Evaluation of in vitro Assays to Assess the Modulation of Dendritic Cells Functions by Therapeutic Antibodies and Aggregates

Therapeutic antibodies have the potential to induce immunogenicity leading to the development of anti-drug antibodies (ADA) that consequently may result in reduced serum drug concentrations, a loss of efficacy or potential hypersensitivity reactions. Among other factors, aggregated antibodies have been suggested to promote immunogenicity, thus enhancing ADA production. Dendritic cells (DC) are the most efficient antigen-presenting cell population and are crucial for the initiation of T cell responses and the subsequent generation of an adaptive immune response. This work focuses on the development of predictive in vitro assays that can monitor DC maturation, in order to determine whether drug products have direct DC stimulatory capabilities. To this end, four independent laboratories aligned a common protocol to differentiate human monocyte-derived DC (moDC) that were treated with either native or aggregated preparations of infliximab, natalizumab, adalimumab, or rituximab. These drug products were subjected to different forms of physical stress, heat and shear, resulting in aggregation and the formation of subvisible particles. Each partner developed and optimized assays to monitor diverse end-points of moDC maturation: measuring the upregulation of DC activation markers via flow cytometry, analyzing cytokine, and chemokine production via mRNA and protein quantification and identifying cell signaling pathways via quantification of protein phosphorylation. These study results indicated that infliximab, with the highest propensity to form aggregates when heat-stressed, induced a marked activation of moDC as measured by an increase in CD83 and CD86 surface expression, IL-1β, IL-6, IL-8, IL-12, TNFα, CCL3, and CCL4 transcript upregulation and release of respective proteins, and phosphorylation of the intracellular signaling proteins Syk, ERK1/2, and Akt. In contrast, natalizumab, which does not aggregate under these stress conditions, induced no DC activation in any assay system, whereas adalimumab or rituximab aggregates induced only slight parameter variation. Importantly, the data generated in the different assay systems by each partner site correlated and supported the use of these assays to monitor drug-intrinsic propensities to drive maturation of DC. This moDC assay is also a valuable tool as an in vitro model to assess the intracellular mechanisms that drive DC activation by aggregated therapeutic proteins.

The transferability from rat subacute 4-week oral toxicity study to translational research exemplified by two pharmaceutical immunosuppressants and two environmental pollutants with immunomodulating properties

Exposure to chemicals may have an influence on the immune system. Often, this is an unwanted effect but in some pharmaceuticals, it is the intended mechanism of action. Immune function tests and in depth histopathological investigations of immune organs were integrated in rodent toxicity studies performed according to an extended OECD test guideline 407 protocol. Exemplified by two immunosuppressive drugs, azathioprine and cyclosporine A, and two environmental chemicals, hexachlorobenzene and benzo[a]pyrene, results of subacute rat studies were compared to knowledge in other species particular in humans. Although immune function has a high concordance in mammalian species, regarding the transferability from rodents to humans various factors have to be taken into account. In rats, sensitivity seems to depend on factors such as strain, sex, stress levels as well as metabolism. The two immunosuppressive drugs showed a high similarity of effects in animals and humans as the immune system was the most sensitive target in both. Hexachlorobenzene gave an inconsistent pattern of effects when considering the immune system of different species. In some species pronounced inflammation was observed, whereas in primates liver toxicity seemed more obvious. Generally, the immune system was not the most sensitive target in hexachlorobenzene-treatment. Immune function tests in rats gave evidence of a reaction to systemic inflammation rather than a direct impact on immune cells. Data from humans are likewise equivocal. In the case of benzo[a]pyrene, the immune system was the most sensitive target in rats. In the in vitro plaque forming cell assay (Mishell-Dutton culture) a direct comparison of cells from different species including rat and human was possible and showed similar reactions. The doses in the rat study had, however, no realistic relation to human exposure, which occurs exclusively in mixtures and in a much lower range. In summary, a case by case approach is necessary when testing immunotoxicity. Improvements for the translation from animals to humans related to immune cells can be expected from in vitro tests which offer direct comparison with reactions of human immune cells. This may lead to a better understanding of results and variations seen in animal studies.

Integrated analysis of toxicity data of two pharmaceutical immunosuppressants and two environmental pollutants with immunomodulating properties to improve the understanding of side effects-A toxicopathologist׳s view

Data in a toxicity test are evaluated generally per parameter. Information on the response per animal in addition to per parameter can improve the evaluation of the results. The results from the six studies in rats, described in the paper by Kemmerling, J., Fehlert, E., Rühl-Fehlert, C., Kuper, C.F., Stropp, G., Vogels, J., Krul, C., Vohr, H.-W., 2015. The transferability from rat subacute 4-week oral toxicity study to translational research exemplified by two pharmaceutical immunosuppressants and two environmental pollutants with immunomodulating properties (In this issue), have been subjected to principal component analysis (PCA) and principal component discriminant analysis (PC-DA). The two pharmaceuticals azathioprine (AZA) and cyclosporine A (CSA) and the two environmental pollutants hexachlorobenzene (HCB) and benzo(a)pyrene (BaP) all modulate the immune system, albeit that their mode of immunomodulation is quite diverse. PCA illustrated the similarities between the two independent studies with AZA (AZA1 and AZA2) and CSA (CSA1 and CSA2). The PC-DA on data of the AZA2 study did not increase substantially the information on dose levels. In general, the no-effect levels were lower upon single parameter analysis than indicated by the distances between the dose groups in the PCA. This was mostly due to the expert judgment in the single parameter evaluation, which took into account outstanding pathology in only one or two animals. The PCA plots did not reveal sex-related differences in sensitivity, but the key pathology for males and females differed. The observed variability in some of the control groups was largely a peripheral blood effect. Most importantly, PCA analysis identified several animals outside the 95% confidence limit indicating high-responders; also low-to-non-responders were identified. The key pathology enhanced the understanding of the response of the animals to the four model compounds.

Performance standards and alternative assays: practical insights from skin sensitization

To encourage the development and validation of alternative toxicity test methods, the effort required for validation of test methods proposed for regulatory purposes should be minimized. Performance standards (PS) facilitate efficient validation by requiring limited testing. Based on the validated method, PS define accuracy and reliability values that must be met by the new similar test method. The OECD adopted internationally harmonized PS for evaluating new endpoint versions of the local lymph node assay (LLNA). However, in the process of evaluating a lymph node cell count alternative (LNCC), simultaneous conduct of the regulatory LLNA showed that this standard test may not always perform in perfect accord with its own PS. The LNCC results were similar to the concurrent LLNA. Discrepancies between PS, LLNA and LNCC were largely associated with "borderline" substances and the variability of both endpoints. Two key lessons were learned: firstly, the understandable focus on substances close to the hazard classification borderline are more likely to emphasise issues of biological variability, which should be taken into account during the evaluation of results; secondly, variability in the results for the standard assay should be considered when selecting reference chemicals for PS.

International Pig-a gene mutation assay trial: evaluation of transferability across 14 laboratories

A collaborative international trial was conducted to evaluate the reproducibility and transferability of an in vivo mutation assay based on the enumeration of CD59-negative rat erythrocytes, a phenotype that is indicative of Pig-a gene mutation. Fourteen laboratories participated in this study, where anti-CD59-PE, SYTO 13 dye, and flow cytometry were used to determine the frequency of CD59-negative erythrocytes (RBC(CD59-)) and CD59-negative reticulocytes (RET(CD59-)). To provide samples with a range of mutant phenotype cell frequencies, male rats were exposed to N-ethyl-N-nitrosourea (ENU) via oral gavage for three consecutive days (Days 1-3). Each laboratory studied 0, 20, and 40 mg ENU/kg/day (n = 5 per group). Three sites also evaluated 4 mg/kg/day. At a minimum, blood samples were collected three times: predosing and on Days 15 and 30. Blood samples were processed according to a standardized sample processing and data acquisition protocol, and three endpoints were measured: %reticulocytes, frequency of RET(CD59-) , and frequency of RBC(CD59-) . The methodology was found to be reproducible, as the analysis of technical replicates resulted in experimental coefficients of variation that approached theoretical values. Good transferability was evident from the similar kinetics and magnitude of the dose-related responses that were observed among different laboratories. Concordance correlation coefficients showed a high level of agreement between the reference site and the test sites (range: 0.87-0.99). Collectively, these data demonstrate that with adequate training of personnel, flow cytometric analysis is capable of reliably enumerating mutant phenotype erythrocytes, thereby providing a robust in vivo mutation assay that is readily transferable across laboratories.

Report on stage III Pig-a mutation assays using benzo[a]pyrene

Genotoxicity assays were conducted on rats treated with benzo[a]pyrene (BaP) as part of Stage III of a validation study on the Pig-a gene mutation assay. Assays were performed at the U.S. FDA-NCTR and Bayer-Germany. Starting on Day 1, groups of five 6- to 7-week-old male Fischer 344 (F344, used at FDA-NCTR) and Han Wistar rats (Bayer) were given 28 daily doses of 0, 37.5, 75, or 150 mg/kg BaP; blood was sampled on Days -1, 4, 15, 29, and 56. Pig-a mutant frequencies were determined on Days -1, 15, 29, and 56 in total red blood cells (RBCs) and reticulocytes (RETs) as RBC(CD59-) and RET(CD59-) frequencies; percent micronucleated-RETs (%MN-RET) were measured on Days 4 and 29. RBC(CD59-) and RET(CD59-) frequencies increased in a dose- and time-dependent manner, producing significant increases by Day 29 in both rat models. The responses for RETs were stronger than those for RBCs, and the responses in F344 rats were stronger than in Han Wistar rats. BaP also produced significant increases in %MN-RET frequency at Days 4 and 29, with the responses being greater in F344 than Han Wistar rats. The overall findings were consistent with those of the reference laboratory using Han Wistar rats. Finally, mutation assays performed on splenocytes from Day 56 F344 rats indicated that BaP mutant frequencies were three to fivefold higher for the Hprt gene than the Pig-a gene. The results indicate that the Pig-a RET and RBC assays are reproducible, transferable, and show promise for integrating gene mutation into 28-day repeat-dose studies.

Testosterone response of hepatic gene expression in female mice having acquired testosterone-unresponsive immunity to Plasmodium chabaudi malaria

Blood-stage malaria of Plasmodium chabaudi is characterized by its responsiveness to testosterone (T): T suppresses development of protective immunity, whereas once acquired immunity is T-unresponsive. Here, we have analyzed the liver, a T target and lymphoid organ with anti-malaria activity, for its T-responsiveness of gene expression in immune mice. Using Affymetrix microarray technology, in combination with quantitative RT-PCR, we have identified (i) T-unresponsive expression of newly acquired mRNAs encoding diverse sequences of IgG- and IgM-antibodies, (ii) 24 genes whose expression has become T-unresponsive including those encoding the T(H)2 response promoting EHMT2 and the erythrocyte membrane protein band 7.2 STOM, (iii) T-unresponsive expression of mRNAs for the cytokines IL-1β, IL-6, TNFα, and IFNγ, as well as iNOS, which are even not inducible by infection, and (iv) 35 genes retaining their T-responsiveness, which include those encoding the infection-inducible acute phase proteins SAA1, SAA2, and ORM2 as well as those of liver metabolism which encode the T-downregulated female-prevalent enzymes CYP2B9, CYP2B13, CYP3A41, CYP7A1, and SULT2A2 and the T-upregulated male-prevalent enzymes CYP2D9, CYP7B1, UGT2B1, HSD3B2, HSD3B5, respectively. The mRNA of the latter T-metabolizing enzyme is even 5-fold increased by T, suggesting a decrease in the effective T concentrations in the liver of immune mice. Collectively, our data suggest that the liver, which has acquired a selective T-unresponsiveness of gene expression, contributes to the acquired T-unresponsive, antibody-mediated protective immunity to blood-stage malaria of P. chabaudi.

Testosterone-induced permanent changes of hepatic gene expression in female mice sustained during Plasmodium chabaudi malaria infection

Testosterone has been previously shown to induce persistent susceptibility to Plasmodium chabaudi malaria in otherwise resistant female C57BL/6 mice. Here, we investigate as to whether this conversion coincides with permanent changes of hepatic gene expression profiles. Female mice aged 10-12 weeks were treated with testosterone for 3 weeks; then, testosterone treatment was discontinued for 12 weeks before challenging with 10⁶ P. chabaudi-infected erythrocytes. Hepatic gene expression was examined after 12 weeks of testosterone withdrawal and after subsequent infection with P. chabaudi at peak parasitemia, using Affymetrix microarrays with 22 ,690 probe sets representing 14, 000 genes. The expression of 54 genes was found to be permanently changed by testosterone, which remained changed during malaria infection. Most genes were involved in liver metabolism: the female-prevalent genes Cyp2b9, Cyp2b13, Cyp3a41, Cyp3a44, Fmo3, Sult2a2, Sult3a1, and BC014805 were repressed, while the male-prevalent genes Cyp2d9, Cyp7b1, Cyp4a10, Ugt2b1, Ugt2b38, Hsd3b5, and Slco1a1 were upregulated. Genes encoding different nuclear receptors were not persistently changed. Moreover, testosterone induced persistent upregulation of genes involved in hepatocellular carcinoma such as Lama3 and Nox4, whereas genes involved in immune response such as Ifnγ and Igk-C were significantly decreased. Our data provide evidence that testosterone is able to induce specific and robust long-term changes of gene expression profiles in the female mouse liver. In particular, those changes, which presumably indicate masculinized liver metabolism and impaired immune response, may be critical for the testosterone-induced persistent susceptibility of mice to P. chabaudi malaria.

A European inter-laboratory pre-validation of in vitro assays to evaluate immunotoxicity (47.18)

The new European Union REACH (Registration, Evaluation and Authorisation of new and existing CHemicals) policy will increase the use of laboratory animals if alternative methods are not available. The immune system is a target for many chemicals and drugs, with potential adverse effects on human health. We performed an inter-laboratory pre-validation of a set of in vitro assays to detect immunosuppressive capacity.

Human PBMC and murine and rat splenocytes were used. Six immunosuppressive compounds (benzo(a)pyrene, cyclophosphamide, methotrexate, rapamycin, dexamethasone, and urethane) and one non-immunosuppressive compound (D-mannitol) were tested. Basal cytotoxicity was assessed by measuring LDH-release. Human PBMC were stimulated with anti-CD3/anti-CD28, murine splenocytes with anti-CD3/anti-CD28, Con A, LPS, and anti-CD40/IL-4, and rat splenocytes with Con A and LPS. Cell proliferation and IFN-γ and TNF-α production were measured.

Five out of 6 immunosuppressive compounds could be identified as such, and the non-immunotoxic one came out as negative. This suggests that in vitro assays are able to detect immunosuppressive capacity. The sensitivity of the various species/stimulant/endpoint combinations ranged between 38 and 61%, while the specificity ranged between 67 and 100%. This suggests that from these results a choice for specific species/stimulant/endpoint combinations cannot be made.

In vitro tests to evaluate immunotoxicity: A preliminary study

The implementation of Registration, Evaluation and Authorisation of new and existing Chemicals (REACH) will increase the number of laboratory animals used, if alternative methods will not be available. In the meantime, REACH promotes the use of in vitro tests and, therefore, a set of appropriated alternative testing methods and assessment strategies are needed. The immune system can be a target for many chemicals including environmental contaminants and drugs with potential adverse effects on human health. The aim of this study was to evaluate the predictivity of a set of in vitro assays to detect immunosuppression. The tests have been performed on human, rat and murine cells. Different endpoints have been assessed: cytotoxicity, cytokine release, myelotoxicity and mitogen responsiveness. For each of these endpoints IC50s values have been calculated. Six chemical substances, representative of the full range of in vivo responses and for which good human and/or animal data are available either from databases or literature, have been selected: two chemicals classified as not immunotoxic (Urethane and Furosemide), and four (tributyltin chloride (TBTC), Verapamil, Cyclosporin A, Benzo(a)pyrene) with different effect on immune system. All the tests confirmed the strong immunotoxic effect of TBTC as well as they confirmed the negative controls. For one chemical (Verapamil) the IC50 is similar through the different tests. The IC50s obtained with the other chemicals depend on the endpoints and on the animal species. The clonogenic test (CFU-GM) and the mitogen responsiveness showed similar IC50s between human and rodent cells except for Cyclosporin A and TBTC. All different tests classified the compounds analyzed in the same way.

Characterization of primary rat proximal tubular cells by gene expression analysis

The kidney plays a major role in excretory and reabsorptive processes. The kidney cortex consists primarily of proximal tubular cells, which are epithelial cells that are often involved in the induction and progression of various kidney diseases. Therefore primary proximal tubular cells are widely used as a renal cell model. To further characterize this kidney in vitro model different time points in culture after isolation of the cells were compared to the cortex in vivo using gene expression analysis based on microarrays. This study revealed that many metabolic pathways and some kidney-specific functions are lacking in the in vitro model. Furthermore genes involved in RNA and protein synthesis, intracellular transport, extracellular matrix and cytoskeletal organization were upregulated in culture compared to in vivo, indicating proliferation of the cells and differentiation into a cell culture phenotype. The data represented here may help to evaluate the in vivo relevance of results obtained with this in vitro model.

Evaluation of phototoxic and photoallergic potentials of 13 compounds by different in vitro and in vivo methods

Phototoxic side effects of pharmaceutical and cosmetic products are of increasing concern for patients, dermatologists and the chemical industry. Moreover, the need of new chemicals and drugs puts pressure on pre-clinical test methods for side effects, especially interactive adverse-effects with UV-light. So, the predictive potential of different established test methods, which are used regularly in our departments in order to detect the phototoxic potential of chemicals, were analyzed. Namely the fibroblast 3T3 test, the photo hen's egg test, a guinea pig test for measuring acute photoreactions, and a modified Local Lymph Node Assay, the Integrated Model for the Differentiation of Skin Reactions. Various agents with different photoreactive potential were tested: quinolones like Bay y 3118, ciprofloxacin, enoxacin, lomefloxacin, moxifloxacin, ofloxacin, sparfloxacin, as well as promethazine, chlorpromazine, 8-methoxypsoralen and olaquindox serving as control. Special emphasis was taken to evaluate the capability of the employed test procedures to predict phototoxic side effects in patients. Following our results, both in vitro assays were useful tools to detect photoirritancy while the photoallergic potentials of tested compounds were exclusively detected by an in vivo assay. As long as no in vitro model for photoallergy is available, the UV-IMDS should be considered to evaluate photoallergic properties of a supposed photoreactive agent.

Local lymph node assay with non-radioisotope alternative endpoints

The local lymph node assay has recently been accepted by regulatory agencies as a stand-alone alternate method for predicting allergic contact dermatitis. To compare the sensitivity of non-radioisotope methods with that of the standard assay, we determined if these modified methods would affect evaluation of sensitization potency. For this reason, we used 2,4-dinitrochlorobenzene (DNCB) and benzocaine for different sensitizing criteria. Female CBA mice were treated for 3 days with a test compound or vehicle applied to each side of both ears. Bilateral auricular lymph node proliferative activity was assessed by the following endpoints with incorporation of 3H-methyl thymidine (3H-TdR), bromodeoxyuridine (BrdU) in vivo, and BrdU ex vivo, IL-2 production, and proliferating cell nuclear antigen (PCNA) expression. Ear thickness was also tested. The strong sensitizer DNCB was detectable by any of the non-radioisotope endpoints as well as by radioisotope-dependent standard assay. On the other hand, when evaluating the weak sensitizer benzocaine, significant changes were evident in BrdU incorporation ex vivo and in vivo, and IL-2 production. We believe that these non-radioisotope methods can assess allergic contact dermatitis caused by chemicals even in the laboratory, where it can be difficult to handle radioisotopes.

Respiratory hypersensitivity to trimellitic anhydride in Brown Norway rats: a comparison of endpoints

A rat bioassay has been developed to provide an objective approach for the identification and classification of respiratory allergy using trimellitic anhydride (TMA), which is a known respiratory tract irritant and asthmagen. Particular emphasis was placed on the study of route-of-induction-dependent effects and their progression upon inhalation challenge with TMA (approximately 23 mg m(-3) for a duration of 30 min), which included analysis of specific and non-specific airway hyperreactivity and pulmonary inflammation initiated and sustained by immunological processes. Refinement of the bioassay focused on procedures to probe changes occurring upon challenge with TMA or methacholine aerosols using physiological, biochemical and immunological procedures. Following challenge with TMA, the rats sensitized to TMA showed marked changes in peak inspiratory and expiratory air flows and respiratory minute volume. In these animals, a sustained pulmonary inflammation occurred, characterized by specific endpoints determined in bronchoalveolar lavage (lactate dehydrogenase, protein, nitrite, eosinophil peroxidase, myeloperoxidase). When compared with the naive controls, lung weights were increased significantly, as were the weights of lung-associated lymph nodes following inhalation induction and auricular lymph nodes following topical induction. The extent of changes observed was equal or more pronounced in animals sensitized epicutaneously (day 0:150 microl vehicle/50% TMA on each flank, day 7; booster administration to the skin of the dorsum of both ears using half the concentration and volume used on day 0) when compared with rats sensitized by 5 x 3 h day(-1) inhalation exposures (low dose: 25 mg TMA m(-3), high dose: 120 mg TMA m(-3)). In summary, the findings support the conclusion that the Brown Norway rat model is suitable for identifying TMA as an agent that causes both an immediate-type change of breathing patterns and a delayed-type sustained pulmonary inflammatory response. However, it remains unresolved whether the marked effects observed in the topically sensitized rats are more related to a route-of-induction or dose-dependent phenomenon.

Cytokine expression profiles during murine contact allergy: T helper 2 cytokines are expressed irrespective of the type of contact allergen

We have investigated the cytokine response pattern following sensitisation (induction) of BALB/c mice with different chemicals (dinitrochlorobenzene, dinitrofluorobenzene, oxazolone, glutaraldehyde, formaldehyde, trimellitic anhydride, croton oil) and elicitation (challenge) of contact allergy in sensitised animals. The results of our investigations showed that different chemicals induced both T helper (Th) 1 cytokines [interleukin (IL) 2, interferon beta (IFNgamma) [corrected] and Th2 cytokines (IL-4, IL-10) at different stages during murine contact allergy. We also confirmed our previous findings that IL-4 and IL-10 release were up-regulated during the challenge phase regardless the contact allergen used, whereas the release of IFNgamma [corrected] did not show a clear preference for being up- or down-regulated. In our hands, the increased expression of Th2 cytokines after challenge exposure to contact allergens appeared as a stable marker of secondary contact allergenic responses. Quantitative differences in the expression of IL-4 were observed between different contact allergens. The present results clearly indicate that skin sensitisers were able to elicit cytokine response patterns, which could not be related to a clear-cut Th1 or Th2 type of cytokine response. Furthermore, dermal application of contact allergens produced different kinetics of cytokine secretion upon induction and challenge. In our hands, the co-expression of Th1 and Th2 type cytokines appeared as a universal consequence of dermal application of contact allergens to responsive mice. Our results indicate that co-expression of Th1 and Th2 cytokines during contact allergy is an important feature of murine contact allergy in responsive mice and that chemicals differ in their potency to induce the expression of these cytokines. Furthermore, the results do not support the view that different chemicals induce Th1 or Th2 cytokines in a mutually exclusive manner depending on their preference for inducing either contact or respiratory allergy. The results are expected to renew the discussion about the usefulness of the Th1/Th2 paradigm in certain areas of immunotoxicology.

Industry experience in the identification of the immunotoxic potential of agrochemicals

During recent years immunotoxicity has been increasingly recognized as an important endpoint in rodent short-time studies. This has been documented by FDA, OECD, and just recently in a new EPA guideline. This guideline is confined to the immunosuppressive effects of chemicals. Various parameters to detect immunotoxic effects exist, including cell counts, cell subpopulation analysis, functional tests, and/or advanced pathology. Their validity in detecting immunotoxic effects has been demonstrated to different degrees. Our experience with some of these parameters is reported here. Due to the recommendation of the guideline, it is necessary to differentiate from the context of the study data between primary and secondary immunotoxicity, the latter being an unspecific sequel of toxicity to other organs. In our studies, we found examples for both mechanisms. For primary immunotoxic substances, immunosuppression is markedly more frequent than immunostimulation, although primary effects, on the whole, occur relatively seldom during toxicological screening. In both cases, we found a good correlation between cell analysis and functional parameters on one hand and pathology on the other, thus warranting that overt immunotoxicity would not remain undetected in routine studies with high dose levels. However, the higher predictivity of functional parameters and the analysis of special subpopulations is necessary for the determination of the no-effect level and for fine differentiation during the screening of comparable immunotoxic compounds. Cyclosporin A is an example for the former, and the screening of different agrochemicals is an example for the latter aspect. As verified by the collaboration studies, an advanced histopathology of lymphoid organs, combined with flow cytometry of immune competent cells and a functional assay, is able to discriminate between primary and secondary effects as well as immunosuppression and immunostimulation, and thus to identify an immunotoxic hazard.

Analyses of cutaneous fluoroquinolones photoreactivity using the integrated model for the differentiation of skin reactions

Currently available test models for the differentiation of photoallergic and photoirritant reactions are extremely time consuming and the protocols are very heterogeneous. In vitro tests are of proven value in predicting irritant or toxic effects, but these tests fail to predict chemical-induced allergic side effects. We developed test systems for this endpoint which is not easily detected by existing assays. In a previous publication we were able to discriminate between a contact sensitizer and a skin irritant with a combination of primary ear swelling analysis and cell counting of the ear-draining lymph nodes [Toxicol. Appl. Pharm. 153 (1998) 83; Arch. Toxicol. 73 (2000) 501]. This combination of tests was called the Integrated Model for the Differentiation of chemical-induced allergic and irritant Skin reactions (IMDS). In addition, it had been shown before that inclusion of UV irradiation in the local lymph node assay enables discrimination of photoallergic from photoirritant reactions after dermal application [Photodermatol. Photoimmunol. Photomed. 10 (1994) 57]. Because of the fact that fluoroquinolones are known to induce photoreactions after oral but not dermal treatment, the aim of the present study was to apply the IMDS for the fast and reliable differentiation of photoreactions due to fluoroquinolones after oral treatment. Enoxacin, lomefloxacin, ofloxacin, sparfloxacin and BAY y 3118 were tested in this system. We found a good correlation between the results of UV light-irradiated IMDS and a guinea pig model with the quinolones as far as photoirritancy was concerned. This holds true also for the photoallergic standard olaquindox and the photoirritant standard 8-methoxypsoralen. However, in contrast to the guinea pig assays the IMDS is fast and extremely predictive for the risk of both photosensitization and photoirritancy depending on the route of exposure. Thus, the UV light-irradiated IMDS turned out to be a good tool for the preclinical risk assessment procedure in terms of discriminating photoreactions. In addition, flow cytometric analyses were used to underline the fact that antigen-independent activation occurred after the induction of photoirritant reactions.

An intra-laboratory validation of the Integrated Model for the Differentiation of Skin Reactions (IMDS): discrimination between (photo)allergic and (photo)irritant skin reactions in mice

We recently presented a modified local lymph node test which made it possible to quickly and reliably differentiate between irritative and allergic skin reactions with extremely simple parameters. The Integrated Model for the Differentiation of Skin Reactions (IMDS) test combines measurement of cell proliferation in draining lymph nodes with measurement of primary ear swelling after topical application of the test substance on three consecutive days. In contrast to the 'classic' skin sensitisation test in guinea-pigs the IMDS test is considerably faster and is based on objective measured data, not subjective skin evaluations. Like the Local Lymph Node Assay (LLNA), measurement of allergic potential in the IMDS test is based on the underlying immunological mechanisms, but also considers the behaviour of immune competent cells following non-specific activation by irritants. In addition, the IMDS test can employ UV radiation after application of the substance and, therefore, make differentiation possible between different types of skin photoreaction (photoallergy and photoirritation) after both topical and systemic administration. Attempts to achieve this kind of discrimination with the LLNA necessitate considerably greater expenditure, as proliferation in the draining lymph nodes can also be induced by moderate to extreme (photo)irritants. In a previous paper in which we presented the IMDS test, we examined each type of reaction in reference to one single standard; the next logical step was therefore a broad-based intra-laboratory validation. An important factor in the validation was the use of standards that had been thoroughly examined in both guinea pig and mouse systems and were also relevant with regard to estimation of the risk for humans. The data presented here show that the IMDS is a simple and reliable tool for obtaining fast and reproducible assessments of potential (photo)allergic and (photo)irritant skin reactions to substances.

Mouse popliteal lymph node assay for assessment of allergic and autoimmunity-inducing potentials of low-molecular-weight drugs

In the present collaborative study, popliteal lymph node (PLN) responses to penicillin G (an allergenic chemical), D-penicillamine (an autoimmunity-inducing chemical), and barbital (a negative reference chemical) were investigated in three different mouse strains by ten pharmaceutical companies. Two inbred mouse strains (BALB/c and A/J) and one outbred strain (ICR) were subcutaneously injected with saline solutions containing penicillin G (1.25, 2.5 and 5 mg/mouse), D-penicillamine (0.5, 1 and 2 mg/mouse), or barbital (2 mg/mouse) into one hind footpad and saline only was injected into the contralateral footpad. PLN cellularity indices were determined on day 7. In the three strains tested, the penicillin G and D-penicillamine injections resulted in approximately dose-dependent responses. In contrast, barbital failed to generate a significant PLN reaction. In the typical data from one of the participating laboratories, the PLN responses of A/J, BALB/c, and ICR to penicillin G were high, intermediate and low, respectively, while their PLN responses to D-penicillamine were all high. Some variation in PLN cellularity indices was observed among the participating laboratories, but reproducibility of the popliteal lymph node assay (PLNA) evaluation was partly confirmed. Although the appropriate selection of mouse strains and drug dosage levels has to be considered, these results suggest that the PLNA may be an appropriate screening system for prediction of the allergic or autoimmunity-inducing potentials of low-molecular-weight drugs.

An integrated model for the differentiation of chemical-induced allergic and irritant skin reactions

Contact and photocontact allergic as well as irritant and photoirritant skin reactions represent a major problem in clinical dermatology and during the development of new pharmaceuticals. Furthermore, there is a lack of in vitro and in vivo assays that provide a clear differentiation between allergic and irritant skin reactions. Here, we describe an integrated model to differentiate between chemical-induced allergic and irritant skin reactions by measuring objective and easy-to-determine parameters within both skin and skin-draining lymph nodes. Dose-response studies with standard contact and photocontact allergens as well as irritants and photoirritants revealed that irritants predominantly induced skin inflammation, which in turn stimulated draining lymph node cell proliferation. In contrast, the induction phase of contact or photocontact allergy was characterized by marginal skin inflammation, but a marked activation and proliferation of skin-draining lymph node cells. Therefore, a differentiation index (DI) was defined describing the relation between skin-draining lymph node cell activation (lymph node cell count index) and skin inflammation (ear swelling). A DI > 1 indicates an allergic reaction pattern whereas DI < 1 demonstrates an irritant potential of a chemical. Experiments with the contact allergen oxazolone, the photocontact allergen TCSA + UVA, the irritant croton oil, and the photoirritant 8-methoxypsoralen + UVA confirmed the predictive value of DI. Furthermore, flow cytometric analysis of lymph node-derived T- and B-cell subpopulations revealed that contact sensitizer, but not irritant, induced the expression of CD69 on the surface of I-A+ cells. In conclusion, further studies with a broad range of irritants and allergens will be required to confirm general applicability.

Topical FK506 Suppresses Cytokine and Costimulatory Molecule Expression in Epidermal and Local Draining Lymph Node Cells During Primary Skin Immune Responses

Recently, it has been shown that the immunosuppressive macrolide lactone, FK506, exerts good therapeutic efficacy in inflammatory skin diseases. The aim of this study was to analyze the influence of topical FK506 on molecular (IL-1α, IL-1β, IL-2, IL-4, IL-12 p35, IL-12 p40, macrophage inflammatory protein-2 (MIP-2), granulocyte-macrophage CSF (GM-CSF), TNF-α, and IFN-γ) and cellular (I-A+/CD80+, I-A+/CD54+, I-A+/CD69+, I-A+/B220+, and CD4+/CD25+) events in epidermal (EC) and local draining lymph node (LNC) cells during primary contact hypersensitivity responses. Cytokine mRNA levels for IL-1α, IL-1β, GM-CSF, TNF-α, MIP-2, and IFN-γ in EC and for IL-2, IL-4, IL-12 p35, IL-12 p40, and IFN-γ in LNC were increased and resulted in significant LNC proliferation during oxazolone-induced contact hypersensitivity. Topical FK506 treatment dose-dependently suppressed oxazolone-induced LNC proliferation. This effect was correlated with decreased IL-1α, IL-1β, GM-CSF, TNF-α, MIP-2, and IFN-γ mRNA expression within the epidermis and decreased IL-12 p35 and p40 mRNA expression in LNC. Further analysis of the LNC cytokine pattern revealed that the production of both Th1 (IFN-γ and IL-2) and Th2 (IL-4) cytokines was dramatically impaired after topical FK506 treatment. Flow cytometric analysis showed that topical FK506 decreased the population of epidermis-infiltrating CD4+ T cells and suppressed the expression of CD54 and CD80 on I-A+ EC and LNC during hapten-induced contact hypersensitivity. Furthermore, topical FK506 profoundly impaired oxazolone-induced up-regulation of CD25 expression on CD4+ LNC and dramatically decreased hapten-induced expansion of I-A+/B220+ and I-A+/CD69+ LNC subsets. In conclusion, these results give new insights into the mechanisms of action of topical FK506 treatment.

Topical FK506 suppresses cytokine and costimulatory molecule expression in epidermal and local draining lymph node cells during primary skin immune responses

Recently, it has been shown that the immunosuppressive macrolide lactone, FK506, exerts good therapeutic efficacy in inflammatory skin diseases. The aim of this study was to analyze the influence of topical FK506 on molecular (IL-1alpha, IL-1beta, IL-2, IL-4, IL-12 p35, IL-12 p40, macrophage inflammatory protein-2 (MIP-2), granulocyte-macrophage CSF (GM-CSF), TNF-alpha, and IFN-gamma) and cellular (I-A+/CD80+, I-A+/CD54+, I-A+/CD69+, I-A+/B220+, and CD4+/CD25+) events in epidermal (EC) and local draining lymph node (LNC) cells during primary contact hypersensitivity responses. Cytokine mRNA levels for IL-1alpha, IL-1beta, GM-CSF, TNF-alpha, MIP-2, and IFN-gamma in EC and for IL-2, IL-4, IL-12 p35, IL-12 p40, and IFN-gamma in LNC were increased and resulted in significant LNC proliferation during oxazolone-induced contact hypersensitivity. Topical FK506 treatment dose-dependently suppressed oxazolone-induced LNC proliferation. This effect was correlated with decreased IL-1alpha, IL-1beta, GM-CSF, TNF-alpha, MIP-2, and IFN-gamma mRNA expression within the epidermis and decreased IL-12 p35 and p40 mRNA expression in LNC. Further analysis of the LNC cytokine pattern revealed that the production of both Thl (IFN-gamma and IL-2) and Th2 (IL-4) cytokines was dramatically impaired after topical FK506 treatment. Flow cytometric analysis showed that topical FK506 decreased the population of epidermis-infiltrating CD4+ T cells and suppressed the expression of CD54 and CD80 on I-A+ EC and LNC during hapten-induced contact hypersensitivity. Furthermore, topical FK506 profoundly impaired oxazolone-induced up-regulation of CD25 expression on CD4+ LNC and dramatically decreased hapten-induced expansion of I-A+/B220+ and I-A+/CD69+ LNC subsets. In conclusion, these results give new insights into the mechanisms of action of topical FK506 treatment.

The p68 autoantigen characteristic of rheumatoid arthritis is reactive with carbohydrate epitope specific autoantibodies

OBJECTIVE

The autoantigen p68 is a target of autoantibodies as well as autoreactive T cells with a high specificity in rheumatoid arthritis (RA). The binding characteristics of the autoantibodies to their antigen were now analysed biochemically and cytologically.

METHODS

Deglycosylation techniques as well as lectin and sugar competition experiments were performed to p68 to discover if the antibodies detected a glycoepitope, Its antigenicity was investigated applying anti-p68 antibodies derived from RA patients in comparison with polyclonal rabbit anti-p68 antibodies.

RESULTS

p68 specific antibodies from RA patients did not to bind to p68 that had been deglycosylated by alkaline beta-elimination, O-glycosidase or periodate treatment. In contrast, binding of p68 specific antibodies raised in rabbit was unaffected by either deglycosylation protocol. Furthermore, lectins specific for the carbohydrate N-acetylglucosamine competed with p68 specific antibodies from RA patients for antigen bindings. N-acetylglucosamine by itself also competed with patient derived anti-p68 antibodies for p68 binding. Again, rabbit and anti-p68 antibodies did not elicit these competitive effects. Applying cytoimmunofluorescence, p68 was present in the cytoplasm or endoplasmic reticulum and also in low abundance on the cell surface. Under heatshock conditions, p68 was detectable in the nucleus.

CONCLUSIONS

Autoimmunity to p68 during RA is carried by anti-carbohydrate autoantibodies. The carbohydrate modification of p68 appears to be N-acetylglucosamine, which may reflect the regulation of intracellular localisation of the antigen. It is hypothesised that a shift in glycosylation pattern accompanied by an unphysiological localisation of the antigen could trigger antigenicity of p68 during the pathogenesis of IRA.

A modified murine local lymph node assay for the differentiation of contact photoallergy from phototoxicity by analysis of cytokine expression in skin-draining lymph node cells

Since predictive differentiation of photoallergenic from phototoxic reactions, induced by low molecular weight compounds, represents a current problem, we tried to improve the differentiation between the two reactions by using a modified protocol of the local lymph node assay (LLNA). Briefly, groups of female BALB/c mice received compound solution or vehicle alone on the dorsum of both ears on 3 consecutive days. Immediately after compound application indicated groups of mice were exposed to a UVA light-dose of 10 J/cm2. Auricular lymph nodes draining the ear tissue were excised 24 h following the last exposure. Evaluation consisted of assessing lymph node weights and cell counts to monitor organ hyperplasia and in vivo-proliferative events following substance application. Furthermore, we analysed cytokine gene transcription in freshly prepared lymph node cells (LNC) and the cytokine release in vitro by restimulated CD4+ T-cells and antigen presenting cells (APC), both purified from the skin-draining lymph nodes. Both contact (photo) allergenic (oxazolone and tetrachlorosalicylanilide) and phototoxic substances (8-methoxypsoralen and acridine) caused a dose dependent increase in lymph node weights and cell counts pointing to an inflammatory process in the lymph nodes. Analysis of cytokine gene transcription ex vivo and cytokine release in vitro revealed that during the induction phase of contact (photo) allergy CD4+ T-cells produced IL-2 and IFN-gamma as well as IL-4 and IL-10, whereas IL-6 was derived from APC. In contrast, phototoxic reactions caused only an upregulation of IL-2 and IFN-gamma. Furthermore, we demonstrate that the release of IL-4 and IL-10 by CD4+ T-cells was clearly increased, whereas IL-6 and IFN-gamma expression was reduced or not changed following a challenge with contact (photo) allergens revealing an allergy-indicative shift in cytokine expression. In conclusion, our results show that contact photoallergenic reactions could be differentiated from phototoxic events by analysis of LNC cytokine expression patterns.

Testosterone-induced susceptibility to Plasmodium chabaudi malaria: persistence after withdrawal of testosterone

Testosterone induces susceptibility to Plasmodium chabaudi malaria by imposing restrictions on those mechanisms which mediate resistance controlled by genes of the H-2 complex and the non-H-2 background in mice. This study investigated whether these restrictions are abolished after withdrawal of testosterone. Female mice of the inbred strain C57BL/10 were treated with 0.9 mg testosterone twice a week for 3 weeks and testosterone was then withdrawn for 12 weeks. The treatment raised plasma testosterone levels from 0.18 ng/ml to 3.79 ng/ml. After the testosterone treatment, these levels progressively dropped and reached 0.21 ng/ml by week 12 after testosterone withdrawal. Surprisingly, however, the testosterone-induced susceptibility still persisted. When mice were challenged on week 12 after testosterone withdrawal, P. chabaudi infections were still fatal in testosterone-treated mice, in contrast to self-healing infections in resistant, i.e. untreated, control mice. In addition, testosterone caused a persistent decrease in the levels of total IgG antibodies, especially IgG1 and IgG2b isotypes. In contrast, testosterone-induced changes in spleen cells, such as the reduction in number by 50%, the relative increase in CD8+ cells and the decrease in Ig+ cells, as well as the acquisition of the susceptible phenotype, were completely reversed on week 10 after testosterone withdrawal at the latest. Testosterone did not affect the production of the TH1-signalling cytokine interferon-gamma and the TH2-signalling cytokines interleukin (IL)-4 and IL-10 in response to P. chabaudi malaria. Together, our data indicated that the gene-controlled host resistance to P. chabaudi malaria is subject to superior hormonal imprinting: when once induced by testosterone, mechanisms which suppress resistance thus causing susceptibility persist independently of testosterone.

A local lymph node assay to analyse immunosuppressive effects of topically applied drugs

Topical glucocorticosteroids represent the mainstay of antiinflammatory therapy in the treatment of inflammatory skin diseases. Their clinical use, however, is limited by local and systemic side-effects. Thus, in dermatopharmacology there is a large demand for alternative non-steroidal antiinflammatories. Other than transplantation models, most of the frequently used in vivo test systems for assessment of drug-induced immunosuppression measure changes in inflammatory skin responses by means of skin erythema and edema after challenge of sensitized animals. The aim of this study was to develop an alternative mouse model to detect and analyse immunosuppressive effects of topically applied drugs. On the basis of a modified local lymph node assay, we analysed effects of topical hydrocortisone, dexamethasone, mometasone furoate and FK506 (tacrolimus) during the induction phase of contact hypersensitivity. On 4 consecutive days, NMRI mice were treated on the dorsal surfaces of both ears with increasing concentrations of test compound. During the last 3 days, the mice received in addition the contact sensitizer, oxazolone (1%). On day 5, draining auricular lymph nodes were removed in order to assess lymph node cell counts and perform flow cytometric analysis of lymph node cell subpopulations (CD4+/CD25+, Ia+/CD69+, Ia+/B220+). All test compounds proved to exert significant immunosuppressive effects after topical application, but showed differences in their immunomodulatory potential. In conclusion, the local lymph node assay serves as an appropriate model to characterize immunosuppressive effects of topically applied drugs by measuring immunologically relevant end-points.

Murine lymph node antigen presenting cells are the main source of interleukin-6 in the initiation of delayed-type hypersensitivity

Interleukin-6 (IL-6) and Interferon gamma (IFN-gamma) production was analyzed in mice after topical exposure of the animals to Oxazolone, a well-known contact sensitizer. Since both IL-6 and IFN-gamma had been shown to be involved in the initiation of delayed-type hypersensitivity (DTH) reactions, and especially in contact sensitization (CS), we focussed our analysis on the cellular source of the two cytokines in local lymph nodes draining the site of exposure. We have demonstrated that IL-6 is found exclusively in lymph node antigen presenting cells (LNAPC), using three different approaches: i) in vitro restimulation of CD4-positive cells, obtained from Oxazolone-treated mice, in the presence of I-A-positive LNAPC, led to a strong IL-6 response, measured in culture supernatants by ELISA. Depletion of LNAPC in these suspensions prior to cultivation diminished IL-6 secretion, indicating that the LNAPC were the sole source of IL-6, ii) Staining of restimulated LNC for intracellular cytokines confirmed that LNAPC are the only source of IL-6 at various time-points during cultivation. iii) Competitive PCR analysis of cDNA, derived from freshly isolated lymph node cells (LNC) depleted either in CD8/B220- or CD8/B220/I-A-positive cells, showed that ex vivo IL-6-specific mRNA was found exclusively in the LNAPC. In contrast IFN-gamma is produced by CD4+ cells, although in some experiments CD8+ cells were also positive. Time-course analysis of the secretion of the two cytokines and their relation to lymphocyte blastosis in vitro showed that IL-6 peaked during the first 6 hrs of restimulation, whereas the number of IFN-gamma producing cells reached a maximum after 24 hrs and were closely correlated with the increasing number of in vitro blastocytes. Our data corroborate with other authors' investigations of DTH reactions, showing that IL-6, provided by LNAPC during primary responses in vivo, may serve as a co-stimulating factor for T cells.

Effect of topical cis-urocanic acid on local lymph node activation during contact sensitization in mouse, rat and guinea-pig

Cis-urocanic acid (cUCA) has been suggested as a mediator of impairment of contact hypersensitivity induction by ultraviolet B (UVB) irradiation. We ascertained whether topical cUCA influences local lymph node activation during induction of contact hypersensitivity. Topical cUCA or vehicle was applied during the local lymph node assay to oxazolone. Local lymph node weight and cell number were assessed in all animals. Additionally, cell proliferation rate was studied in Hartley guinea-pigs and CBA/Ca mice, whereas activation of antigen-presenting cells was quantified in NMRI mice and Wistar rats. Topical cUCA suppressed all parameters of local lymph node activation due to oxazolone application in guinea-pigs. No effect, with the exception of a suppression of antigen-presenting cell activity, was seen in mice. No effect was seen in rats. The study shows that topical cUCA may suppress local lymph node activation during contact sensitization and suggests that differences between the effect of cUCA in different animal species may exist.

Experiences with an advanced screening procedure for the identification of chemicals with an immunotoxic potential in routine toxicology

The development or selection of suitable tests for immunotoxicological screening and thus for incorporation into guidelines presents some problems. Most of the tests which have been proposed for immunotoxicological investigations and most knowledge and experience in immunology are based on mouse models. The standard species in the early phase of toxicological testing, however, is the rat. Any discussion about basic tests is hampered by a paucity of data from routine toxicological and/or epidemiological studies. Here we present data obtained from an advanced screening battery on the basis of OECD guideline 407. Thirteen pesticides of early development stage had been included in this screening. Two out of these 13 compounds turned out to be cytotoxic and were picked up by the immunological parameters as being 'primary immunotoxic', i.e., immunological changes not induced by overtly toxic doses ('indirect or secondary immunotoxic'). The advantages and disadvantages of each additional test is discussed as well as the comparison of the results obtained on the basic and the extended guideline test battery. In summary, the tests described here show that a little extra effort at the screening stage can save animals, time and costs for additional testing.

Pathology considerations for, and subsequent risk assessment of, chemicals identified as immunosuppressive in routine toxicology

Several proposals have been made with the aim of assisting in the early identification of chemicals with immunotoxic potential. The Organisation for Economic Cooperation and Development is now likely to incorporate enhanced immunopathology into the test guideline for the 28-day rat study, which may be regarded as a Tier I investigation. However, no guidelines have yet been proposed either for how the new data generated will be evaluated, or for how a subsequent risk assessment will be made. In this paper, considerations for the immunopathological assessment of the thymus, spleen, lymph nodes and bone marrow are described, together with comments on haematological and organ weight changes that may be associated with immunotoxicity. Their interpretation will depend on the doses at which changes are manifest, the quantity and quality of the effects observed and the presence and severity of other forms of toxicity. Lastly, risk assessment and the approach to Tier II testing in immunotoxicity is discussed. It is concluded that much of this work must be on a case-by-case basis, but should not in principle differ from the approach adopted for any other type of toxicity identified ina 28-day study.

Detection of photoreactivity demonstrated in a modified local lymph node assay in mice

Photoallergic and phototoxic reactions are an increasing problem in dermatologic practice. Currently available test models are heterogeneous and do not allow differentiation between photoallergic and phototoxic reactions. We have modified the local lymph node assay to screen for photoreactive compounds. We found an ultraviolet A (UVA) irradiation-dependent increase in the weights and cell counts of the auricular lymph nodes after application of 8-methoxypsoralen, tribromosalicylanilide, trichlorosalicylanilide, chlorpromazine and promethazine. In contrast to these photoreactive compounds, contact sensitizers did not produce any reaction to UVA irradiation in the local lymph node assay. This assay system has the advantage of being less expensive and less time-consuming and might even be able to differentiate between phototoxic, photoallergic and contact allergic reactions.

The identification of chemicals with sensitizing or immunosuppressive properties in routine toxicology

In the context of this paper, immunotoxicity is taken to encompass immunosuppression/immunopotentiation and allergy. Over the last 10 to 15 years, well characterized methods for the assessment of altered immune competence have been reported. This has led to proposals for tiered testing schemes. This review examines the suitability of immunotoxicity parameters for inclusion in routine 28-day studies and comments on methods that have been proposed for incorporation within the guidelines issued by the US FDA and US EPA and OECD. It is recommended that the existing OECD Guideline 407 is modified to incorporate total and differential blood cell counts, spleen and thymus weight and histopathology, and draining and distal lymph node histopathology for Tier I level testing. Data so generated will provide a reliable and accurate means of identifying at an early stage potential immunotoxic effects. Tier II testing should be carried out on a case by case basis and only assuming positive results are obtained at Tier I. An increasingly sophisticated understanding of the nature of immune responses to chemical allergens has facilitated the design of novel predictive methods for the identification of sensitizing activity. Opportunities which arise from these new developments in allergy testing such as the local lymph node assay, mouse ear swelling test, and the mouse IgE test should be monitored closely.

IL-4 is required for the IgE and IgG1 increase and IgG1 autoantibody formation in mice treated with mercuric chloride

Previous studies have established that in susceptible mouse strains, such as A.SW (H-2s), repeated injections of subtoxic doses of HgCl2 induce increased serum levels of total IgE and IgG1, high serum titers of antinuclear autoantibodies (ANo1A), and immune-complex glomerulonephritis. Moreover, it has been shown that susceptibility is determined by H-2As and that Th cells are required for the induction of these immunopathologic alterations by HgCl2. In the present study we showed that treatment in vivo with anti-IL-4 mAb completely abrogated the HgCl2-induced increase in total IgE and partially inhibited the increase in IgG1, but failed to suppress the increase in IgG2A. Furthermore, we showed that IL-4 influences the pattern of IgG subclass distribution among ANo1A of HgCl2-treated mice. Whereas treatment with anti-IL-4 mAb significantly reduced the titers of IgG1 ANolA, it increased those of IgG2A, IgG2B, and IgG3 ANolA. Thus, these results show that IL-4 contributes to the optimal formation in vivo of murine IgG1 and that it is involved in the autoantibody formation of a systemic autoimmune disease. The available evidence suggests that HgCl2 induces an increased production of IL-4 by Th2 cells. If this is correct, it implies that MHC class II alleles determine whether the preferential response to HgCl2 is made by Th1 or Th2 cells and, hence, the type of immunopathologic alterations ensuing.

IL-4 is required for the IgE and IgG1 increase and IgG1 autoantibody formation in mice treated with mercuric chloride

Previous studies have established that in susceptible mouse strains, such as A.SW (H-2s), repeated injections of subtoxic doses of HgCl2 induce increased serum levels of total IgE and IgG1, high serum titers of antinuclear autoantibodies (ANo1A), and immune-complex glomerulonephritis. Moreover, it has been shown that susceptibility is determined by H-2As and that Th cells are required for the induction of these immunopathologic alterations by HgCl2. In the present study we showed that treatment in vivo with anti-IL-4 mAb completely abrogated the HgCl2-induced increase in total IgE and partially inhibited the increase in IgG1, but failed to suppress the increase in IgG2A. Furthermore, we showed that IL-4 influences the pattern of IgG subclass distribution among ANo1A of HgCl2-treated mice. Whereas treatment with anti-IL-4 mAb significantly reduced the titers of IgG1 ANolA, it increased those of IgG2A, IgG2B, and IgG3 ANolA. Thus, these results show that IL-4 contributes to the optimal formation in vivo of murine IgG1 and that it is involved in the autoantibody formation of a systemic autoimmune disease. The available evidence suggests that HgCl2 induces an increased production of IL-4 by Th2 cells. If this is correct, it implies that MHC class II alleles determine whether the preferential response to HgCl2 is made by Th1 or Th2 cells and, hence, the type of immunopathologic alterations ensuing.

Mercuric chloride induces autoantibodies against U3 small nuclear ribonucleoprotein in susceptible mice

Autoantibodies to nucleolar components are a common serological feature of patients suffering from scleroderma, a collagen vascular autoimmune disease. While animal models, which spontaneously develop abundant anti-nucleolar antibodies, have not yet been described, high titers of such antibodies may be induced by treating susceptible strains of mice with mercuric chloride. We have identified the nucleolar autoantigen against which the HgCl2-induced IgG autoantibodies from mice of strain B10.S are directed. It is a protein with an apparent molecular mass of 36 kDa and a pI value of approximately 8.6, which is associated with the nucleolar small nuclear RNA U3, and by these criteria must be identical with a polypeptide called fibrillarin. It is striking that scleroderma patients spontaneously produce autoantibodies against the same U3 ribonucleoprotein (RNP). The HgCl2-induced murine and the scleroderma-specific human anti-U3 RNP autoantibodies were indistinguishable in their reactivities toward fibrillarin. They further resemble each other insofar as both recognize epitopes on the 36-kDa protein, which have been highly conserved throughout evolution. Our results provide a basis to investigate at the molecular level whether similar immunoregulatory dysfunctions may lead to the preferential anti-U3 RNP autoantibody production in the animal model and in scleroderma patients.

Identification of inhibitory growth factors from a N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide-induced murine bladder cancer cell line

The N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT)-induced murine bladder carcinoma cell line MBT-683 contains growth-stimulating (TGF) and growth-inhibiting factors (GI). These activities coeluted on BioGel P-30 between molecular weights 6,000 and 29,000 daltons. They can be separated by high performance liquid chromatography. Both activities were destroyed by trypsin and dithiothreitol. However, they were resistant to acid and heat. Pool 1 (TGF) stimulated the growth of normal rat kidney cells, whereas pool 2 (GI) inhibited the colony formation of the cell lines MBT-683 and RBTCC-8.

Induction of proliferative and cytotoxic responses in resting Lyt-2+ T cells with lectin and recombinant interleukin 2

The lectin leucoagglutinin has been used to induce reactivity to interleukin 2 (IL2) in unseparated spleen cells and in highly purified Lyt-2+ lymph node T cells. Recombinant human IL2 and various other IL2-containing preparations, including concanavalin A-induced spleen cell supernatant, were compared for their capacity to support DNA synthesis and cytotoxic activity. In contrast to published reports, we found that the capacity of all preparations tested was identical in both functional assays, if they were adjusted to the same IL2 titer. Our inability to detect a requirement for an externally added cytotoxic T cell differentiation factor could either mean that IL2 is sufficient for the promotion of both proliferation and differentiation in leucoagglutinin-activated resting cytotoxic T cell precursors, or that under our experimental conditions, T cell differentiation factor is endogenously produced by Lyt-2+ T cells.

Somatic H-2Kk variants reveal nonidentity of serological and cytotoxic T cell-defined Kk determinants

The relationship of serologically defined determinants to determinants recognized by cytotoxic T cells on molecules encoded by the Kk gene of the murine major histocompatibility complex (H-2) has been analyzed. For this purpose we used three somatic variants of a Kk-expressing lymphoma line lacking individual determinants of the Kk molecule, as defined by monoclonal antibodies (mAb), as target cells for Kk-specific alloreactive and Kk-restricted cytotoxic T lymphocytes (CTL) cloned by limiting dilution. Neither alloreactive nor fluorescein isothiocyanate, influenza- or Newcastle disease virus-specific Kk-restricted CTL clones were found to distinguish between variants and wild type cells, indicating that the serologically defined determinants lost by the variants were not essential for antigen recognition of CTL with these specificities. On the other hand, two of the variants lacking either one of a pair of serological determinants were discriminated from Kk wild type cells by about 40% of Kk-restricted, trinitrophenol (TNP)-specific CTL clones. The third variant, lacking both of the determinants, however, was lysed by all CTL clones to the same extent as wild type cells. From these results we conclude that the determinants restricting the TNP-specific CTL were also not identical with those defined by mAb. In experiments performed to optimize the conditions for the limiting dilution analysis we found that the specificity of the CTL stimulation was strongly dependent on the concentration of T cell growth factor (interleukin 2) in the cultures during CTL stimulation. High concentrations of IL2 resulted in a drastic increase in the frequency of CTL clones. Part of these clones, however, were found not to be specific for antigens present on the stimulator cells.