Delayed-type Hypersensitivity Lesions Research Articles

Distribution and efficacy of ofatumumab and ocrelizumab in humanized CD20 mice following subcutaneous or intravenous administration.

Approval of B-cell-depleting therapies signifies an important advance in the treatment of multiple sclerosis (MS). However, it is unclear whether the administration route of anti-CD20 monoclonal antibodies (mAbs) alters tissue distribution patterns and subsequent downstream effects. This study aimed to investigate the distribution and efficacy of radiolabeled ofatumumab and ocrelizumab in humanized-CD20 (huCD20) transgenic mice following subcutaneous (SC) and intravenous (IV) administration. For distribution analysis, huCD20 and wildtype mice (n = 5 per group) were imaged by single-photon emission computed tomography (SPECT)/CT 72 h after SC/IV administration of ofatumumab or SC/IV administration of ocrelizumab, radiolabeled with Indium-111 (111In-ofatumumab or 111In-ocrelizumab; 5 µg, 5 MBq). For efficacy analysis, huCD20 mice with focal delayed-type hypersensitivity lesions and associated tertiary lymphoid structures (DTH-TLS) were administered SC/IV ofatumumab or SC/IV ocrelizumab (7.5 mg/kg, n = 10 per group) on Days 63, 70 and 75 post lesion induction. Treatment impact on the number of CD19+ cells in select tissues and the evolution of DTH-TLS lesions in the brain were assessed. Uptake of an 111In-labelled anti-CD19 antibody in cervical and axillary lymph nodes was also assessed before and 18 days after treatment initiation as a measure of B-cell depletion. SPECT/CT image quantification revealed similar tissue distribution, albeit with large differences in blood signal, of 111In-ofatumumab and 111In-ocrelizumab following SC and IV administration; however, an increase in both mAbs was observed in the axillary and inguinal lymph nodes following SC versus IV administration. In the DTH-TLS model of MS, both treatments significantly reduced the 111In-anti-CD19 signal and number of CD19+ cells in select tissues, where no differences between the route of administration or mAb were observed. Both treatments significantly decreased the extent of glial activation, as well as the number of B- and T-cells in the lesion following SC and IV administration, although this was mostly achieved to a greater extent with ofatumumab versus ocrelizumab. These findings suggest that there may be more direct access to the lymph nodes through the lymphatic system with SC versus IV administration. Furthermore, preliminary findings suggest that ofatumumab may be more effective than ocrelizumab at controlling MS-like pathology in the brain.

Histopathological Characterization of Cutaneous Delayed-type Hypersensitivity and Correlations with Intestinal Pathology and Systemic Immune Responses in Sheep with Paratuberculosis

Cell-mediated immunity has been exploited historically in the diagnosis of mycobacterial diseases through elicitation of a delayed-type hypersensitivity (DTH) reaction following intradermal injection of an antigen. Here we describe the histopathological features of the cutaneous DTH reaction and its association with intestinal pathology and systemic immune responses in sheep with Mycobacterium avium subspecies paratuberculosis (MAP) infection. A mixed mononuclear cellular infiltrate dominated the DTH reaction and was present in perivascular and periadnexal patterns. Multiple multinucleate giant cells were present in the cellular infiltrate in one sheep while plasma cells were an obvious feature in six others. Sheep with paucibacillary intestinal lesions had the greatest degrees of cutaneous induration, more severe cellular infiltration in DTH lesions and high systemic interferon (IFN)-γ production. In contrast, sheep with multibacillary intestinal lesions, and particularly those with dissemination of MAP to extra-intestinal tissues, had minimal cutaneous induration, nil to mild cellular infiltration in DTH lesions and high serum anti-MAP antibody levels. Systemic IFN-γ production generally was augmented following skin sensitization. In general, the gross and histopathological features of the cutaneous DTH response matched the stage of paratuberculosis reflected by intestinal pathology and systemic measures of humoral and cellular immunity.

Deciphering the proteome of the in vivo diagnostic reagent “purified protein derivative” from Mycobacterium tuberculosis

Purified protein derivative (PPD) has served as a safe and effective diagnostic reagent for 60 years and is the only broadly available material to diagnose latent tuberculosis infections. This reagent is also used as a standard control for a number of in vitro immunological assays. Nevertheless, the molecular composition and specific products that contribute to the extraordinary immunological reactivity of PPD are poorly defined. Here, a proteomic approach was applied to elucidate the gene products in the U.S. Food and Drug Administration (FDA) standard PPD-S2. Many known Mycobacterium tuberculosis T-cell antigens were detected. Of significance, four heat shock proteins (HSPs) (GroES, GroEL2, HspX, and DnaK) dominated the composition of PPD. The chaperone activities and capacity of these proteins to influence immunological responses may explain the exquisite solubility and immunological potency of PPD. Spectral counting analysis of three separate PPD reagents revealed significant quantitative variances. Gross delayed-type hypersensitivity (DTH) responses in M. tuberculosis infected guinea pigs were comparable among these PPD preparations; however, detailed histopathology of the DTH lesions exposed unique differences, which may be explained by the variability observed in the presence and abundance of early secretory system (Esx) proteins. Variability in PPD reagents may explain differences in DTH responses reported among populations.

Development of IL-17-mediated Delayed-Type Hypersensitivity Is Not Affected by Down-Regulation of IL-25 Expression

IL-25, which is a member of the IL-17 family, induces Th2 cell differentiation and Th2 cytokine production, contributing to induction of Th2-type immune responses and diseases, as a result of which it suppresses Th1- and Th17-type immune responses. To elucidate the role of IL-25 in the pathogenesis of IL-17-mediated delayed-type hypersensitivity (DTH), IL-25-deficient mice were sensitized with methylated BSA (mBSA), and then a DTH reaction was induced by mBSA challenge. mBSA-specific T-cell induction was assessed on the basis of cell proliferation and cytokine production. The DTH reaction was evaluated on the basis of tissue swelling, histology and inflammatory mediator expression. IL-25 expression was markedly reduced in local DTH lesions. However, mBSA-specific Th1, Th2 and Th17 cell induction, and the mBSA-induced DTH reaction were comparable in IL-25-deficient and wild-type mice. IL-25 is not essential for differentiation of Th1, Th2 and Th17 cells in the sensitization phase or induction of local inflammation in the elicitation phase of the mBSA-induced DTH reaction.

T-cell- and macrophage-mediated axon damage in the absence of a CNS-specific immune response: involvement of metalloproteinases.

Recent evidence has highlighted the fact that axon injury is an important component of multiple sclerosis pathology. The issue of whether a CNS antigen-specific immune response is required to produce axon injury remains unresolved. We investigated the extent and time course of axon injury in a rodent model of a delayed-type hypersensitivity (DTH) reaction directed against the mycobacterium bacille Calmette-Guérin (BCG). Using MRI, we determined whether the ongoing axon injury is restricted to the period during which the blood-brain barrier is compromised. DTH lesions were initiated in adult rats by intracerebral injection of heat-killed BCG followed by a peripheral challenge with BCG. Our findings demonstrate that a DTH reaction to a non-CNS antigen within a CNS white matter tract leads to axon injury. Ongoing axon injury persisted throughout the 3-month period studied and was not restricted to the period of blood-brain barrier breakdown, as detected by MRI enhancing lesions. We have previously demonstrated that matrix metalloproteinases (MMPs) are upregulated in multiple sclerosis plaques and DTH lesions. In this study we demonstrated that microinjection of activated MMPs into the cortical white matter results in axon injury. Our results show that axon injury, possibly mediated by MMPs, is immunologically non-specific and may continue behind an intact blood-brain barrier.

Abnormalities in monocyte recruitment and cytokine expression in monocyte chemoattractant protein 1-deficient mice.

Monocyte chemoattractant protein 1 (MCP-1) is a CC chemokine that attracts monocytes, memory T lymphocytes, and natural killer cells. Because other chemokines have similar target cell specificities and because CCR2, a cloned MCP-1 receptor, binds other ligands, it has been uncertain whether MCP-1 plays a unique role in recruiting mononuclear cells in vivo. To address this question, we disrupted SCYA2 (the gene encoding MCP-1) and tested MCP-1-deficient mice in models of inflammation. Despite normal numbers of circulating leukocytes and resident macrophages, MCP-1(-/-) mice were specifically unable to recruit monocytes 72 h after intraperitoneal thioglycollate administration. Similarly, accumulation of F4/80+ monocytes in delayed-type hypersensitivity lesions was impaired, although the swelling response was normal. Development of secondary pulmonary granulomata in response to Schistosoma mansoni eggs was blunted in MCP-1(-/-) mice, as was expression of IL-4, IL-5, and interferon gamma in splenocytes. In contrast, MCP-1(-/-) mice were indistinguishable from wild-type mice in their ability to clear Mycobacterium tuberculosis. Our data indicate that MCP-1 is uniquely essential for monocyte recruitment in several inflammatory models in vivo and influences expression of cytokines related to T helper responses.

Induction of the S100 Chemotactic Protein, CP-10, in Murine Microvascular Endothelial Cells by Proinflammatory Stimuli

AbstractMicrovascular endothelial cells (EC) have multiple functions in inflammatory responses, including the production of chemoattractants that enhance leukocyte transmigration into tissues. Chemotactic protein, 10 kD (CP-10), is an S100 protein with potent chemotactic activity for myeloid cells in vitro and in vivo and is expressed in neutrophils and lipopolysaccharide (LPS)-activated macrophages. We show here that CP-10 is induced in murine endothelioma cell lines (bEnd-3, sEnd-1, and tEnd-1) after activation with LPS and interleukin-1 (IL-1) but not tumor necrosis factor α (TNFα) or interferon γ (IFNγ). Induction was not mediated by endogenous release of IL-1 or TNFα and was not directly upregulated by phorbol myristate acetate, calcium ionophore, or vitamin D3. EC were exquisitely sensitive to IL-1 activation (3.4 U/mL) and CP-10 mRNA induction with IL-1 occurred earlier (8 hours) than with LPS (12 hours). Furthermore, some microvessels and capillaries in delayed-type hypersensitivity lesions expressed cytoplasmic CP-10. Responses to LPS and not IL-1 in vitro were regulated by the degree of cell confluence and by TNFα costimulation. The related MRP-14 mRNA had a different induction pattern. Monomeric and homodimeric CP-10 upregulated by activation was predominantly cell-associated. EC-derived CP-10 may contribute to amplification of inflammatory processes by enhancing leukocyte shape changes and transmigration in the microcirculation.

Induction of the S100 Chemotactic Protein, CP-10, in Murine Microvascular Endothelial Cells by Proinflammatory Stimuli

Microvascular endothelial cells (EC) have multiple functions in inflammatory responses, including the production of chemoattractants that enhance leukocyte transmigration into tissues. Chemotactic protein, 10 kD (CP-10), is an S100 protein with potent chemotactic activity for myeloid cells in vitro and in vivo and is expressed in neutrophils and lipopolysaccharide (LPS)-activated macrophages. We show here that CP-10 is induced in murine endothelioma cell lines (bEnd-3, sEnd-1, and tEnd-1) after activation with LPS and interleukin-1 (IL-1) but not tumor necrosis factor α (TNFα) or interferon γ (IFNγ). Induction was not mediated by endogenous release of IL-1 or TNFα and was not directly upregulated by phorbol myristate acetate, calcium ionophore, or vitamin D3. EC were exquisitely sensitive to IL-1 activation (3.4 U/mL) and CP-10 mRNA induction with IL-1 occurred earlier (8 hours) than with LPS (12 hours). Furthermore, some microvessels and capillaries in delayed-type hypersensitivity lesions expressed cytoplasmic CP-10. Responses to LPS and not IL-1 in vitro were regulated by the degree of cell confluence and by TNFα costimulation. The related MRP-14 mRNA had a different induction pattern. Monomeric and homodimeric CP-10 upregulated by activation was predominantly cell-associated. EC-derived CP-10 may contribute to amplification of inflammatory processes by enhancing leukocyte shape changes and transmigration in the microcirculation.

MUC18/MCAM (CD146), an activation antigen of human T lymphocytes.

Abstract Extravasation and tissue infiltration of leukocytes and metastatic tumor cells require the regulated expression and function of adhesive and pro-proteolytic surface molecules. We demonstrate here that human T cells, upon activation, neo-express the melanoma metastasis-associated surface molecule MUC18/melanoma cell adhesion molecule (MCAM). Expression of MUC18/MCAM (CD146) on T cells could be identified with two mAbs (541-10B2 and 541-2E5) obtained after immunization with HUT102 T cells and found to react with activated T cells. The specificity of our mAbs for MUC18/MCAM (CD146) was revealed by 1) definition of the appropriate molecular mass of approximately 110 kDa unreduced and 120 kDa reduced, 2) reactivity of mAbs with MUC18/MCAM (CD146) cDNA-transfected mouse L cells, 3) conclusive crosswise immunoblotting experiments with MUC18/MCAM (CD146)-specific mAbs, and 4) N-terminal amino acid sequencing of precipitated protein. In vitro activation by PHA caused neo-expression of MUC18/MCAM (CD146) on peripheral blood T cells within 1 day of stimulation, reaching a maximum on day 3. In vivo expression of MUC18/MCAM (CD146) was confirmed on CD3+ T cells infiltrating delayed-type hypersensitivity lesions of the skin, on synovial fluid T cells of rheumatoid arthritis patients, and on distinct T leukemia cells. MUC18/MCAM (CD146) cell surface expression on activated T cells is mirrored by the presence of specific mRNA. Leukocytes of healthy donors do not show significant MUC18/MCAM (CD146) expression. The finding that MUC18/MCAM (CD146) is also expressed on activated T cells might suggest that this adhesion molecule is involved in the extravasation and/or homing of activated T cells.

Delayed-type hypersensitivity lesions in the central nervous system are prevented by inhibitors of matrix metalloproteinases

Delayed-type hypersensitivity lesions in the central nervous system are prevented by inhibitors of matrix metalloproteinases

Delayed-type hypersensitivity lesions in the central nervous system are prevented by inhibitors of matrix metalloproteinases

We have studied the effect of an inhibitor of matrix metalloproteinases, BB-1101, on a delayed-type hypersensitivity (DTK) response in the CNS. We used a recently described model in which heat-killed bacillus Calmette-Guérin (BCG) sequestered behind the blood-brain barrier (BBB) is targeted by a T-cell mediated response after subcutaneous injection of BCG (Matyszak and Perry, 1995). The DTH lesions are characterised by breakdown of the BBB, macrophage and lymphocyte infiltration and tissue damage including myelin loss. Treatment with BB-1101, which is not only a potent inhibitor of matrix metalloproteinases but also strongly inhibits TNF-α release, dramatically attenuated the CNS lesions. Breakdown of the BBB and the recruitment of T-cells into the site of the lesion were significantly reduced. There were many fewer inflammatory macrophages in DTH lesions than in comparable lesions from untreated animals. There was also significantly less myelin damage (assessed by staining with anti-MBP antibody). The DTH response in animals treated with dexamethasone was also reduced, but to a lesser degree. No significant effect was seen after administration of pentoxifylline, a phosphodiesterase inhibitor with effects including the inhibition of TNF-α production. Our results suggest that inhibitors of matrix metalloproteinases may be of considerable therapeutic benefit in neuroinflammatory diseases.

The potential role of dendritic cells in immune-mediated inflammatory diseases in the central nervous system

Dendritic cells of the rat were studied immunohistochemically with MRC OX62 monoclonal antibody and using electron microscopy. In normal CNS, a small number of OX62+ cells were detected in the choroid plexus and meninges. These cells were absent from other CNS and peripheral nervous system sites studied. Dendritic cells were also studied in two models of immune-mediated inflammatory conditions in the CNS. These were: acute experimental allergic encephalomyelitis and aberrant delayed-type hypersensitivity lesions induced as a response to heat-killed bacillus Calmette Guérin sequestrated behind the blood–brain barrier. In addition, a group of animals with a delayed-type hypersensitivity response was treated with dexamethasone to assess the effect of steroid treatment on T-cells and OX62+ cells in CNS lesions. Dendritic cells were present in many but not all lesions in acute experimental allergic encephalomyelitis and their numbers were small. In experimental allergic encephalomyelitis lesions, dendritic cells were found predominantly in perivascular cuffs, where they constituted approximately 2% of a total number of major histocompatibility complex class II+ cells. Some of these cells were also detected in the CNS parenchyma, close to the perivascular cuff. In contrast, dendritic cells were present in all delayed-type hypersensitivity lesions studied. Their number in delayed-type hypersensitivity lesions was significantly higher than in experimental allergic encephalomyelitis lesions. Numerous OX62+ cells were found, even in three-month-old lesions. Electron microscopy studies revealed that these cells were often in close contact with lymphocytes. There was no significant change in the density of both OX62+ cells, IL2R+ cells and OX19+ T-cells in delayed-type hypersensitivity lesions after seven-day treatment with dexamethasone, although there was a considerable reduction in the number of CD45RA+ T-cells. The high numbers of dendritic cells found in the delayed-type hypersensitivity lesions may be important in contributing to the chronicity of the response. They may also initiate autoimmune responses to CNS antigens uncovered during bystander tissue damage which occurs as a consequence of aberrant delayed-type hypersensitivity responses.

A comparison of leucocyte responses to heat‐killed bacillus Calmette‐Guérin in different CNS compartments

We have previously shown that heat-killed bacillus Calmette-Guérin (BCG) injected into the CNS parenchyma does not produce a typical delayed-type hypersensitivity (DTH) response [23]. In this paper we have compared the initial leucocyte response in the CNS parenchyma, ventricles and skin to gain insight into the mechanisms by which the DTH response in the CNS might be controlled. We have found that 10(5) organisms of heat-killed BCG injected into either the CNS parenchyma or the lateral ventricles produced a rapid neutrophil response at the site of the injection, which was comparable with that in the skin. The neutrophil response resolved within the first week. Unlike the neutrophil response, the mononuclear phagocyte response in the CNS parenchyma was much smaller than that seen in the ventricles and the skin and it resolved within 4 weeks. Furthermore, the myelomonocytic response in the CNS parenchyma failed to clear the BCG. The acute inflammatory response in the choroid plexus/ventricles and skin developed with a similar time-course into a typical DTH response. After the first week, lesions at these two sites were composed predominantly of T-cells and macrophages. DTH lesions were still detected at both sites after 6 weeks. The failure of the immune system to recognize foreign antigens sequestrated in the CNS parenchyma may have significant implications especially in studies of inflammatory responses in the CNS of unknown origin.

Production of the RANTES chemokine in delayed-type hypersensitivity reactions: involvement of macrophages and endothelial cells.

To understand the selective accumulation of memory T helper lymphocytes and of macrophages in delayed-type hypersensitivity (DTH) granulomas, we studied the in situ production of RANTES, a chemokine initially characterized on the basis of its in vitro chemotactic properties for each of these cell populations. RANTES gene expression was studied by in situ hybridization in 15 human lymph nodes presenting typical DTH lesions related to either sarcoidosis or tuberculosis. A positive signal was detected in all cases. Labeling was specific for the DTH lesions, as very few if any positive cells were detected in the normal residual lymphoid tissue surrounding them or in reactive lymph nodes involved in a B lymphocyte response. RANTES gene expression was associated with the production of the protein, which was detected by immunochemistry in DTH lymph nodes. The morphological characteristics and distribution of positive cells in in situ hybridization and immunochemical experiments indicated that macrophages and endothelial cells, two cell populations not previously reported to produce RANTES, contributed to its production in DTH reactions. The ability of macrophages and endothelial cells to produce RANTES was confirmed by in vitro studies with alveolar macrophages and umbilical vein endothelial cells. In view of the chemotactic properties of RANTES for a limited range of cell populations, these results suggest that RANTES production in DTH granulomas may play a role in the selective accumulation of macrophages and memory T helper lymphocytes characterizing this type of cell-mediated immune reaction, and that macrophages and endothelial cells are involved in this production.

Selective migration of the human helper-inducer memory T cell subset: confirmation by in vivo cellular kinetic studies.

The vast majority of T cells present in chronic inflammatory lesions are of the helper-inducer/memory (CD45RO+CD29+) phenotype; suppressor-inducer/naive cells (CD45RA+) are virtually absent. Furthermore, CD4+ T cells are found more frequently than CD8+ cells. Previous in vitro studies have suggested that this may be, in part, due to the increased capacity of CD45RO+CD29+ T cells to bind to endothelium and, thus, enter inflammatory foci but no in vivo evidence for preferential migration exists. To investigate this, suction blisters were generated over a purified protein derivative of tuberculin-induced delayed-type hypersensitivity lesions in humans and the phenotype of the blister cells was studied. At all time points, a preponderance of CD45RO+CD29+ cells over CD45RA+ cells and of CD4 over CD8 cells was demonstrated. Because of the rapid kinetics, this appears to represent preferential migration of these cell types rather than in situ proliferation or phenotype conversion. In addition the expression of the CD45RO but not the CD45RA antigen was up-regulated on blister T cells compared to blood T cells. Analysis of blister fluid showed high concentrations of interleukin 6 but not tumor necrosis factor-alpha or lymphotoxin. This study shows for the first time directly in vivo that CD45RO+ T cells migrate preferentially into inflammatory lesions. Furthermore, it illustrates the potential usefulness of this system in the analysis of the early phases of the immune inflammatory response.

Early Burn Wound Excision and Skin Grafting Postburn Trauma Restores In Vivo Neutrophil Delivery to Inflammatory Lesions

This study assessed the effect of early vs delayed postburn wound excision and skin grafting on the in vivo neutrophil delivery to a delayed-type hypersensitivity (DTH) reaction and a bacterial skin lesion (BSL). Male Lewis rats were presensitized to keyhole-limpet hemocyanin. Group 1 comprised sham controls. Groups 2 through 4 were given a 30% 3 degrees scald burn, but the burn wounds were excised, and skin was grafted on days 1, 3, and 7, respectively, after the burn. Group 5 comprised burn controls. Twelve days after burn trauma, all rats were injected at different intervals (during a 24-hour period) with a trio of intradermal injections of keyhole-limpet hemocyanin, Staphylococcus aureus 502A, and saline at different sites. In vivo neutrophil delivery to these dermal lesions was determined by injecting indium in 111 oxyquinoline-labeled neutrophils isolated from similarly treated groups of rats. Neutrophil delivery to DTH and BSL lesions was restored to normal by excision and skin grafting of the burn wound one day after burn trauma. Waiting three days after burn trauma to excise and skin graft the wound partially, but not completely, restored the in vivo neutrophil delivery to DTH and BSL lesions. Waiting one week to excise and skin graft a burn wound resulted in no improvement in neutrophil delivery to DTH and BSL dermal lesions. It was concluded that burn wound excision and skin grafting immediately after burn trauma restored in vivo neutrophil delivery to a BSL and DTH dermal lesion. This may, in part, explain the beneficial effect of early aggressive burn wound debridement in patients with burn injuries.

Pulmonary deposition and clearance of inhaled or instilled 198Au-colloid in the rat after the induction of pulmonary delayed type hypersensitivity reactions.

The deposition and clearance of inhaled or instilled colloidal 198Au-particles were studied in rats with pulmonary lesions induced by delayed type hypersensitivity (DTH) reactions. The increased amount of radioactivity was detected in the lung associated lymph nodes and the kidney of DTH rats on day 4 after intratracheal instillation of 198Au-particles. The initial lung deposition of inhaled 198Au-particles in the lung lobes with DTH lesions was approximately 55% of normal lobes. Early mucociliary clearance of 198Au-particles was impaired in DTH rats. These results suggest that the deposition pattern and the subsequent movements of inhaled particles in the respiratory tract might be considerably influenced by pathologic conditions in the lung.

Enhancement of the intensity, persistence, and passive transfer of delayed-type hypersensitivity lesions by pertussigen in mice.

Pertussigen, a purified protein from Bordetella pertussis, was shown to increase delayed-type hypersensitivity (DTH) to protein antigens in mice. First, it caused an approximately twofold enhancement of the magnitude of 24-h DTH reactions. Second, the peak magnitude of DTH was delayed to 4-7 d after challenge, at which time it was five times more intense than in mice not receiving pertussigen. This reaction was antigen specific, and histologically was characterized by a dense mononuclear infiltrate. Third, pertussigen prolonged DTH so that it was still detectable 3-6 wk after challenge. The effect of pertussigen was seen only in antigen-driven reactions and was time and dose dependent, with 400 ng given 3 d after immunization resulting in the most prolonged reaction. The administration of pertussigen to the recipients of sensitized lymph node cells resulted in DTH that was more intense and prolonged than the reactions in control mice. Administration of pertussigen provides a model of prolonged and enhanced T cell-dependent inflammatory responses.

A footpad weight assay method to evaluate delayed-type hypersensitivity in the mouse

Delayed-type hypersensitivity lesions have been difficult to evaluate objectively in the mouse. They are usually evaluated by measurement of footpad swelling or increased ear thickness after challenge with antigen. I have developed a footpad weight assay method which reduces the observer's error and the instrumental error. This method is reliable for the assessment of delayed-type hypersensitivity reactions when results are expressed as weight increase or weight ratio calculated on challenged and unchallenged footpad.