, organic mercury compounds triggered an extensive bleb formation, as a result of SH-blocking, thereby disturbing the osmotic balance by blocking Na+/K+ carriers. Of all tested reagents, organic mercury compounds arose as the most toxic reagents.

Photodynamic effects of protoporphyrin on the cellular level-an in vitro approach

The purpose of this study was characterizing the phototoxic action of protoporphyrin and cellular protection mechanisms, as studied on the cellular level. In this process, active oxygen is involved. As a biological system, rat hepatocyte short-term and primary cultures were used. Phototoxicity of protoporphyrin could be observed, after previous absorption of protoporphyrin to membrane structures. Damaging of several cell organelles occurred, such as mitochondria and lysosomes. Peroxisomes were not affected. Coated vesicles located at the periphery of the cells' interior suggested that protoporphyrin absorption is mediated by an active uptake (endocytosis), as well as passive diffusion. Lipid peroxidation played a role in protoporphyrin phototoxicity. Cellular protection mechanisms such as superoxide dismutase and the scavenger glutathione (GSH) protected the cells from active oxygen toxicity. In conclusion, protoporphyrin entered the cells by diffusion and endocytosis. Previous adsorption to the membrane structures was necessary for the expression of protoporphyrin phototoxicity. However, active oxygen itself could not be demonstrated. Lipid peroxidation was involved in cell-damaging processes. Mechanisms of protoporphyrin phototoxicity on the cellular level were studied. Rat hepatocyte primary and short-term cultures proved to be suitable in vitro systems for studying biochemical and morphological effects on the cellular level.

The use of the divalent calcium-ionophore A23187 as a biochemical tool in pharmacological and in vitro toxicological studies

The use of A23187 as a biochemical tool is described. A23187 was used to elucidate the mechanisms of intracellular transport and secretion of N-hydroxylated aniline metabolites in rat hepatocyte primary culture. Results indicate a membrane-bound intracellular transport. Also, A23187 induced macrophages in their anti-tumour cytostatic activity using P815 tumour cells in in vitro co-cultures of macrophages and tumour cells. Results indicate the activating role of A23187 in macrophage leukotriene C4 release and enhanced macrophage anti-tumour activity. In conclusion, A23187 proved to be a useful tool in studying calcium dependent metabolic processes.

Effects of sulphydryl reagents on receptor-mediated hormonal responses at the cellular level: insulin-mimicking characteristics of thiol-blocking compounds in rat hepatocyte primary cultures

The interference of various SH-blocking chemicals with the insulin-controlled regulation of the hepatic carbohydrate metabolism was studied in rat hepatocyte primary cultures. The organic mercurials PCMB, PCMBS, mersalyl the disulphide agents DTP, CPDS, disulfiram and the SH-alkylating reagent NEM were used as experimental SH-blocking model compounds. All studied compounds, except for NEM, induced an increased glycogen deposition comparable with the physiological insulin-induced glycogen-deposition. PCMBS appeared to be the most effective insulin-mimicking anabolic trigger. The action of the insulin molecule itself was potentiated by PCMBS as well as demonstrated by increased glycogen deposition, induced pyruvate kinase (PK) and decreased phosphoenol-pyruvate carboxykinase (PEP-CK) activity. However, cell-exposure to insulin and PCMBS in relatively high doses was destructive, as demonstrated by decreased glycogen levels, most probably as a result of insulin-receptor overstimulation and metabolic stress. Thus, SH-blocking compounds are able to trigger insulin-dependent metabolic processes. The relatively non-permeant organic mercurial PCMBS proved to be the most effective insulin-mimicking SH-blocking compound.

Pseudotumour cerebri as a side effect of leuprorelin acetate

Leuprorelin acetate is a synthetic nona-peptide analogue of the naturally occurring gonadotrophin releasing hormone LH-RH (hypothalamus), used in the treatment of sterility, endometriosis or prostatic cancer. In a 35 year old woman, treated with leuprorelin acetate, after 5 months treatment, the side-effects (hot flushes, sweating, sleeping disorders), appeared to be rather unbearable. Medication was ended. The endocrine reversion to the normal physiological balance was association with high fever (38.9 degrees C) during an 8 day period. Increasing scotomas resulted in a gradual loss of eyesight in one eye, associated with a normal visual acuity. Unilateral papilloedema was observed, indicating the possibility of tumor cerebri. Fluorescein angiography demonstrated an intense leakage of the right optic disc. No signs of retinal vascular malformations were seen. The eye pressure was normal. No signs of hemorrhages were observed. Visual field examination showed an enlarged blind spot with a few scotomas above the centre of fixation. CT scan of the brain was normal, the cerebrospinal fluid (CSF) was normal, indicated by IgG production. Six months after ending the leuprorelin acetate treatment, the eyesight was spontaneously 100% recovered. It is most likely that leuprorelin acetate is responsible for the emergence of pseudotumor cerebri. As described by Prof. Sidi et al(1), leuprorelin strongly induces increased liquor pressure, being the intermediate mechanism between hormonal treatment and an ante grade mechanical force, on the optic nervus. Because of the risk of permanent loss of eyesight, it is strongly advised to verify eye parameters conscientiously during leuprorelin treatment.

Effects of SH-blocking compounds on the energy metabolism in isolated rat hepatocytes

To investigate the importance of SH-groups in the energy metabolism of liver cells, isolated rat hepatocytes were exposed to various SH-blocking compounds. After 1.0 hr exposure, the cells were analyzed for the content of glycogen, lactate, pyruvate, ATP and the rate of oxygen consumption. Without affecting the cell viability, PCMB, PCMBS, mersalyl, NEM, DTP and DSF were found to decrease glycogen levels, whereas the disulphide reagent CDPS did not affect this endogenous energy reserve. Lactate and pyruvate levels were decreased by the organic mercury compounds, whereas NEM, DTP and DSF stimulated the formation of lactate, without affecting the levels of pyruvate. In both situations the oxygen consumption was slightly decreased. The FCCP uncoupled oxygen consumption was not affected. Up to the point of loss of cell viability, as measured by trypan blue exclusion and LDH-leakage, the liver cells maintained their ATP levels, during exposure to the various SH-reagents. In conclusion, the results with organic mercury compounds suggest a reaction of these agents with SH-groups in the outer membrane of cells, having an inhibiting effect on the glucose uptake. The most prominent effect of DTP, DSF and NEM was an increased lactate formation, implying an intracellular effect, most probably in the TCA-cycle.

Binding of the human complement subcomponent C1q to hybrid mouse monoclonal antibodies

Activation of the classical pathway of the complement system is initiated by the binding of C1q to antibody complexes. Here we evaluated the C1q binding capacity of series of monospecific and bispecific hybrid mouse monoclonal antibodies (mAb) and compared them with parental (conventional) mAb. The hierarchy in C1q binding capacity of the bispecific anti-HuIgA1/HRP mAb with homologous H-H chain combinations (IgG2a-2a, IgG2b-2b and IgG1-1) and the parental anti-HuIgA1 or anti-HRP mAb was identical; IgG2a greater than IgG2b much greater than IgG1. Hybrid IgG1-2a mAb bind intermediate amounts of C1q when compared with the IgG1 and IgG2a parental antibodies. IgG1-2b and IgG1-1 hybrid mAb did not bind any C1q, like the IgG1 mAb. We could not observe any difference in C1q binding efficiency between monovalently bound IgG1-2a, IgG2a-2a and IgG2b-2b anti-HuIgA1 HRP mAb and the bivalently bound IgG1-2a, IgG2a-2a and IgG2b-2b anti-HuIgA1 mAb, respectively. Furthermore, these hybrid ms anti-HuIgA1 and bs anti-HRP/HuIgA1 mAb were able to lyse HuIgA1-coated erythrocytes, in the presence of 50% human serum, as efficiently as their parental counterparts. These data indicate that a simultaneous binding of both F(ab') fragment to antigen is not a necessary prerequisite for binding and activation of C1q.

RT7-defined alloantigens in rats are part of the leucocyte common antigen family

Haemopoietic cells carry a variety of cell-surface molecules, some of which are known to have allotypic variation. In rats, the RT7 alloantigenic system has been well documented using alloantisera. We have produced the first mouse hybridoma cell line secreting an antibody, HIS41, which binds to leucocytes of rat strains carrying the RT7.2 but not the RT7.1 determinant. An IgG2b isotype switch variant (HIS41.2b) of the original HIS41 (IgG1 isotype) was also made. HIS41 showed a clear and discrete binding in immunofluorescent and histological experiments and has already been used in several studies on haemopoietic cell turnover and differentiation employing PVG rats congenic for RT7. The present study addresses the question of whether the RT7 gene products are members of the L-CA family, which has been a matter of controversy over the last decade. When using HIS41 for the analysis of tissue distribution and molecular weight of RT7 gene products, a strong similarity was evident with the data reported for the L-CA detected by MRC OX-1 and MRC OX-30. These two MoAb have been reported to bind to all members of the L-CA family. All haemopoietic cells, excluding erythrocytes and the more mature stages of erythropoiesis, stained with HIS41. The molecular weights of HIS41 binding molecules on thymocytes and peripheral T cells were comparable to the L-CA precipitated by MRC OX-1. Capping and sequential immunoprecipitation studies indicated that HIS41 and MRC OX-30-binding molecules were identical. MRC OX-1, however, appeared to bind only a subset of these molecules. Thus, our study confirms the identity of RT7.2 gene products and L-CA. It also revealed a difference between MRC OX-1 and MRC OX-30 not noticed previously.

Effects of sulphydryl reagents on the formation of the aniline metabolite 4-aminophenol and its sulphate and glucuronide conjugates in primary cultures of rat hepatocytes

1. The effects of various sulphydryl-blocking reagents on aniline biotransformation and cytochrome P-450 levels were studied in cultured rat hepatocytes. 2. Exposure of aniline-metabolizing hepatocytes to p-chloro-mercuribenzoate (PCMB) or p-chloromercuribenzenesulphonic acid (PCMBS) resulted in decreased levels of cytochrome P-450, decreased glucuronidation of 4-aminophenol and increased levels of free 4-aminophenol. 3. Incubation of aniline-metabolizing hepatocytes with disulfiram resulted in decreased formation of 4-aminophenol, but this was not associated with impaired glucuronidation or cytochrome P-450 levels. 4. Exposure of aniline-metabolizing hepatocytes to mersalyl, 2,2'-dithiodipyridine (DTP), 6,6'-carboxydipyridine disulphide (CPDS) or N-ethylmaleimide did not affect the biotransformation of aniline or cytochrome P-450 levels. 5. Metyrapone prevented degradation of cytochrome P-450. Exposure of cells to SKF-525 A inhibited aniline biotransformation without altering cytochrome P-450 levels. 6. PCMB and PCMBS inhibited aniline metabolism, probably by binding to a cysteinyl-SH residue in cytochrome P-450 apoenzyme and 'active sites' of UDP-glucuronyl transferases. Disulfiram inhibited aniline biotransformation, probably indirectly by diminishing NADPH.

Interaction between hybrid mouse monoclonal antibodies and the human high-affinity IgG FcR, huFc gamma RI, on U937. Involvement of only one of the mIgG heavy chains in receptor binding

Here we have used hybrid mouse IgG1-2a and IgG2a-2b mAb to demonstrate that the interaction between the human high-affinity IgG FcR (huFc gamma RI) and monomeric mouse IgG2a mAb requires only one of the mIgG2a H chains. Recently, we reported a method for the generation and isolation of hybrid hybridomas, producing hybrid mouse mAb. Using this method we have obtained hybrid mouse (m)IgG1-2a and mIgG2a-2b mAb reacting with either horseradish peroxidase or human IgA1 (monospecific mAb) or with both Ag (bispecific mAb). Using protein A- or Ag-affinity chromatography purified hybrid mAb, we demonstrate here the binding of monomeric hybrid mIgG1-2a and mIgG2a-2b mAb to huFc gamma R on U937 cells, whereas no binding could be observed to the K562 cell line. Monomeric mouse IgG2a mAb and human IgG1 were found to be capable of inhibiting the binding of these hybrid mIgG1-2a and mIgG2a-2b mAb in a manner similar to the way they inhibited binding of monomeric mIgG2a mAb to U937 cells; this is in contrast to our findings for mIgG1 and mIgG2b mAb which did not inhibit the binding of both hybrid mAb. In addition, the binding of the hybrid mIgG1-2a and mIgG2a-2b mAb could be blocked by mAb TB-3, which is known to block huFc gamma RI-mediated binding by the "Kurlander phenomenon" and not by the anti-Fc gamma RII mAb CIKM5 and IV.3. These results indicate that both types of monomeric hybrid mAb are bound by the huFc gamma RI. Scatchard plots of mIgG2a, hybrid mIgG1-2a, and mIgG2a-2b mAb binding revealed similar numbers of binding sites and similar affinity constants of huFc gamma RI for these mAb (0.9 to 3.6 x 10(8) M-1). These results suggest that huFc gamma RI, present on the U937 cell line, are capable of binding monomeric hybrid mIgG1-2a and mIgG2a-2b mAb, and that this interaction requires only one of the mIgG2a H chains.

Interaction between hybrid mouse monoclonal antibodies and the human high-affinity IgG FcR, huFc gamma RI, on U937. Involvement of only one of the mIgG heavy chains in receptor binding

Here we have used hybrid mouse IgG1-2a and IgG2a-2b mAb to demonstrate that the interaction between the human high-affinity IgG FcR (huFc gamma RI) and monomeric mouse IgG2a mAb requires only one of the mIgG2a H chains. Recently, we reported a method for the generation and isolation of hybrid hybridomas, producing hybrid mouse mAb. Using this method we have obtained hybrid mouse (m)IgG1-2a and mIgG2a-2b mAb reacting with either horseradish peroxidase or human IgA1 (monospecific mAb) or with both Ag (bispecific mAb). Using protein A- or Ag-affinity chromatography purified hybrid mAb, we demonstrate here the binding of monomeric hybrid mIgG1-2a and mIgG2a-2b mAb to huFc gamma R on U937 cells, whereas no binding could be observed to the K562 cell line. Monomeric mouse IgG2a mAb and human IgG1 were found to be capable of inhibiting the binding of these hybrid mIgG1-2a and mIgG2a-2b mAb in a manner similar to the way they inhibited binding of monomeric mIgG2a mAb to U937 cells; this is in contrast to our findings for mIgG1 and mIgG2b mAb which did not inhibit the binding of both hybrid mAb. In addition, the binding of the hybrid mIgG1-2a and mIgG2a-2b mAb could be blocked by mAb TB-3, which is known to block huFc gamma RI-mediated binding by the "Kurlander phenomenon" and not by the anti-Fc gamma RII mAb CIKM5 and IV.3. These results indicate that both types of monomeric hybrid mAb are bound by the huFc gamma RI. Scatchard plots of mIgG2a, hybrid mIgG1-2a, and mIgG2a-2b mAb binding revealed similar numbers of binding sites and similar affinity constants of huFc gamma RI for these mAb (0.9 to 3.6 x 10(8) M-1). These results suggest that huFc gamma RI, present on the U937 cell line, are capable of binding monomeric hybrid mIgG1-2a and mIgG2a-2b mAb, and that this interaction requires only one of the mIgG2a H chains.

Functional polymorphisms of Fc receptors in human monocyte-mediated cytotoxicity towards erythrocytes induced by murine isotype switch variants

Human monocytes can be triggered to antibody-dependent cell-mediated cytotoxicity (ADCC) by murine antibodies. In this study, a series of H chain isotype switch variant antibodies against glycophorin A on human RBC was used to study the influence of isotype on the induction of ADCC. Furthermore, it was studied whether the functional heterogeneity in responsiveness to IgG1 and IgG2b anti-CD3 antibodies, as found among different donors in T cell proliferation induction experiments, was reflected in ADCC. Whereas IgG2a induced ADCC to the same extent in monocytes from all donors, IgG1 showed a heterogeneous pattern, which corresponded to the heterogeneity in T cell proliferation studies. IgG1 anti-CD3 nonresponder monocytes could, however, be induced to ADCC by IgG1 antiglycophorin, although they needed a much higher antibody density on the target cell than did responder monocytes. IgG2b antiglycophorin at a high density induced ADCC in monocytes from all donors irrespective of responsiveness to IgG2b anti-CD3, whereas IgE and IgA antiglycophorin were barely effective in monocytes from all donors. By specific blocking with mAb, the FcR that were involved in ADCC directed by the various isotypes were characterized. ADCC by IgG2a was predominantly mediated by FcRI and could be specifically enhanced by culturing the monocytes with rIFN-gamma. ADCC by IgG1 was predominantly mediated through FcRII in both anti-CD3 responder and nonresponder monocytes. FcRII was also involved in ADCC by IgG2b, although other receptors seemed to contribute significantly to ADCC. When FcRII or FcRI were blocked, IgG1 and IgG2a could also functionally interact with FcRI and FcRII, respectively, provided that the target cells were sensitized to a high degree. These findings indicate that FcRI and both forms of FcRII can mediate cytotoxicity and that the specificity of human FcR for murine isotypes is relative.

Induction of tumor-cell lysis by bi-specific monoclonal antibodies recognizing renal-cell carcinoma and CD3 antigen

Bi-specific monoclonal antibodies (MAbs) were developed by somatic hybridization of 2 mouse hybridomas, one producing MAb against the G250 renal-cell carcinoma (RCC)-associated antigen and the other against the T-cell antigen CD3 (OKT3). The dual specificity of the hybrid MAb produced by these so-called quadromas was analyzed by immunohistochemistry on tissue sections and by cytotoxicity assays with relevant target and effector cells. The bi-specific MAb could induce TCR alpha beta/CD3+ and TCR gamma delta/CD3+ cloned lymphocytes to kill RCC cells. A noteworthy finding was that the TCR alpha beta and gamma delta lymphocyte clones showed different triggering abilities. The specificity of target-cell lysis by the cytotoxic T cells (CTL) was dictated by the specificity of the G250 MAb. Control bi-specific MAb, recognizing a cell-surface structure not involved in T-cell activation, did not induce lysis. Several IgG subclass switch variants of the G250 hybridoma, i.e., IgG1, 2a, 2b and IgE, were used for somatic hybridization with the OKT3 hybridoma (IgG2a). Except for IgE, all IgG subclass combinations could equally induce cytolysis. Induction of cytolysis was inhibited only by excess OKT3 MAb. Comparison of 2 bi-specific MAb preparations of the same combination (IgG2a/1), produced by 2 quadromas derived from the same parental hybridomas after identical purification procedures, produced different amounts of bispecific MAb.

Functional polymorphisms of Fc receptors in human monocyte-mediated cytotoxicity towards erythrocytes induced by murine isotype switch variants

Human monocytes can be triggered to antibody-dependent cell-mediated cytotoxicity (ADCC) by murine antibodies. In this study, a series of H chain isotype switch variant antibodies against glycophorin A on human RBC was used to study the influence of isotype on the induction of ADCC. Furthermore, it was studied whether the functional heterogeneity in responsiveness to IgG1 and IgG2b anti-CD3 antibodies, as found among different donors in T cell proliferation induction experiments, was reflected in ADCC. Whereas IgG2a induced ADCC to the same extent in monocytes from all donors, IgG1 showed a heterogeneous pattern, which corresponded to the heterogeneity in T cell proliferation studies. IgG1 anti-CD3 nonresponder monocytes could, however, be induced to ADCC by IgG1 antiglycophorin, although they needed a much higher antibody density on the target cell than did responder monocytes. IgG2b antiglycophorin at a high density induced ADCC in monocytes from all donors irrespective of responsiveness to IgG2b anti-CD3, whereas IgE and IgA antiglycophorin were barely effective in monocytes from all donors. By specific blocking with mAb, the FcR that were involved in ADCC directed by the various isotypes were characterized. ADCC by IgG2a was predominantly mediated by FcRI and could be specifically enhanced by culturing the monocytes with rIFN-gamma. ADCC by IgG1 was predominantly mediated through FcRII in both anti-CD3 responder and nonresponder monocytes. FcRII was also involved in ADCC by IgG2b, although other receptors seemed to contribute significantly to ADCC. When FcRII or FcRI were blocked, IgG1 and IgG2a could also functionally interact with FcRI and FcRII, respectively, provided that the target cells were sensitized to a high degree. These findings indicate that FcRI and both forms of FcRII can mediate cytotoxicity and that the specificity of human FcR for murine isotypes is relative.

Rapid method for the determination and quantification of bromosulphophthalein and metabolites in cultured hepatocytes, culture media and bile by high-performance liquid chromatography

An ion-pair high-performance liquid chromatographic method for the rapid, selective and sensitive analysis of samples containing bromosulphophthalein (BSP) and its conjugates is presented. The method is useful for analysis in bile, culture media and cultured hepatocytes. Two sample preparation methods are described. Even though BSP recovery from albumin binding is complete, only a small percentage of free BSP can be detected in cells, possibly owing to a conjugation-related pool of BSP in cells. As BSP-glutathione recovery is complete, the method offers a useful tool to investigate impairment of glutathione conjugation.

Murine monoclonal isotype switch variants. Detection with rat monoclonal antibodies in ELISA and isolation by sequential sublining

Isotype switch variants, which arise in monoclonal antibody-producing cell lines, can be detected and selected on the basis of sensitive isotype-specific assays. In this study we used a series of enzyme-linked immunosorbent assays specific for murine IgG1, IgG2b, IgG2a, IgE or IgA, which permitted the detection of low frequency switch variants of hybridoma cell lines, irrespective of the specificity of the secreted antibody. In these assays two rat monoclonal antibodies were combined: one specific for the particular heavy-chain isotype, the other for the light-chain isotype, which was identical in all variants. The value of rat monoclonal antibodies for the detection of isotype switch variants is illustrated by the isolation of a series of variant antibodies specific for the CD3 complex present on human T lymphocytes.

Induction of T cell proliferation with anti-CD3 switch-variant monoclonal antibodies: effects of heavy chain isotype in monocyte-dependent systems

Monoclonal antibodies (mAb) directed against the CD3 (T3), antigen are able to induce proliferation in resting human T lymphocytes. T cell proliferation only occurs in the presence of monocytes that carry the proper Fc receptor for the mAb used. To further analyze the role of the Fc portion of anti-CD3 mAb in proliferation induction, we isolated, starting from a gamma 1 anti-CD3-producing hybridoma, four heavy-chain isotype switch-variant antibody-secreting clones, producing gamma 2b, gamma 2a, epsilon and alpha, respectively. All variant antibodies recognize the CD3 antigen as determined by immunoprecipitation and cross-blocking experiments. With this series of isotype variant antibodies we were able, in proliferation induction experiments, to confirm the Fc receptor polymorphism for murine IgG2a, IgG2b and IgG1 on human monocytes. Moreover, we found that all 30 donors tested responded to the IgE anti-CD3 antibody, while no IgA responders could be identified. The induction of proliferation by the IgE variant antibody does not require the 72-kDa Fc receptor which is responsible for the interaction with mouse IgG2a. Nonresponsiveness to the IgG1 antibody, but not to the IgG2b or IgA variant antibodies, could be overcome by the addition of exogenous interleukin 2 to the cultures. When the switch-variant antibodies were used to induce IgM synthesis in peripheral blood mononuclear cells only low IgM synthesis was found, with the exception of the IgE variant, which induced excellent T cell help for IgM production.

Functional studies with anti-CD3 heavy chain isotype switch-variant monoclonal antibodies. Accessory cell-independent induction of interleukin 2 responsiveness in T cells by epsilon-anti-CD3

A series of heavy chain isotype switch-variant anti-CD3 monoclonal antibodies (mAb) was used to study the proliferation requirements of purified T cells. None of the variant antibodies was able by itself to induce proliferation. In the presence of exogenous interleukin 2 (IL-2) strong mitogenesis was observed upon stimulation with epsilon-anti-CD3, whereas gamma 1, gamma 2b, gamma 2a, and alpha-anti-CD3 failed to induce T cell proliferation. All variant antibodies induced vigorous proliferation in combination with phorbol myristate acetate. Purified T cells, cultured in the presence of epsilon-anti-CD3, in the absence of IL-2, did not express detectable amounts of TAC-antigen (CD25). The binding of the variant antibodies to the CD3 antigen was evaluated in cross-blocking experiments. It was demonstrated that the epsilon-anti-CD3 antibody, in comparison with the other variant mAb, has a relatively low avidity for the CD3 antigen. In modulation experiments, the IgE variant antibody was unable to induce a substantial loss of CD3 antigen. T cell triggering was investigated at the level of Ca2+ mobilization by means of the dye Indo-1. In contrast to the gamma 1, gamma 2b, gamma 2a, and alpha mAb, which induced a rapid and high rise in the free intracellular calcium level, epsilon-anti-CD3 caused a slow and low rise. These studies indicate that the epsilon-anti-CD3 antibody has a low avidity for the CD3 antigen, compared with the other variant mAb, possibly as a result of monovalent binding. Apparently, the avidity and/or valency of CD3 antigen binding not only has a major influence on CD3 modulation and anti-CD3-induced Ca2+ mobilization, but also sets T cell requirements for IL-2 responsiveness.

Functional studies with anti-CD3 heavy chain isotype switch-variant monoclonal antibodies. Accessory cell-independent induction of interleukin 2 responsiveness in T cells by epsilon-anti-CD3

A series of heavy chain isotype switch-variant anti-CD3 monoclonal antibodies (mAb) was used to study the proliferation requirements of purified T cells. None of the variant antibodies was able by itself to induce proliferation. In the presence of exogenous interleukin 2 (IL-2) strong mitogenesis was observed upon stimulation with epsilon-anti-CD3, whereas gamma 1, gamma 2b, gamma 2a, and alpha-anti-CD3 failed to induce T cell proliferation. All variant antibodies induced vigorous proliferation in combination with phorbol myristate acetate. Purified T cells, cultured in the presence of epsilon-anti-CD3, in the absence of IL-2, did not express detectable amounts of TAC-antigen (CD25). The binding of the variant antibodies to the CD3 antigen was evaluated in cross-blocking experiments. It was demonstrated that the epsilon-anti-CD3 antibody, in comparison with the other variant mAb, has a relatively low avidity for the CD3 antigen. In modulation experiments, the IgE variant antibody was unable to induce a substantial loss of CD3 antigen. T cell triggering was investigated at the level of Ca2+ mobilization by means of the dye Indo-1. In contrast to the gamma 1, gamma 2b, gamma 2a, and alpha mAb, which induced a rapid and high rise in the free intracellular calcium level, epsilon-anti-CD3 caused a slow and low rise. These studies indicate that the epsilon-anti-CD3 antibody has a low avidity for the CD3 antigen, compared with the other variant mAb, possibly as a result of monovalent binding. Apparently, the avidity and/or valency of CD3 antigen binding not only has a major influence on CD3 modulation and anti-CD3-induced Ca2+ mobilization, but also sets T cell requirements for IL-2 responsiveness.

Monoclonal anti-peroxidase isotype switch variants. Applications in studies of protein A binding and characterization of rat monoclonal antibodies

A series of heavy chain isotype switch variants was derived from a hybridoma cell line secreting monoclonal antibodies specific for horseradish peroxidase. By the combined use of sensitive isotype-specific ELISAs and sequential sublining IgG2b, IgG2a, IgE and Iga anti-peroxidase-producing variants were successively isolated out of IgG1-secreting parental cells. The anti-peroxidase isotype variant antibodies are particularly appropriate for use in studies of the influence of heavy chain isotype in the effector functions of immunoglobulins. The use of variant antibodies with specificity for an enzyme favors their application in immunoassays because an enzyme-conjugated second antibody is not needed. Here we describe two applications of the anti-peroxidase switch variants. First, the variants are compared with respect to their affinity for Staphylococcus protein A. While IgG1 anti-peroxidase showed weak binding, both IgG2 variants strongly bound to protein A, whereas IgE and IgA variants had no affinity for protein A. Next, the switch variants were used to determine the isotype specificity of rat monoclonal antibodies generated to murine IgE.