A nonradioisotopic endpoint for measurement of lymph node cell proliferation in a murine allergic contact dermatitis model, using bromodeoxyuridine immunohistochemistry

Lack of Acute Toxicity and Mutagenicity from Recombinant Epinephelus lanceolatus Piscidin Expressed in Pichia pastoris

The antimicrobial peptide (AMP) piscidin was identified from Epinephelus lanceolatus and demonstrated to possess antimicrobial and immune-related functions. Supplementation of feed with recombinant Epinephelus lanceolatus piscidin (rEP)-expressing yeast pellets may minimize the excessive use of antibiotics and control pathogens in aquaculture or animal husbandry. However, before implementing rEP as a supplement, it is necessary to understand whether it harbors any toxicity. Since toxicological information on the topic is scarce, the present investigation was carried out to test whether rEP exhibits allergenic and/or toxic effects. In an oral acute toxicity test (OECD 425), Sprague Dawley (SD) rats were administered rEP dissolved in reverse osmosis water, yielding an LD₅₀ > 5000 mg/kg (no observed animal death). The compound was therefore classified as non-toxic by oral administration. In an acute respiratory toxicity test (OECD 403), heads and noses of SD rats were exposed to liquid aerosol for 4 h (the highest concentration that could be administered without causing any animal death), and a lethal concentration (LC₅₀) > 0.88 mg/L was obtained. The mass medium aerodynamics diameter (MMAD) of rEP aerosol particles was 8.18 μm and mass medium aerodynamics diameter (GSD) was 3.04, which meant that 25.90% could enter the airway (<4 μm) of a rat, and 58.06% (<10 μm) could be inhaled by humans. An ocular irritation test (OECD 405) with rEP powder was performed on New Zealand White (NZW) rabbits. Signs of irritation included conjunctival swelling and diffuse flushing 1 h after administration. The signs were less apparent after 24 h and disappeared after 72 h. The classification assigned to the powder was mild eye irritation. Skin sensitization was performed for a local lymphoproliferative test (OECD 442B) using BALB/c mice, with the highest soluble concentration of the rEP considered to be 100% test substance; formulations were diluted to 50% and 25%, and bromodeoxyuridine (BrdU) incorporation was used to measure the degree of lymphocyte proliferation. The stimulation indexes (SIs) were 1.06 (100%), 0.44 (50%), and 0.77 (25%), all of which were less than the cutoff value for a positive sensitization result (1.6). Negative response was also seen in the bacterial reverse mutation test (OECD 471), and no chromosomal effects on Chinese hamster ovary (CHO)-K1 cells were observed (OECD 487). Based on these six toxicity tests, rEP showed neither acute toxic effects in experimental animals nor mutagenicity. Thus, rEP can be considered safe for use in subsequent research on its application as a feed additive for poultry, cattle, or aquatic animals.

Bathing effects of east saline groundwater concentrates on allergic (atopic) dermatitis-like skin lesions induced by 2,4-dinitrochlorobenzene in hairless mice

In the present study, it was evaluated whether east saline groundwater concentration solution (ESGWc) exerted a favorable inhibitory effect on 2,4-dinitrochlorobenzene (DNCB)-induced allergic/atopic-like dermatitis (AD). AD was induced and boosted by sensitization with DNCB via topical application on the dorsal back skins. Mice with DNCB-induced AD were bathed in 100-, 200- and 400-fold diluted ESGWc. After 6 weeks bathing, changes to body weight, clinical skin severity scores, scratching behavior, serum total immunoglobulin (Ig)E levels, submandibular lymph node and spleen weights, splenic cytokine levels, skin cytokine mRNA expressions, antioxidant defense systems and superoxide anion productions were recorded to determine the effects of bathing on the histopathology of dorsal back skin tissues. All DNCB-induced mice demonstrated that the induction of AD through IgE-mediated hypersensitivities, oxidative stresses, activation of MMP and apoptosis of keratinocytes resulted in no significant differences in body weight between the different groups at each time point following initial sensitization. However, markers of DNCB-induced AD were significantly inhibited (P<0.05) in a concentration-dependent manner following bathing in all concentrations of ESGWc. The results obtained in the present study suggest that bathing in ESGWc may have favorable protective effects against DNCB-induced AD due to favorable systemic and local immunomodulatory effects, active cytoprotective anti-apoptotic effects, inhibitory effects of matrix metalloproteinase activity, and anti-inflammatory and antioxidative effects.

Bathing Effects of Various Seawaters on Allergic (Atopic) Dermatitis-Like Skin Lesions Induced by 2,4-Dinitrochlorobenzene in Hairless Mice

We evaluated the preventive effects of four types of seawater collected in Republic of Korea on hairless mice with 2,4-dinitrochlorobenzene- (DNCB-) induced allergic/atopic dermatitis (AD). The anti-inflammatory effects were evaluated by measuring tumor necrosis factor- (TNF-) α and interleukins (ILs). Glutathione (GSH), malondialdehyde (MDA), superoxide anion, and inducible nitric oxide synthase (iNOS) were measured to evaluate the antioxidant effects. Caspase-3 and poly (ADP-ribose) polymerase (PARP) were observed to measure the antiapoptotic effects; matrix metalloproteinase- (MMP-) 9 levels were also evaluated. Mice with AD had markedly higher clinical skin severity scores and scratching behaviors; higher TNF-α and ILs (1β, 10, 4, 5, and 13) levels; higher MDA, superoxide anion, caspase-3, PARP, and MMP-9 levels; and greater iNOS activity. However, the severity of AD was significantly decreased by bathing in seawaters, but it did not influence the dermal collagen depositions and skin tissue antioxidant defense systems. These results suggest that bathing in all four seawaters has protective effects against DNCB-induced AD through their favorable systemic and local immunomodulatory effects, active cytoprotective antiapoptotic effects, inhibitory effects of MMP activity and anti-inflammatory and antioxidative effects.

Investigation of the dermal sensitizing potential of traditional medical extracts in local lymph node assays

Traditional medical extracts are commonly used as complex mixtures, which may contain naturally occurring contact sensitizers. In this investigation, the mice local lymph node assay (LLNA) was performed to evaluate the dermal sensitization potential of Myrrh, Borneolum, Olibanum, Moschus and Cassia Bark, which are widely used in topical traditional medication. In the radioactive LLNA, the stimulation index (SI) values were calculated for each medical extract. Myrrh, Borneolum, Olibanum and Moschus induced dose-dependent cell proliferation and SI was more than 3. Cassia Bark showed no positive response over the range of test concentrations. In the flow cytometry analysis, the total number of CD3(+), CD4(+), and CD8(+) cells in local lymph nodes was increased in Moschus-, Olibanum-, Myrrh- and Borneolum-treated mice. The ratio of the B220(+)/CD3(+) (B/T cell ratio) and the percentage of I-A(k+) cells that was also positive for the CD69 marker (I-A(k+)/ CD69(+)) were increased in the Moschus-, Olibanum- and Myrrh-treated mice. However, no ofbvious change was observed in Borneolum-treated mice. Cassia Bark did not induce changes in the lymphocyte subpopulations. These results indicate that Moschus, Olibanum and Myrrh can be regarded as sensitizers, and Borneolum regarded as an irritant. Cassia Bark is neither a sensitizer nor an irritant. The combination of radioactive and flow cytometric LLNA can be used for the prediction of sensitizing potential of medical extracts which lead to allergic contact dermatitis in humans.

Application of a Systems Biology Approach to Skin Allergy Risk Assessment

We have developed an in silico model of the induction of skin sensitisation, in order to characterise and quantify the contribution of each pathway to the overall biological process. This analysis has been used to guide our research on skin sensitisation and in vitro test development programmes, and provides a theoretical rationale for the interpretation and integration of non-animal predictive data for risk assessment (RA) purposes. The in vivo mouse Local Lymph Node Assay (LLNA) is now in widespread use for the evaluation of skin sensitisation potential and potency. Recent changes in European Union (EU) legislation (i.e. the 7th Amendment to the EU Cosmetics Directive) have made the development of non-animal approaches to provide the data for skin sensitisation RA a key business need. Several in vitro predictive assays have already been developed for the prediction of skin sensitisation. However, these are based on the determination of a small number of pathways within the overall biological process, and our understanding of the relative contribution of these individual pathways to skin sensitisation induction is limited. To address this knowledge gap, a “systems biology” approach has been used to construct a computer-based mathematical model of the induction of skin sensitisation, in collaboration with Entelos, Inc. The biological mechanisms underlying the induction phase of skin sensitisation are represented by nonlinear ordinary differential equations and defined by using information from over 500 published papers. By using the model, we have identified knowledge gaps for future investigative research, and key factors that have a major influence on the induction of skin sensitisation (e.g. TNF-α production in the epidermis). The relative contribution of each of these key pathways has been assessed by determining their contributions to the overall process (e.g. sensitiser-specific T-cell proliferation in the draining lymph node). This information provides a biologically-relevant rationale for the interpretation and potential integration of diverse types of non-animal predictive data. Consequently, the Skin Sensitisation Physiolab® (SSP) platform represents one approach to integration that is likely to prove an invaluable tool for hazard evaluation in a new framework for consumer safety RA.

Heavy water labeling of DNA for measurement of cell proliferation and recruitment during primary murine lymph node responses against model antigens

Lymph node (LN) responses to antigens involve inflammatory lymphocyte recruitment and proliferation of rare antigen-specific precursors; the relative contributions of these processes have not been well quantified. The popliteal LN assay (PLNA), used for immunotoxicity screening, measures LN swelling as a surrogate of antigen-specific immunity, but nonspecific irritants cause false-positive results. Quantification of proliferating cells may improve specificity, but commonly-used biosynthetic labels (e.g., BrdU) have limitations. In vivo labeling with heavy water ((2)H(2)O) is nontoxic and (2)H incorporation into the DNA of dividing cells highly consistent, even in apoptotic microenvironments such as the thymus. Here, we have used continuous (2)H(2)O labeling and GC/MS analysis to quantify the cumulative fraction of recently divided cells (f) in draining LN of mice. Priming of BALB/c mice with model antigens (KLH, DNCB) increased both LN cell counts and f in responding lymphocyte subsets, whereas lymphocyte recruitment to LN by irritants (IFA, DMSO) increased cell counts but had little effect on f. Thus, antigen-driven proliferation (possibly including a bystander component) was reflected in f, whereas LN cellularity was primarily increased by recruitment. Cell counts responded differentially to changes in Ag dose and immunization with IFA, whereas f was unaffected by these variables. GC/MS analysis of (2)H(2)O-labeled lymphocyte DNA affords sensitive, precise measurements of fractional lymphoproliferation. Dissection of proliferation and cell recruitment by this approach may be useful for preclinical in vivo screening of novel adjuvants and immunomodulatory agents, for studying their mechanism of action, and for immunotoxicity screening in the PLNA.

Interlaboratory validation of the modified murine local lymph node assay based on adenosine triphosphate measurement

INTRODUCTION

The murine local lymph node assay (LLNA) is a well-established alternative to the guinea pig maximization test (GPMT) or Buehler test (BT) for the assessment of the skin sensitizing ability of drugs and chemicals. Daicel Chemical Industries Ltd. has developed a modified LLNA based on the adenosine triphosphate (ATP) content (LLNA-DA). We conducted 2 interlaboratory validation studies to evaluate the reliability and relevance of LLNA-DA.

METHODS

The experiment involved 17 laboratories, wherein 14 chemicals were examined under blinded conditions. In the first study, 3 chemicals were examined in 10 laboratories and the remaining 9 were examined in 3 laboratories. In the second study, 1 chemical was examined in 7 laboratories and the remaining 4 chemicals were examined in 4 laboratories. The data were expressed as the ATP content for each chemical-treated group, and the stimulation index (SI) for each chemical-treated group was determined as the increase in the ATP content relative to the concurrent vehicle control group. An SI of 3 was set as the cut-off value for exhibiting skin sensitization activity.

RESULTS

The results of the first study obtained in the experiments conducted for the 3 chemicals that were examined in all the 10 laboratories and for 5 of the remaining 9 chemicals were sufficiently consistent with small variations in their SI values. The sensitivity, specificity, and accuracy of LLNA-DA against those of GPMT/BT were 7/8 (87.5%), 3/3 (100%), and 10/11 (90.9%), respectively. In the second study, all the 5 chemicals studied demonstrated acceptably small interlaboratory variations.

DISCUSSION

In the first study, a large variation was observed for 2 chemicals; in the second study, this variation was small. It was attributed to the application of dimethylsulfoxide as the solvent for the metallic salts. In conclusion, these 2 studies provide good evidence for the reliability of the LLNA-DA.

Characterization and evaluation of a modified local lymph node assay using ATP content as a non-radio isotopic endpoint

INTRODUCTION

The murine local lymph node assay (LLNA) is an accepted and widely used method for assessing the skin-sensitizing potential of chemicals. Here, we describe a non-radio isotopic modified LLNA in which adenosine triphosphate (ATP) content is used as an endpoint instead of radioisotope (RI); the method is termed LLNA modified by Daicel based on ATP content (LLNA-DA).

METHODS

Groups of female CBA/JNCrlj mice were treated topically on the dorsum of both ears with test chemicals or a vehicle control on days 1, 2, and 3; an additional fourth application was conducted on day 7. Pretreatment with 1% sodium lauryl sulfate solution was performed 1 h before each application. On day 8, the amount of ATP in the draining auricular lymph nodes was measured as an alternative endpoint by the luciferin-luciferase assay in terms of bioluminescence (relative light units, RLU). A stimulation index (SI) relative to the concurrent vehicle control was derived based on the RLU value, and an SI of 3 was set as the cut-off value.

RESULTS

Using the LLNA-DA method, 31 chemicals were tested and the results were compared with those of other test methods. The accuracy of LLNA-DA vs LLNA, guinea pig tests, and human tests was 93% (28/30), 80% (20/25), and 79% (15/19), respectively. The estimated concentration (EC) 3 value was calculated and compared with that of the original LLNA. It was found that the EC3 values obtained by LLNA-DA were almost equal to those obtained by the original LLNA.

DISCUSSION

The SI value based on ATP content is similar to that of the original LLNA as a result of the modifications in the chemical treatment procedure, which contribute to improving the SI value. It is concluded that LLNA-DA is a promising non-RI alternative method for evaluating the skin-sensitizing potential of chemicals.

Evaluation of immunotoxicity induced by pirimiphos-methyl in male Balb/c mice following exposure to for 28 days

Pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethyl phosphorothioate: POM) is widely used organophosphorous (OP) insecticide as a grain protectant to control insects during storage. This study was carried out to assess the immunologic effects of POM in Balb/c mice after 28-day oral exposure. Three dose levels of POM (10, 60, or 120 mg/kg/day) were administered orally to mice for 4 weeks. At autopsy after 28-day exposure, there were significant decreases in relative spleen weight and splenic cellularity found at 120 mg POM, but body weight, relative thymic weight, thymic cellularity, and splenic and thymic subsets were not affected. T cell proliferation response induced by Con A was significantly decreased at all dosages though no statistical differences were observed in splenic B cell proliferation. Significant increases in the production of cytokines (IL-2, IL-4, IL-6, IFN-gamma, and IL-10) were evident on the whole, but the increase in production of inflammatory cytokines overwhelmed that of the T(H)1 cell suppressive cytokine (IL-10). The relative levels of three types of autoantibodies, anti-dsDNA, anti-histone, and antinuclear antibody (ANA) were dose-dependently decreased in serum. Oral exposure to POM induced a significant decrease in Immunoglobulin M production capability in Balb/c mice. This decrease in antibody production capability may result from disturbances in cytokine balance produced by splenic immune cells. These results show that POM may induce allergic responses by relatively enhancing T(H)2 development and additionally contribute to chronic inflammation by attracting macrophage by IFN-gamma.

Maternal allergic contact dermatitis causes increased asthma risk in offspring

Background

Offspring of asthmatic mothers have increased risk of developing asthma, based on human epidemiologic data and experimental animal models. The objective of this study was to determine whether maternal allergy at non-pulmonary sites can increase asthma risk in offspring.

Methods

BALB/c female mice received 2 topical applications of vehicle, dinitrochlorobenzene, or toluene diisocyanate before mating with untreated males. Dinitrochlorobenzene is a skin-sensitizer only and known to induce a Th1 response, while toluene diisocyanate is both a skin and respiratory sensitizer that causes a Th2 response. Both cause allergic contact dermatitis. Offspring underwent an intentionally suboptimal protocol of allergen sensitization and aerosol challenge, followed by evaluation of airway hyperresponsiveness, allergic airway inflammation, and cytokine production. Mothers were tested for allergic airway disease, evidence of dermatitis, cellularity of the draining lymph nodes, and systemic cytokine levels. The role of interleukin-4 was also explored using interleukin-4 deficient mice.

Results

Offspring of toluene diisocyanate but not dinitrochlorobenzene-treated mothers developed an asthmatic phenotype following allergen sensitization and challenge, seen as increased Penh values, airway inflammation, bronchoalveolar lavage total cell counts and eosinophilia, and Th2 cytokine imbalance in the lung. Toluene diisocyanate treated interleukin-4 deficient mothers were able to transfer asthma risk to offspring. Mothers in both experimental groups developed allergic contact dermatitis, but not allergic airway disease.

Conclusion

Maternal non-respiratory allergy (Th2-skewed dermatitis caused by toluene diisocyanate) can result in the maternal transmission of asthma risk in mice.

Evaluation of the potential immunotoxicity of 3-monochloro-1,2-propanediol in Balb/c mice

3-Monochloro-1,2-propanediol (MCPD) is a well-known by-product of acid-hydrolyzed soy sauce during its manufacturing process. To evaluate the immunotoxicity of MCPD, we investigated its effect on the thymic subset, delayed-type hypersensitivity, mixed-lymphocyte reaction and peritoneal macrophage activity. MCPD was administered by gavage for 14 days at 0, 25, 50, and 100 mg/kg/day to female Balb/c mice. The thymic subsets and annexin-V positive cells in thymic cells were quantified by flow cytometry. Mixed-lymphocyte reaction, delayed-type hypersensitivity and peritoneal macrophage activity were assessed. The mixed-lymphocyte reaction and delayed-type hypersensitivity were not significantly changed. However, there were significant increases in the apoptosis of mice treated with high dose of MCPD compared to the vehicle control. A significant decrease in the CD4+CD8+ thymic subset of mice treated with high dose of MCPD was observed. The activity of peritoneal macrophage was significantly reduced in high dose group. These results indicate that MCPD could modulate the immune function in Balb/c mice.

Modulation of intracellular cytokines in draining lymph node cells following allergen and irritant

The murine local lymph node assay (LLNA) has been developed as an alternative to guinea pig models for the assessment of the contact sensitization potential. However, there is a need to develop a non-radioisotopic endpoint for the LLNA because of the radioisotopic method's requiring the use of special facilities. In this study, we investigated to evaluate the populations of intracellular cytokine producing cells and to analyze the expression of mRNA levels in the lymph node (LN) cells following allergen and irritant. Female Balb/c mice were treated by the topical application on the dorsum of both ears with strong sensitizers, 2,4-dinitrochlorobenzene (DNCB) and toluene diisocyanate (TDI) and a strong irritant, sodium lauryl sulfate (SLS), once daily for 3 consecutive days. The lymph node cells were harvested 72h after the final treatment. The analysis of intracellular cytokine cell in LN cells was performed with a flow cytometry. Mice were treated with DNCB and TDI showed a preferential increase in the percentage of CD4+IL-2+ cells compared with vehicle and irritant-treated mice. There was an increase in CD4+IFN-g+ cells of mice treated with DNCB and TDI, but no significant increases were observed in mice treated with SLS. Mice were treated with DNCB and TDI showed an increase in the percentage of CD4+IL-4+ cells compared with vehicle and irritant-treated mice. There was an increase in the mRNA level for interleukin 4 (IL-4) in mice treated with DNCB and TDI, but no significant increases were observed in mice treated with SLS. These results suggest that the population of interferon-gamma (IFN-g+) and IL-4+ cells on CD4+ cells and the mRNA expression for IL-4 in lymphocytes could be selectively modulated in allergen-treated mice.

Clinical relevance of preclinical testing for allergic side effects

Immune-mediated hypersensitivity reactions include exaggerated humoral or cell mediated responses to specific antigens and may culminate in adverse, potentially life threatening effects. The immune status of the host and presence of infections or other disorders can alter the kind and extent of immune mediated side effects in individuals. Such variability in the immune status may influence the type of idiosyncratic reaction(s) that patients manifest. The issues typically encountered from a drug development standpoint include the potential for contact hypersensitivity, respiratory sensitivity, systemic hypersensitivity, photoallergy, and pseudoallergy. There are no accepted in vitro or in vivo models available to measure and predict all types of hypersensitivity reactions in humans. There is a need for the development of preclinical models to predict all types of hypersensitivity reactions in humans. The FDA immunotoxicology guidance document recommends doing preclinical testing in animal models for topical and inhalational drugs before initiation of multiple dose studies in humans. Any signs of potential immune related drug hypersensitivity should be further evaluated in an attempt to further understand the potential for hypersensitivity reactions in humans. In summary, existing preclinical models have limited capability for prediction of drug allergy in humans except for topical and inhalational drugs. Additional tools are needed to evaluate drugs in early development and improve performance of existing assays.

Advantage of using CBA/N strain mice in a non-radioisotopic modification of the local lymph node assay

The murine local lymph node assay (LLNA) is currently recognized as a stand-alone test method for determining the skin sensitizing potential of chemicals. It has been incorporated into the official test guidelines published by some authorities, including the OECD. To avoid the use of radioisotopes, efforts have been made recently to develop non-radioisotopic modifications of the LLNA. A non-radioisotopic modification of the LLNA was developed previously using 5-bromo-2'-deoxyuridine (BrdU) incorporation (non-RI LLNA). However, the non-RI LLNA was found to be somewhat less sensitive than the standard assay. This study reports the advantage of using mice of the CBA/N strain in the non-RI LLNA to improve the sensitivity of this method. The non-RI LLNA was performed using CBA/JN and CBA/N mice exposed to one of four confirmed skin sensitizers, 2,4-dinitrochlorobenzene (DNCB), eugenol (EG), isoeugenol (IEG) or alpha-hexylcinnamic aldehyde (HCA), and to one non-sensitizer, propylene glycol (PG). The EC3 values for DNCB, IEG, EG, HCA and PG were calculated to be 0.1%, 9.6%, 40.6%, 45.5% and >50% in CBA/JN mice and 0.08%, 1.9%, 10.7%, 20.3% and >50% in CBA/N mice, respectively. The EC3 values for DNCB, IEG, EG, HCA and PG in the standard LLNA using CBA/Ca mice and radioisotopes were reported elsewhere as being 0.08%, 1.3%, 13.0%, 8.0% and >50%, respectively. The EC3 values derived from the CBA/N mice in the non-RI LLNA were nearly equivalent to the EC3 values obtained using the standard radioisotopic LLNA with CBA/Ca mice. These data suggest that the use of CBA/N mice may provide a realistic opportunity to develop a version of the LLNA that does not have a requirement for the use of radioisotopes, but which nevertheless has sensitivity approaching, or comparable to, the standard method.

Evaluation of the potential immunotoxicity of 3-monochloro-1,2-propanediol in Balb/c mice

3-Monochloro-1,2-propanediol (MCPD) is a well-known by-product of acid-hydrolyzed soy sauce during its manufacturing process. MCPD has been reported genotoxic in vitro, and reproductive toxicity and carcinogenicity in rats. However, no previous studies have investigated MCPD-induced alterations in the immune system. In the present study, MCPD was administered by gavage for 14 days at 0, 25, 50, and 100 mg/kg per day to female Balb/c mice. The antibody-mediated immune response to sheep red blood cells (SRBC) was assessed using the antibody-forming cell (AFC) assay, and splenic cell phenotypes were quantified by flow cytometry. Hematological and histopathological changes were assessed. Mitogen-stimulated spleen lymphocyte proliferation and natural killer (NK) cell activity were evaluated. The T-lymphocyte blastogenesis by concanavalin A (Con A) or anti-CD3 and B-lymphocyte blastogenesis by lipopolysaccharide (LPS) were not significantly changed. There were no significant changes in the hematological and histopathological findings of MCPD-treated mice. However, the significant decrease in thymus weight was observed in 100 mg dose group, even though that did not change body weight gain. The cellularities of spleen and thymus were significantly reduced in high-dose group. Exposure to high dose of MCPD decreased the AFC response to SRBC in mice. There was a significant decrease in NK cell activity of mice treated with high dose of MCPD. These results indicate that MCPD could modulate the immune function in Balb/c mice.

Evaluation of lymphocyte subpopulations in draining lymph node cells following allergen and irritant

The murine local lymph node assay (LLNA) has been developed as an alternative to guinea pig models for the assessment of the contact sensitization potential. However, there is a need to develop a non-radioisotopic endpoint for the LLNA, because of the radioisotopic method's requiring the use of special facilities. In this study, we investigated to evaluate the lymphocyte subpopulations in the lymph node cells following allergen and irritant treatment. Female Balb/c mice were treated by the topical application on the dorsum of both ears with sensitizers, 2,4-dinitrochlorobenzene (DNCB), toluene diisocyanate (TDI), and α-hexylcinnamaldehyde (HCA), and an irritant, sodium lauryl sulfate (SLS), once daily for three consecutive days. The lymph node (LN) cells were harvested 72h after the final treatment. Phenotypic analysis of lymphocytes subsets was performed with a flow cytometry. The allergens DNCB, TDI, and HCA and an irritant, SLS increased cell number compared to the vehicle. Mice were treated with DNCB, HCA, and TDI showed a preferential increase in the percentage of B220+CD40+ cells compared with vehicle and irritant-treated mice. There was an increase in B220+CD86+ cells of mice treated with DNCB, TDI, and HCA, but no significant increases were observed in mice treated with SLS. Mice were treated with DNCB and TDI showed an increase in the percentage of B220+CD23+ cells compared with vehicle and irritant-treated mice. These results suggest that analysis of B cell activation marker, CD40 on B cells may be useful in differentiating allergen and irritant responses in the draining lymph nodes of chemically treated mice.