Kinetics and morphology of chemically induced popliteal lymph node reactions compared with antigen-, mitogen-, and graft-versus-host-reaction-induced responses

Popliteal lymph node (PLN) assay to study adjuvant effects on respiratory allergy

Different variants of the popliteal lymph node (PLN) assay have been published. Here we describe the adjuvant popliteal lymph node assay, an immune response assay to study the adjuvant activity of soluble substances as well as particulate matter. The substance to be studied for adjuvant activity is injected into the hind footpad of mice or rats together with an antigen. Adjuvant activity is determined as the increase in PLN weight and cell numbers in animals receiving antigen together with the substance under study, compared with PLN weight and cell numbers in animals given the antigen without the substance in question, and animals given the putative adjuvant alone. Because lymph node weight and cell numbers are immunologically non-specific parameters, specific immune response assays like serum antibody responses or antibody-forming cell numbers should additionally be performed. Different antigens and immune response assays may be used, depending on the research question asked. In relation to respiratory (or food) allergy, the assays should as a minimum include determination of specific IgE in serum, and preferably also IgG1 (mouse). Serum specific IgG2a antibody determination may be added to get an indication of the Th1-Th2-balance of the response. The adjuvant PLN assay, with cellular response assays performed in the draining popliteal lymph node and antibody determinations in serum, requires small amounts of test material. The assay offers a practical, sensitive and reproducible method to determine the adjuvant activity of soluble substances as well as particulate material, with the possibility to also perform mechanistic studies.

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.

Oxazolone and diclofenac-induced popliteal lymph node assay reactions are attenuated in mice orally pretreated with the respective compound: potential role for the induction of regulatory mechanisms following enteric administration

The murine popliteal lymph node assay (PLNA) was examined as a preclinical assay with the potential to identify low-molecular-weight compounds (LMWCs) that are likely to be associated with immune-mediated drug hypersensitivity reactions (IDHRs) in humans. We hypothesized that the contact sensitizer oxazolone (OX) would cause a strong PLN reaction in naive mice and that the PLN reaction would be attenuated in mice orally pretreated with OX due to the induction of oral tolerance. In naive mice, OX induced a strong PLN reaction and caused dose-dependent increases in PLN size, weight, cellularity, percentage of CD4(+) PLN T cells, and percentage of PLN B cells, with a concomitant decrease in the percentage of CD8(+) PLN T cells. Next, the PLNA was conducted in mice gavaged three times with either OX or vehicle alone (olive oil). Mice pretreated with OX had suppressed PLN reactions following the footpad injection of OX (decrease in PLN size, weight, and cellularity), which was associated with an increase in the percentage of PLN CD8(+)T cells. In contrast, oral pretreatment with OX had no observable effect on the PLN reaction induced following footpad injection of the irrelevant hapten dinitrochlorobenzene (DNCB). Adoptive transfer studies were conducted to examine the mechanism of PLN hyporesponsiveness. It was found that either (1) unfractionated splenocytes or (2) purified CD8(+) splenocytes, but not (3) purified CD4(+) splenocytes isolated from mice gavaged with OX adoptively transferred PLN suppression to naive BALB/c mice. Because OX is not a pharmaceutical, we also examined the NSAID diclofenac (DF) (Voltaren). Like OX, DF caused dose-dependent increases in PLN size, weight, and cellularity in naive mice. Furthermore, like OX, the diclofenac-induced PLN reaction was attenuated in mice that had been orally pretreated three times with DF. However, splenocytes from mice orally treated with DF were not able to adoptively transfer PLN hyporesponsiveness. Collectively, these observations demonstrate that both OX and DF are potent immunostimulators in the PLNA. As importantly, these results demonstrate that the immunostimulating potential of OX and DF in the PLNA is significantly decreased in mice orally exposed to the respective drug, possibly due to the presence of a cellular mechanism of oral tolerance. For OX, the mechanism appears to involve, in part, CD8(+) T cells, whereas the mechanism(s) associated with PLN hyporesponsiveness using DF remain to be defined.

Positive responses to imipramine in the popliteal lymph node assay are due to primary irritation

The popliteal lymph node (PLN) assay has long been proposed as a tool to detect immunotoxicants with the potential to induce systemic autoimmunity. A major problem hampering the further validation of this assay is the need to rule out irritants that cause false-positive PLN responses. The anti-depressant, imipramine, has not been reported to induce systemic autoimmune reactions in treated patients, but has been repeatedly found positive in the PLN assay, suggesting that this is a false-positive response. To test this hypothesis, the effects of imipramine were compared to those of 50% ethanol in C57B1/6 mice. Footpad edema was evidenced in the few days after injection of both ethanol and imipramine. T-cell depletion using monoclonal antibodies against either CD4+ or CD8+ T-lymphocytes prior to the PLN assay did not influence the responses to either ethanol or imipramine. Cytokine (TNFalpha, IL-1alpha, IL-1beta, IL-2R, IL-6, IL-12 and IFN-gamma) fingerprinting of the PLNs after injection of ethanol and imipramine evidenced the same pattern of responses. These results indicate a closely similar pattern of responses following the footpad injection of either imipramine or ethanol. The conclusion can be drawn that imipramine induces positive responses in the PLN assay via primary (nonspecific) irritation.

Histopathologic approaches to detect changes indicative of immunotoxicity

Toxicologic pathology is crucial in the identification and characterization of health effects following exposure to xenobiotics, mainly in toxicity experiments in rodents. Regarding regulatory toxicology, histopathology of lymphoid organs and tissues is a cornerstone in the identification of immunotoxic compounds. A 2-tier testing system is usually employed in which the first tier is a general screen for (immuno)toxicity and the second tier consists of specific immune function studies, including host resistance tests or mechanistic studies. The role attributed to histopathology of lymphoid organs in the updated Organisation for Economic Cooperation and Development and Food and Drug Administration guidelines requires improvement and standardization of the histopathology procedures. Optimalization and standardization was started in an international collaborative immunotoxicity study (ICICIS). However, several problems were left unaddressed, mostly because of the few compounds tested in this study. Based on the results of the ICICIS study and the morphologic changes induced by immunotoxic/immunomodulatory compounds observed in other investigations, suggestions are given to further improve the identification and (semi)quantification of histopathologic changes in lymphoid organs and tissues.

Hexachlorobenzene-induced immunomodulation and skin and lung lesions: a comparison between brown Norway, Lewis, and Wistar rats

Strain dependence of the induction of skin and lung lesions by hexachlorobenzene (HCB) in the rat was studied to further the insight into the etiology of the lesions. To this end, 3- to 4-week-old female Brown Norway (BN), Lewis, and Wistar rats received diets supplemented with 150 mg (BN and Lewis), 450 mg (BN, Lewis, and Wistar) or 900 mg (BN and Wistar) HCB per kilogram diet for 4 weeks. Gross skin lesion development during exposure as well as pathologic changes in skin and lungs and various parameters of immunomodulation after exposure were assessed. General toxicity as judged by a slight increase in body weight gain and induction of liver cell hypertrophy was similar in BN and Lewis rats exposed to 450 mg/kg HCB and in Wistar rats exposed to 900 mg/kg HCB. Skin lesions ranged from redness to large exudating sores with crusts. With regard to dose, time of onset, incidence, and severity, skin lesions were very severe in BN, moderate in Lewis, and negligible in Wistar. Porphyrins could not be detected in the skin, whereas porphyrins in the liver were seen only in Lewis rats. Histology showed epidermal hyperplasia, deep dermal venules with activated endothelium, and deep dermal inflammatory infiltrates mainly consisting of eosinophilic granulocytes in BN and of mononuclear cells in Lewis and Wistar. Nonlesional skin of HCB-exposed rats showed very similar, though less prominent, changes. Lung pathology appeared negligibly strain-dependent; histology showed venules with an activated endothelium surrounded by a perivascular infiltrate as well as focal alveolar macrophage accumulations in all strains. Parameters of immunomodulation showed moderate strain dependence; relative spleen weights were dose-dependently increased in BN and Wistar and in the 450 mg/kg group in Lewis rats. BN rats showed a more marked splenomegaly than the other strains. Relative popliteal lymph node weights were increased significantly in BN and Lewis rats exposed to 450 mg/kg HCB. In all strains, HCB increased lymph node HEVs. Serum IgE and IgG levels were increased significantly in a dose-dependent way in BN rats only. Total serum IgM levels were elevated significantly in BN, Lewis, and Wistar rats that received 450 mg/kg and in Wistar rats that received 900 mg/kg HCB. Serum IgM levels against ssDNA were dose-dependently increased in all strains, being more marked in BN and Lewis than in Wistar rats. It is concluded that the HCB-induced inflammatory skin and lung pathologies have different etiology. Pronounced strain differences in the skin lesions suggest a specific involvement of the immune system. Skin lesions correlated significantly with all assessed parameters of immunomodulation in BN, with some in Lewis and with none in Wistar rats. No correlation was observed between the parameters of immunomodulation and lung lesions.

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.

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.

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.

Nitrofurantoin-induced pulmonary hemorrhage in a renal transplant recipient receiving immunosuppressive therapy: case report and review of the literature

A 33-year-old woman received a cadaveric renal transplant for focal segmental glomerulosclerosis. Nitrofurantoin urinary prophylaxis was started on postoperative day 13 but coughing and mild hemoptysis began 2 days later. Diffuse infiltrates and worsening hemoptysis led to intubation and open lung biopsy. Clinical course, culture results and pathological evaluation excluded infectious etiologies and were consistent with a drug reaction. The case is described, and the literature on the nitrofurantoin pulmonary toxicity syndromes and pathophysiology is reviewed.

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.