Activation of CD4+ and CD8+ lymphocyte subsets by streptozotocin in murine popliteal lymph node (PLN) test

Popliteal lymph node assay: facts and perspectives

The popliteal lymph node assay (PLNA) derives from the hypothesis that some supposedly immune-mediated adverse effects induced by certain pharmaceuticals involve a mechanism resembling a graft-versus-host reaction. The injection of many but not all of these compounds into the footpad of mice or rats produces an increase in the weight and/or cellularity of the popliteal lymph node in the treated limb (direct PLNA). Some of the compounds known to cause these adverse effects in humans, however, failed to induce a positive PLNA response, leading to refinements of the technique to include pretreatment with enzyme inducers, depletion of CD4(+) T cells or additional endpoints such as histological examination, lymphocyte subset analysis and cytokine fingerprinting. Alternative approaches have been used to improve further the predictability of the assay. In the secondary PLNA, the test compound is injected twice in order to illicit a greater secondary response, thus suggesting a memory-specific T cell response. In the adoptive PLNA, popliteal lymph node cells from treated mice are injected into the footpad of naive mice; a marked response to a subsequent footpad challenge demonstrates the involvement of T cells. Finally, the reporter antigens TNP-Ficoll and TNP-ovalbumin are used to differentiate compounds that induce responses involving neo-antigen help or co-stimulatory signals (modified PLNA). The PLNA is increasingly considered as a tool for detection of the potential to induce both sensitization and autoimmune reactions. A major current limitation is validation. A small inter-laboratory validation study of the direct PLNA found consistent results. No such study has been performed using an alternative protocol. Other issues include selection of the optimal protocol for an improved prediction of sensitization vs autoimmunity, and the elimination of false-positive responses due to primary irritation. Finally, a better understanding of underlying mechanisms is essential to determine the most relevant endpoints. The confusion resulting from use of the PLNA to predict autoimmune-like reactions as well as sensitization should be clarified. Interestingly, most drugs that were positive in the direct PLNA are also known to cause drug hypersensitivity syndrome in treated patients. This observation is expected to open new avenues of research.

The Reactive d-Glucopyranose Moiety of Streptozotocin Is Responsible for Activation of Macrophages and Subsequent Stimulation of CD8+ T Cells

The antitumor drug streptozotocin (STZ) is commonly used as a diabetogenic compound in animal models. At relatively low doses, STZ-induced beta cell destruction is associated with Th1-driven type 1 immune reactions, including macrophages (MPhi) and IFN-gamma-producing CD8(+) T cells. STZ induces similar Th1-dependent effects in the popliteal lymph node assay (PLNA), and because this assay allows straightforward examination of early immunostimulating processes, the PLNA was used to further examine the importance of MPhi and structural properties of STZ in relation to the induction of type 1 immune responses. Results show that elimination of MPhi with clodronate-containing liposomes prior to exposure to STZ prevents the occurrence of some (CD8(+) T cell activation, IFN-gamma production, and tissue destruction) but not all (IgG2a formation) type 1 immune responses. It appeared that stimulation of MPhi depends on the d-glucopyranose moiety of STZ, as well as on the intact reactive N-methyl-N-nitrosourea (MNU) moiety. However, the MNU moiety suffices to induce IgG2a formation. In addition, STZ-derived nitric oxide may have modulating effects on the elicitation of STZ-induced immune responses. Present results support the idea that MPhi activation is indispensable for the STZ-induced tissue destructive type 1 responses and that various STZ-induced type 1 immune responses are differently regulated.

Cytokine release does not improve the sensitivity and specificity of the direct popliteal lymph node assay

The popliteal lymph node assay (PLNA) is being considered as a tool to predict the potential of drugs for inducing systemic autoimmune and hypersensitivity reactions. Despite the use of different technical approaches and the evaluation of over 130 compounds, the sensitivity and specificity of the PLNA are still debatable due to many false positive and negative responses. In this study, cytokine production was assessed as a possible endpoint to improve the direct (primary) PLNA. Diclofenac, imipramine, hydralazine, glafenin and minocycline were tested using the classical procedure. TH1 cytokines (IL-2 and IFN-gamma), TH2 cytokines (IL-4 and IL-5) and pro-inflammatory cytokines (IL-6, TNF-alpha, monocyte chemoattractant protein-1 (MCP-1), IL-12p70 and IL-10) were measured in the serum and in suspensions of popliteal lymph node cells of female Balb/c mice by flow cytometry 7 days after drug administration. Only diclofenac and imipramine induced a cellularity index above 5 (considered as a positive response). Of the five tested drugs, only diclofenac induced a slight increase in TH1 cytokines, but there were no effects on TH2 cytokine production whatever the drug tested. Diclofenac increased the production of pro-inflammatory cytokines, whereas the production of MCP-1 was increased by minocycline and decreased by imipramine. No changes in serum cytokine levels were evident. These results suggest that measuring cytokine release is unlikely to improve the sensitivity and specificity of the direct PLNA.

Popliteal lymph node responses to acetone and ethanol differ from those induced by streptozotocin

The popliteal lymph node (PLN) assay was proposed to detect the potential of immunotoxicants for inducing systemic autoimmune-like reactions, but also xenobiotics that are sensitizing or exert immunostimulatory properties. Results on over 100 chemicals, mostly pharmaceuticals, are available with the PLN assay and show many correlations between rodent data and the clinical experience. A major issue is that the mechanisms involved have not been fully elucidated. In order to provide mechanistic clues to improve the predictability of the PLN assay, the effects of streptozotocin (STZ) were compared to those of ethanol and acetone in normal C57Bl/6 mice as well as mice depleted in CD4+ or CD8+ T-cells by treatment with specific monoclonal antibodies. STZ, ethanol and acetone gave similar positive responses in normal mice. Neither CD4+ nor CD8+ T-cell depletion influenced the PLN responses to ethanol or acetone, whereas CD8+ in contrast to CD4+ T-cell depletion abolished the response to STZ. There was an increase in the production of IL-6 and IFN-gamma mRNAs measured by RT-PCR in STZ-, but not in ethanol- or acetone-treated normal mice. The production of TNFalpha, IL-1alpha, IL-1beta, IL-2R and IL-12 mRNAs was increased whatever the treatment, but increases were 2- to 3-fold greater after STZ than ethanol or acetone. These results suggest that PLN responses to primary irritants such as ethanol and acetone essentially reflect non-specific inflammation, whereas PLN responses to an autoimmunogenic compound such as STZ involve CD8+ T lymphocytes and the production of IFN-gamma and IL-6. These findings may prove useful to improve the predictability of the PLN assay.

Tritiated thymidine incorporation does not enhance sensitivity of the popliteal lymph node assay

The popliteal lymph node (PLN) assay has been proposed as a tool to predict drugs and chemicals with the potential to induce systemic autoimmune reactions in man. In this assay, weight and cellularity indices typically are the measured endpoints. The present study was conducted to test whether incorporation of tritiated thymidine could improve sensitivity of the PLN assay. Male and female Balb/c mice were injected with 20 microCi of [3H]-methyl-thymidine intravenously 7 days after receiving 0.5, 1 or 2 mg of diphenylhydantoin, streptozotocin, sulfamethoxazole, ofloxacin, phenobarbital, or metformin intradermally. Results obtained with incorporation of tritiated thymidine were compared to weight indices. No consistent or marked differences in these endpoints were noted whatever the compound used. This study shows that incorporation of tritiated thymidine does not improve sensitivity of the PLN assay.

Application of the popliteal lymph node assay in immunotoxicity testing: complementation of the direct popliteal lymph node assay with flow cytometric analyses

The popliteal lymph node assay (PLNA) has been proposed to measure the immunosensitizing potential of chemicals. The direct PLNA detects an immunomodulating effect but does not give insight into the mode of action of the chemical under test. Modifications of this test have been proposed, but they are difficult to perform in routine toxicity testing and require many animals. In the present investigation the direct PLNA was extended with the flow cytometric determinations of: (a) lymphoblasts; (b) the phenotyping of lymphoid subpopulations; (c) the determination of expression of proliferation/activation markers CD25, CD69 and CD62L/CD44 and (d) the analysis of intracellular cytokines interferon gamma, interleukin 2 and interleukin 4. Streptozotocin, hydrazine, HgCl2 and trinitrobenzene sulfonic acid were used as model chemicals. The different mode of action of these substances was well documented by the techniques applied. As the proposed flow cytometric methods can easily be performed and do not require additional test animals this complementation of the direct PLNA seems a promising approach in immunotoxicity testing.

The local lymph node assay and potential application to the identification of drug allergens

The local lymph node assay (LLNA) is a method for the identification of skin sensitization hazard. The method is based upon measurement of proliferative responses induced in draining lymph nodes following topical exposure of mice to the test chemical. More recently the LLNA has also been used for the evaluation of relative skin sensitization potency in the context of risk assessment. Idiosyncratic drug reactions resulting from the stimulation of allergic or autoimmunogenic responses are poorly understood but represent an important clinical problem. In this article, the potential utility of the LLNA, either in a conventional modified configuration, to provide information of value in assessment the potential for systemic allergenicity is considered.

Increased production of interferon-gamma, but not IL-4 mRNA, by streptozotocin in the popliteal lymph node assay

The popliteal lymph node (PLN) assay has been proposed as a tool to predict systemic autoimmune reactions induced by medicinal products and chemicals, the mechanisms of which are poorly understood. To determine whether PLN responses involved Th1 or Th2 cell control, or both, the effects of streptozotocin (STZ), a prototypic immunotoxic compound, were analysed on the production of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) mRNA by lymph node cells after injection into the hind footpad of C57 BL/6 mice. Streptozotocin induced a dramatic increase in IFN-gamma mRNA production, which correlated with PLN responses as evidenced by augmented weight and cellularity indices. No effect on IL-4 mRNA synthesis was noted. These results suggest that a Th1 response is involved in the PLN response to STZ.

The popliteal lymph node response to streptozotocin is under type 1, MHC class-I restricted, CD8(+) T-cell control

The popliteal lymph node (PLN) assay has been proposed to predict the 'autoimmunogenic' potential of xenobiotics. A better understanding of the processes involved in PLN responses is needed to establish the value of this assay for preclinical safety evaluation. In order to determine whether PLN responses involve CD4(+) or CD8(+) T-cells, the effects of streptozotocin (STZ), a prototypic immunotoxic compound, were analyzed after injection into the hind footpad of C57 BL/6 mice and major histocompatibility complex (MHC) class I or II deficient mice. The involvement of type 1 or type 2 cell control on the production of cytokine mRNAs was analyzed in lymph node cells by quantitative RT-PCR, together with the analysis of a wide range of cytokine mRNAs after STZ injection (IL-1alpha, IL-1beta, TNF-alpha, IFN-gamma, IL-2, IL-2 receptor, IL-4, IL-5, IL-6, IL-10 and IL-12). We have found that mice depleted in CD8(+) T-cells did not respond to STZ, whereas mice depleted in CD4(+) T-cells exhibited the expected positive PLN responses, with increased weight and cellularity indices. STZ induced a low production of interleukin (IL)-2 mRNAs, a mild increase in IL-1alpha and IL-6 mRNAs production, and a dramatic increase in IFN-gamma, IL-1beta, TNF-alpha, IL-12 and IL-2 receptor mRNAs, which correlated with positive PLN responses. No effects on IL-4, IL-5 and IL-10 mRNAs synthesis were noted. In CD8(+) T-cell deficient mice, there was no production of IFN-gamma or IL-6 mRNAs. These results suggest that PLN responses to STZ are under the control of type 1, MHC class-I-restricted, CD8(+) T-cells. This is in accordance to the known physiopathology of STZ-induced diabetes. Additional studies are necessary to establish the mechanism of CD8+ T-cell activation.

Selective immunomodulation by the autoimmunity-inducing xenobiotics streptozotocin and HgCl2

Exposure to certain drugs and environmental chemicals can provoke the onset of autoimmune disease in susceptible individuals by releasing (self) epitopes for which tolerance has not been established, while simultaneously providing the necessary adjuvant activity. The resulting response type is influenced by the genotype of exposed individuals and relates to susceptibility to the adverse immune effects of the chemicals. Here, we assessed the modulatory role of the chemical compounds themselves. A single injection of streptozotocin (STZ) increased the number of CD8+ cells, macrophages, apoptotic cells, and IFN-gamma-producing T helper and T cytotoxic cells, whereas the number of CD4+ cells and B cells was reduced in the draining lymph node. Coinjection with the reporter antigen TNP-OVA resulted in primary and secondary production of TNP-specific antibodies that were predominantly of IgG2a and IgG2b isotype, whereas STZ did not enhance priming for delayed-type hypersensitivity (DTH) responses to TNP-OVA. Injection of HgCl2 on the other hand, reduced the number of IFN-gamma-producing cells, induced accumulation of B cells and CD4+ and CD8+ T cells, enhanced IgG1 and IgE production to TNP-OVA, and primed for secondary IgG1 and IgE production as well as for DTH reactions. Together these results indicate that a single injection of STZ stimulates type-1 responses, whereas HgCl2 enhanced mixed type-1 and -2 responses in BALB/c mice. These response types match the (auto)immune effects elicited to unknown (auto)antigens following multiple injections of these chemicals.

In vitro lymphotoxicity and selective T cell immunotoxicity of high doses of acyclovir and its derivatives in mice

The antiviral drug acyclovir [9-(2-hydroxyethoxymethyl)guanine (ACV)], its 7-isomer (7-ACV) and its two derivatives: N2-acetyl ACV (ac-ACV) and N2,O-diacetyl ACV (diac-ACV) were examined for their potential in vitro lymphotoxicity and in vivo immunotoxicity in mice. In vitro lymphotoxicity of ACV and its acetylated derivatives was low, whereas the 7-ACV isomer enhanced the in vitro cell proliferation in PHA-stimulated cultures. Addition of 2'-deoxyguanosine (dGuo) did not exhibit any inhibitory potential of ACV. However, reduction in the absolute number of CD3+, CD8+, and CD25+ cells, but not Ig+ cells, was noted at high concentrations of ACV and its derivatives, suggesting a selective T cell cytotoxicity. Similarly, the in vivo exposure revealed selective T cell immunotoxicity of ACV and its derivatives since the reduced number of Thy 1.2+ and CD8+ cells was not accompanied with any marked changes in the Ig+ population. The CD4+/CD8+ ratio was affected both in vitro and in vivo by high concentrations of ACV.

Streptozotocin: inherent but not expressed skin sensitizing activity

We have shown previously that the alkylating agent streptozotocin (STZ) fails to induce responses in the murine local lymph node assay, a predictive test for contact sensitizing potential. In the present study, we demonstrate that this same compound when injected intradermally into the ears of mice provokes a dose-dependent induction of draining lymph node cell proliferation. These data indicate that the intrinsic immunogenicity of STZ is not displayed in the local lymph node assay under conditions of conventional topical exposure, secondary to a failure to cross the lipophilic stratum corneum in sufficient quantities. This finding has implications for the discernment of structure-activity relationships in contact sensitization.

Immunoactivating potential of multilamellar liposome vesicles (MLV) in murine popliteal lymph node (PLN) test

Immunoactivating properties of subcutaneously injected small unilamellar vesicles (SUV) and multilamellar liposome vesicles (MLV) were studied in relation to different transition temperatures (Tc) of phospholipids. Liposome-induced proliferative reaction in the popliteal lymph node (PLN) was quantified by subsequent cytometric assay. Early cell activation during the onset of PLN reaction was monitored by immunophenotyping of lymphocyte subsets stained with a panel of monoclonal antibodies (mAbs) and gating the subset-specific large/activated cells. Injection of MLV liposomes containing distearoyl phosphatidylcholine (DSPC) and dipalmityl phosphatidylcholine (DPPC), characterized by relatively high Tc, resulted in a marked PLN reaction, increased numbers of CD4+, CD8+, Ig+ subsets and increased proportions of large/activated EAM+ (CD69+) and CD25+ (IL-2 receptor+) cells. The reaction was dose and time dependent. In contrast, injection of MLV liposomes containing lipids of low Tc, such as egg phosphatidylcholine (egg PC) and dimyristoyl phosphatidylcholine (DMPC), did not show any immunoactivation. In addition, there was a highly reduced immunoactivating potential of small-size SUV liposomes over large-sized MLV of identical phospholipid composition. Generally, both lipid composition and vesicle size appeared to be essential for the immunoactivating potential of liposomes. The data suggest a possible correlation between the Tc of the phospholipid and the immunoactivating potential of the large-sized MLV liposomes.

Decreased interleukin-2 receptor and cell cycle changes in murine lymphocytes exposed in vitro to low doses of cadmium chloride

Relationships between in vitro cadmium-related cell cytotoxicity, ultrastructural changes and altered cell cycle were determined at 21-72 h after mitogenic stimulation of C57BL/6 mouse spleen lymphocytes with concanavalin A (Con A). Relatively low doses, 0.6-10 microM cadmium (Cd), added at 4 h after the mitogen activation, induced a significant cell cytotoxicity and reduced the lymphoblastic activity of the cells. Cytometric analysis of the lymphoid cell cycle at 72 h revealed that at concentrations > or = 0.6 microM Cd, the number of cells arrested in G0 + G1 phase increased, whereas the proportions of cells of the S and G2 + M phases were substantially reduced. Staining of cells with fluorescent anti-CD25 monoclonal antibody showed a cadmium-related decreased number and relative mean fluorescence of CD25+ cells, demonstrating a decreased level of interleukin-2 receptor (IL-2R). Furthermore, immunogold ultramicroscopic assay was developed for determination of intracellular interleukin-2 (IL-2) in cadmium-treated lymphocytes. The level of cytoplasmic and nuclear IL-2, localized in situ by colloidal gold ultraimmunocytochemical technique, has been estimated as markedly decreased in cells treated with > or = 1.2 microM Cd, as compared with the untreated controls. Disorganization/fragmentation of mitochondrion cristae and dilatation of cisternae of the Golgi apparatus appeared as the major ultrastructural change in 1.2 microM Cd-treated lymphocytes. Interestingly, addition of cadmium in the incubation medium, up to 4 h after mitogen activation, also interacted with lymphoproliferative mechanisms of cells in G0 + G1, S and G2 + M phase. Overall, multiple ultrastructural changes of Cd-treated lymphoid cells were clearly related with the reduced cell viability and reduced number of activated lymphoblasts.

Different T-cell activation by streptozotocin and Freund's adjuvant in popliteal lymph node (PLN)

A popliteal lymph node (PLN) test was further validated for predictive screening of autoimmunity-inducing drugs. Autoimmune-like T-cell activation of streptozotocin (STZ) was compared with the effect of Freund's complete adjuvant (FCA), injected locally into the foot pad of BALB/c mice. Early cell activation in enlarged PLN was monitored by flow cytometry. Injection of both STZ and FCA markedly increased the absolute PLN cell number as well as specific T-helper (CD4+), T-suppressor/cytotoxic (CD8+), and B (Ig+) subsets. However, quantitative analysis of early T-cell activation revealed important differences between STZ-induced PLN reaction and FCA-related lymphoproliferation. At 72 h, the number of cells stained with anti-early activation marker (EAM+; CD69+) increased over 10 times in STZ-enlarged nodes and only 3 times in the FCA-inflamed nodes. Furthermore, different cytometric profiles were noted for STZ-activated and FCA-activated cells stained with anti-interleukin-2 receptor (IL-2R) (CD25+). The data suggest the applicability of early cytometric screening of enlarged PLN for predictive analysis detection of chemicals inducing an autoimmune-like reaction.

Predictive immunotoxicological test systems: suitability of the popliteal lymph node assay in mice and rats

This article reviews results obtained with popliteal lymph node assays (PLNAs) in rodents and discusses their ability to detect and analyze immunotoxic effects of drugs and other low molecular weight (LMW) chemicals. In its basic form, the PLNA measures activation of the draining lymph node of the hind paw (i.e., the PLN) after injection of a test chemical into the hind foot pad. The assay appears to be appropriate to recognize sensitizing, that is, allergenic and autoimmunogenic, chemicals, as well as nonsensitizing immunostimulatory chemicals. With modifications, PLNAs can detect immunosuppressive chemicals and distinguish sensitizing from nonsensitizing chemicals. Furthermore, modified PLNAs enable detection of known as well as unknown sensitizing metabolites, and may assist in the identification of the self-molecules that act as carriers for chemical sensitization or as targets of chemical-induced autoimmune disease. Experience with PLNAs shows that they are rapid, reproducible, and objective tests for recognition of sensitizing or otherwise immunomodulating chemicals. Because current protocols of toxicity testing are insensitive in predicting a chemical's potential to result in immunomodulation, PLNAs, when further validated, may provide welcome supplements to routine toxicity screening of chemicals, thus enhancing chemical safety.

Modulation of exercise-induced immunosuppression by dietary polyunsaturated fatty acids in mice

The possible interaction between intense exercise, known to suppress the immune response, and nutritive factors, such as polyunsaturated fatty acids (PUFA), was examined in inbred female C57Bl/6 mice. The animals received for 8 wk either a natural ingredient diet or a diet supplemented with 10 g/100 g linseed oil containing over 50% of 18:3 (n-3) alpha-linoleic acid. Other groups received PUFA containing only traces of 18:3 (n-3) fatty acid; beef tallow, containing mostly 18:1 (n-9) saturated fat, safflower oil, an 18:2 (n-6) PUFA, and fish oil, containing longer chain (n-3) PUFA. Each dietary group was divided into two subgroups: sedentary diet controls and exercised animals. Exercise consisted of continuous swimming at high intensity until exhaustion. It was shown in three separate experiments that (1) the primary humoral response to sheep red blood cells, determined by the plaque-forming cell (PFC) assay, was affected by PUFA diet in sedentary animals in the order beef tallow > control diet > safflower oil > fish oil > linseed oil, and (2) the PFC response was suppressed by the exhaustive exercise, as compared to sedentary controls, except for animals fed 18:3 (n-3) linseed oil, where the normal response was noted. Phagocytosis of fluorescent microspheres by peritoneal macrophages, determined by flow cytometry, was significantly lower in exercised animals receiving the linseed oil diet, whereas other diets either increased or did not significantly change the macrophage phagocytic activity, compared to the sedentary diet controls. Spleen lymphocyte subsets were unchanged in exercised animals except for a marked shift from the lymphoid peak toward the erythroid peak. Generally, our data showed a marked immunomodulatory effect of 18-3 (n-3) alpha-linoleic acid on the exhaustive exercise-related immunosuppression, as compared to the effects of other selected PUFA.

Lymphocyte activation by liposome-trapped streptozotocin in murine popliteal lymph node (PLN) test

The lymphoproliferative potential of liposome-trapped streptoztocin (STZ) was compared to the effect of saline-dissolved STZ injected locally into the foot pad of CD-1 mice. Popliteal lymph node (PLN) enlargement and early cell activation of lymphocyte subsets were monitored during the onset of STZ-induced autoimmune-like reaction. Injection of the optimal STZ dose, 0.5 mg/foot pad, markedly increased the absolute PLN cell number as well as specific T-helper (CD4+), T-suppressor/cytotoxic (CD8+), and B-(Ig+) cell subsets stained with fluorescent monoclonal antibodies. Furthermore, there was a marked increase in the number of large/activated CD4+ and CD8+ cells and subsets bearing specific markers of early activation. These included cells stained with fluorescein-conjugated monoclonal antibodies against interleukin-2 receptor (CD25+) and early activation marker (EAM+) (CD69+), and with fluorescein-conjugated peanut agglutinin (PNA+). Surprisingly, the injection of liposome-trapped STZ, at a 1/10 of the optimal dose only, induced a marked PLN enlargement comparable to the effect of optimal STZ dose. The effect of liposome-STZ could be dissociated from the non-drug-containing MLV-related lymphocyte activation. The data suggest several possible advantages from the introduction of chemicals by the liposome route and the subsequent PLN test for chemical-induced autoimmunity. Toxicological advantages could involve better control of chemical exposure, controlled exposure to the water-insoluble substances, drastic reduction of xenobiotic dose, a stronger, clear PLN response and possible elimination or at least restriction of false-negative results, due to the liposome adjuvancity. Overall, application of liposomes as an exposure route potentialized the STZ-induced early lymphocyte activation.

Comparison of popliteal lymph node responses in various strains of rats

Outbred (namely Wistar and Sprague-Dawley) and inbred (Wistar-Furth, Lewis, Fisher 344 and Brown-Norway) strains of rats were screened for their responses to reference compounds in the popliteal lymph node (PLN) assay. Streptozotocin and diphenylhydantoin gave positive responses as evidenced by increased weight and cellularity indices in all strains used whereas procainamide, isoniazid and barbital consistently gave negative responses. Although these findings overall are in agreement with previous investigations involving these compounds, the lack of marked interstrain differences in PLN responses argues against a strong immunogenetically controlled mechanism as could be assumed in presumably auto-immune reactions. The question is raised whether drug-induced side-effects predicted by the PLN assay are basically non-autoimmune as suggested by clinical and immunological findings in man.

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.

Morphology of popliteal lymph node responses in Brown-Norway rats

The popliteal lymph node (PLN) assay has been proposed as a tool to predict in rodents those xenobiotics likely to induce autoimmune reactions in humans. To further validate this assay and to study the mechanisms involved, histologic changes in PLNs from rats injected with streptozotocin, diphenylhydantoin, pure acetone, or 50% ethanol were compared to a local graft-versus-host (GvH) reaction. This study suggests that routine histology of PLNs is instrumental to discard primary irritants. In addition, the hypothesis of a GvH-like mechanism in positive PLN responses is supported by the finding that the reference compounds streptozotocin and diphenylhydantoin produced histologic changes similar to a "true" local GvH reaction.

Cytometric profiles of bone marrow and spleen lymphoid cells after mercury exposure in mice

The potential immunotoxic effects of mercury chloride on murine bone marrow (bm) cell subpopulations, including analysis of maturation patterns for B-cells, were evaluated by flow cytometric analysis. CD-1 outbred mice were exposed for 28 days to relatively low doses of 25-100 ppm HgCl2 in drinking water and the mercury-related functional cellular changes were validated in a macrophage phagocytosis assay. Lymphocyte subsets from the bone marrow population were stained with PNA lectin and a panel of monoclonal antibodies against cell surface antigens. The incidence of subset-specific staining was also monitored in spleens and thymuses. A dose-effect correlation was noted for the mercury-related activation of macrophage phagocytosis. Subchronic exposure to mercuric chloride resulted in a transient (7-14 day) decrease of the lymphoid/total bm cell ratio and affected the incidence of splenic T-cell subsets, however, without a clear dose-response correlation. The B-cell population in spleen and maturation patterns of B-cells in bm appeared to be unaffected by the mercury exposure. Overall, cytometric analysis of lymphoid cell subsets in murine bone marrow revealed transient and subset-non-specific cell fluctuations after subchronic exposure to inorganic mercury.

The popliteal lymph node assay: a tool for studying the mechanisms of drug-induced autoimmune disorders

Whereas it is still impossible to predict the risk for organ-specific drug-induced autoimmune disorders in animals, a large body of evidence suggests that the popliteal lymph node assay (PLNA) in mice or rats is instrumental to predict systemic drug-induced autoimmune disorders. Metabolites may be involved instead of the parent molecules in a few instances as shown by studies using animals pretreated with enzyme inducers. Histological examination can help distinguish primary irritants, contact sensitizers and 'autoimmunogenic' compounds. That a Graft-vs-Host (GvH)-like mechanism may be involved was further substantiated by the finding that histological features of a positive PLNA response to, e.g. streptozotocin, were quite similar to those of a 'true' local GvH response. In addition, this model is expected to be useful to improve our understanding of the mechanism(s) involved in systemic autoimmune reactions by studying the profile of PLN lymphocyte subpopulations and of released cytokines.

Immunotoxicity of subchronic versus chronic exposure to aldicarb in mice

In this study we compared the immunotoxicity of subchronic vs chronic exposure to the aldicarb insecticide at a relatively low, 0.1-10 ppb, level in drinking water. The immunotoxicity of aldicarb was evaluated in 28- and 90-day studies by determination of the humoral, cellular and nonspecific immunity in inbred C57BL/6 mice. Quantification of splenic plaque-forming cells (PFC) to sheep erythrocytes (SRBC), mitogen activation of spleen lymphocytes, mixed lymphocyte reaction (MLR) and the cytofluorometric assay of the phagocytic uptake of fluorescent beads were among the parameters studied. Neither the cell viability nor the splenic cell count was affected by the insecticide exposure. Immunophenotyping and cytometric determination of L3T4+, Lyt2+ and Ig+ cells revealed no effect of the insecticide exposure on the total count of cell subsets in the ungated splenocyte population. However, a marked shift in the percentages of L3T4+ and Lyt2+ cells was noted after subchronic exposure to 1 and 10 ppb aldicarb, possibly indicating activation of these splenic T-cell subsets. Subchronic aldicarb exposure significantly suppressed the splenic PFC response to SRBC at 1 ppb dose, however, no dose-effect correlation could be concluded. Similarly, no dose-effect correlation was observed for subchronic aldicarb-related changes in mitogen responses. Subchronic exposure to aldicarb had no statistically significant effect on the mixed lymphocyte reaction (MLR) or on the macrophage phagocytosis. Chronic exposure to 0.1-10 ppb aldicarb did not affect any of the parameters measured, including the cell subsets. Thus, aldicarb-related changes in immune parameters, noted after a 28-day exposure, were compensated over chronic exposure to the insecticide.