Impact of Food Matrices on Digestibility of Allergens and Poorly Allergenic Homologs

Background

Protease resistance is considered a risk factor for allergenicity of proteins, although the correlation is low. It is nonetheless a part of the weight-of-evidence approach, proposed by Codex, for assessing the allergenicity risk of novel food proteins. Susceptibility of proteins to pepsin is commonly tested with purified protein in solution.

Objective

Food proteins are rarely consumed in purified form. Our aim was to evaluate the impact of experimental and endogenous food matrices on protease susceptibility of homologous protein pairs with different degrees of allergenicity.

Methods

Porcine and shrimp tropomyosin (ST) were subjected to sequential exposure to amylase, pepsin, and pancreatin in their respective endogenous matrix (pork tenderloin/boiled shrimp) and in three different experimental matrices (dessert mousse [DM], soy milk [SM], and chocolate bar [CB]). Digestion was monitored by immunoblotting using tropomyosin-specific antibodies. Recombinant peach and strawberry lipid transfer protein were biotinylated, spiked into both peach and strawberry fruit pulp, and subjected to the same sequential digestion protocol. Digestion was monitored by immunoblotting using streptavidin for detection.

Results

Chocolate bar, and to a lesser extent SM, had a clear protective effect against pepsin digestion of porcine tropomyosin (PT) and to a lesser extent of ST. Increased resistance was associated with increased protein content. Spiking experiments with bovine serum albumin (BSA) confirmed the protective effect of a protein-rich matrix. The two tropomyosins were both highly resistant to pepsin in their protein-rich and lean native food matrix. Pancreatin digestion remained rapid and complete, independent of the matrix. The fat-rich environment did not transfer protection against pepsin digestion. Spiking of recombinant peach and strawberry lipid transfer proteins into peach and strawberry pulp did not reveal any differential protective effect that could explain differences in allergenicity of both fruits.

Conclusions

Protein-rich food matrices delay pepsin digestion by saturating the protease. This effect is most apparent for proteins that are highly pepsin susceptible in solution. The inclusion of food matrices does not help in understanding why some proteins are strong primary sensitizers while homologs are very poor allergens. Although for induction of symptoms in food allergic patients (elicitation), a protein-rich food matrix that may contribute to increased risk, our results indicate that the inclusion of food matrices in the weight-of-evidence approach for estimating the potential risks of novel proteins to become allergens (sensitization), is most likely of very limited value.

Safety assessment of a modified acetolactate synthase protein (GM-HRA) used as a selectable marker in genetically modified soybeans

Acetolactate synthase (ALS) enzymes have been isolated from numerous organisms including soybeans (Glycine max; GM-ALS) and catalyze the first common step in biosynthesis of branched chain amino acids. Expression of an ALS protein (GM-HRA) with two amino acid changes relative to native GM-ALS protein in genetically modified soybeans confers tolerance to herbicidal active ingredients and can be used as a selectable transformation marker. The safety assessment of the GM-HRA protein is discussed. Bioinformatics comparison of the amino acid sequence did not identify similarities to known allergenic or toxic proteins. In vitro studies demonstrated rapid degradation in simulated gastric fluid (<30s) and intestinal fluid (<1min). The enzymatic activity was completely inactivated at 50 degrees C for 15 min demonstrating heat lability. The protein expressed in planta is not glycosylated and genetically modified soybeans expressing the GM-HRA protein produced similar protein/allergen profiles as its non-transgenic parental isoline. No adverse effects were observed in mice following acute oral exposure at a dose of at least 436 mg/kg of body weight or in a 28-day repeated dose dietary toxicity study at doses up to 1247 mg/kg of body weight/day. The results demonstrate GM-HRA protein safety when used in agricultural biotechnology.

Assessment of three human FcepsilonRI-transfected RBL cell-lines for identifying IgE induced degranulation utilizing peanut-allergic patient sera and peanut protein extract

Specific IgE sera screening studies are employed to investigate protein cross-reactivity. Such nonfunctional immunochemical methods cannot measure the biological activity of proteins. Therefore, an assay using RBL cells transfected with human FcepsilonRI was developed. Our objective was to evaluate the degranulation of three cell-lines expressing either the alpha-(RBL-hEI(a)-2B12 and RBL-30/25cells) or alpha-, beta-, and gamma-subunits (RBL SX-38) of the human FcepsilonRI by beta-hexosaminidase release. Purified human IgE and serum-derived polyclonal IgE from peanut-allergic subjects following challenge with anti-IgE or peanut protein extract, respectively, were utilized. Robust degranulation was induced in all three: RBL-30/25 (84%), -hEI(a)-2B12 (54%), SX-38 (94%), respectively, using purified IgE+anti-human IgE. Good release (18%, 40-45%, and 65%, respectively) occurred for one peanut-allergic subject+peanut extract with all cell-lines. With serum from three other peanut-allergic subjects, no beta-hexosaminidase release occurred with RBL-hEI(a)-2B12 cells+peanut extract, while only serum from one subject induced good degranulation, 30% and 60%, respectively, with RBL-30/25 and RBL SX 38 cells. Consistent degranulation with a potent food allergen (peanuts) was not observed. The assay's utility in safety assessment, predictive value and reproducibility for evaluating the cross-reactivity of proteins with allergens needs further investigation with additional proteins and well-characterized sera.

Cytokine mRNA profiles for isocyanates with known and unknown potential to induce respiratory sensitization

Isocyanates are low-molecular-weight chemicals implicated in allergic asthmatic-type reactions. Identification of chemicals likely to cause asthma is difficult due to the lack of a validated test method. One hypothesis is that differential cytokine induction (Th1 versus Th2 profiles) in the draining lymph node following dermal application can be used to identify asthmagens and distinguish them from contact allergens. In this study, we compared the cytokine mRNA profiles of six chemicals: toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-tolyl(mono)isocyanate (TMI), and meta-tetramethylene xylene diisocyanate (TMXDI). Whereas TDI and MDI are well-known respiratory sensitizers, documentation for HMDI, IPDI, TMI, and TMXDI is limited, but suggests that HMDI and IPDI may have respiratory sensitization potential in humans and TMI and TMXDI do not. Following dermal exposure of BALB/c mice, all six isocyanates induced cytokines characteristic of a Th2 response. Although LLNAs suggested that the doses chosen for the RPA were immunologically equivalent, the isocyanates tested differentiated into two groups, high responders and low responders. However, two of the low responders (TMI and TMXDI) were further tested and induced higher levels of Th2 cytokine message than dinitrochlorobenzene (not an asthmagen). Further study of these chemicals is needed to determine whether the Th2 cytokine responses observed for these low responders is predictive of asthmagenic potential or represents an insufficient signal.

A multi-laboratory evaluation of a common in vitro pepsin digestion assay protocol used in assessing the safety of novel proteins

Rationale. Evaluation of the potential allergenicity of proteins derived from genetically modified foods has involved a weight of evidence approach that incorporates an evaluation of protein digestibility in pepsin. Currently, there is no standardized protocol to assess the digestibility of proteins using simulated gastric fluid. Potential variations in assay parameters include: pH, pepsin purity, pepsin to target protein ratio, target protein purity, and method of detection. The objective was to assess the digestibility of a common set of proteins in nine independent laboratories to determine the reproducibility of the assay when performed using a common protocol. Methods. A single lot of each test protein and pepsin was obtained and distributed to each laboratory. The test proteins consisted of Ara h 2 (a peanut conglutin-like protein), beta-lactoglobulin, bovine serum albumin, concanavalin A, horseradish peroxidase, ovalbumin, ovomucoid, phosphinothricin acetyltransferase, ribulose diphosphate carboxylase, and soybean trypsin inhibitor. A ratio of 10U of pepsin activity/microg test protein was selected for all tests (3:1 pepsin to protein, w:w). Digestions were performed at pH 1.2 and 2.0, with sampling at 0.5, 2, 5, 10, 20, 30, and 60min. Protein digestibility was assessed from stained gels following SDS-PAGE of digestion samples and controls. Results. Results were relatively consistent across laboratories for the full-length proteins. The identification of proteolytic fragments was less consistent, being affected by different fixation and staining methods. Overall, assay pH did not influence the time to disappearance of the full-length protein or protein fragments, however, results across laboratories were more consistent at pH 1.2 (91% agreement) than pH 2.0 (77%). Conclusions. These data demonstrate that this common protocol for evaluating the in vitro digestibility of proteins is reproducible and yields consistent results when performed using the same proteins at different laboratories.

Identifying airway sensitizers: cytokine mRNA profiles induced by various anhydrides

Exposure to low molecular weight (LMW) chemicals in the workplace has been linked to a variety of respiratory effects. Within the LMW chemicals, one of the major classes involved in these effects are the acid anhydrides. The immunological basis of respiratory hypersensitivity involves CD4+ cells. By virtue of their induction of cytokines typical of CD4+ T-helper type 2 (Th2) cells-interleukin (IL)-4, 10, and 13-respiratory sensitizers may be identified and differentiated from contact sensitizers which induce Th1 cytokines (IL-2 and IFN-gamma). Our previous work suggested that the ribonuclease protection assay (RPA) was useful in identifying the respiratory sensitizer, trimellitic anhydride (TMA), based on quantitative differences in Th2 cytokine mRNA as compared to the contact sensitizer dinitrochlorobenzene (DNCB). Therefore, the purpose of the studies described in this report was to expand the chemicals tested in the RPA. To this end, four acid anhydrides with known respiratory sensitization potential, TMA, maleic anhydride (MA), phthalic anhydride (PA) and hexahydrophthalic anhydride (HHPA), were tested. Although previously determined to induce immunologically equivalent responses in a local lymph node assay (LLNA), the initial dose chosen (2.5%) failed to induce Th2 cytokine mRNA expression. To determine if the lack of cytokine expression was related to dose, LLNAs were conducted at higher doses for each of the anhydrides. The highest doses evaluated (four- to six-fold higher than those used in the initial RPA) gave equivalent proliferative responses for the various anhydrides and were used for subsequent RPA testing. At these higher doses, significant increases in Th2 versus Th1 cytokine mRNA were observed for all anhydrides tested. These results suggest that the RPA has the potential to serve as a screen for the detection of LMW airway sensitizing chemicals. However, the basis for selecting immunologically equivalent doses may require some modification.

Cytokine profiling for chemical sensitizers: application of the ribonuclease protection assay and effect of dose

Exposure to chemicals in domestic and occupational settings may contribute to increases in asthma and allergy. Airway hypersensitivity (AHS) is T helper-2 (Th2) cell associated, whereas contact hypersensitivity (CHS) is T helper-1 (Th1) cell associated. The distinct cytokine profiles produced by these cells may provide a means of distinguishing respiratory sensitizers from contact sensitizers. In this study, female BALB/c mice were exposed twice on the flanks and three times on the ears using the airway sensitizer trimellitic anhydride (TMA) or the contact sensitizer dinitrochlorobenzene (DNCB). At various times following exposure, total mRNA was extracted from draining lymph node cells and cytokine mRNA profiles analyzed using a multiprobe ribonuclease protection assay (RPA). The Th2 cytokines IL4, IL10, and IL13 were significantly increased in response to TMA compared to DNCB, with optimal detection occurring 14 days following initial exposure. To determine its effect, dose was varied in flank exposures, ear exposures, or both simultaneously. When dose was varied during flank exposures only, TMA induced higher levels of Th2 cytokines than DNCB at all doses tested. DNCB did not induce Th1 cytokines at any dose tested. Variation of TMA dose during both exposures similarly induced Th2 cytokines. Dose only appeared to be a factor when TMA concentration was varied during the ear exposures alone. Thus, these studies suggest that quantitative differences in Th2 responses between TMA and DNCB may be demonstrated over a wide range of doses and these differences may be detected by RPA following dermal exposure to these sensitizers.

Subchronic inhalation toxicity of the chlorinated propane 1,1,1,3,3,3-hexachloropropane (HCC-230fa)

Male and female rats were exposed by inhalation (whole body) to HCC-230fa (1,1,1,3,3,3-hexachloropropane) for 6 h/day, 5 days/week over a 15-week period. Concentrations of 0, 0.50, 2.5, and 25 ppm were studied. A total of eight groups/sex were exposed. Four groups of male and four groups of female rats were used to measure clinical signs and growth, clinical pathology, and tissue pathology. The remaining four groups of male rats were used for immunotoxicological and sperm assessment evaluations, and the remaining four groups of female rats were used for immunotoxicological evaluation. Following the exposure period, surviving male rats were kept for a 1- or 3-month recovery period. Male and female rats exposed to 25 ppm had lower mean body weights, mean body weight gains, and food consumption during the exposure period. Male and female rats exposed to 25 ppm and sacrificed immediately after the exposure period had minimally decreased total leukocyte and lymphocyte counts. These changes were considered to be marginally adverse. Pathologic examination revealed hepatocellular hypertrophy in 0-day recovery males and an increased incidence and/or severity in chronic progressive nephropathy in 0-day, 1-month recovery, and 3-month recovery males at 25 ppm. No other pathological changes, including the testis, epididymis, and other accessory sex organs, were noted in rats during the study. Evaluation of sperm parameters at the end of the exposure period showed statistically significant decreases in epididymal sperm number per cauda epididymis, percent motile sperm, and percent normal sperm morphology at 25 ppm. The biological significance of the slight changes observed in the sperm parameters in the absence of histopathological changes is unclear. After a 1-month recovery period, no biologically significant differences in sperm parameters were noted at 25 ppm compared with controls. Exposure to HCC-230fa did not significantly alter the primary humoral immune response to sheep red blood cell (SRBC). Under the conditions of this study, the no-observed-adverse-effect level (NOAEL) was considered to be 2.5 ppm.

Evaluation of the primary humoral immune response following exposure of male rats to 17beta-estradiol or flutamide for 15 days

There is a concern that certain industrial chemicals found in the environment may mimic or antagonize endogenous hormones and adversely affect the endocrine as well as the immune system. The objective of this study was to determine if exposure of Crl:CD (SD)BR male rats to 17beta-estradiol (17beta-E2), an estrogen receptor agonist, or flutamide (FLUT), an androgen receptor antagonist, would significantly alter the primary IgM humoral immune response to sheep red blood cells (SRBC). This study was conducted in the context of a male in vivo Tier I battery designed to identify endocrine-active compounds (EACs). The Tier I male battery consists of organ weights coupled with a comprehensive hormonal assessment. Rats were dosed by the intraperitoneal route for 15 days with vehicle or 0.001, 0.0025, 0.0075, or 0.050 mg/kg/day 17beta-E2 or 0.25, 1, 5, or 20 mg/kg/day FLUT. Six days prior to termination, selected rats were injected intravenously with SRBC for assessment of humoral immune function. Spleen cell number and spleen and thymus weights were obtained. Serum was analyzed for anti-SRBC IgM antibody by using an enzyme-linked immunosorbent assay. At 0.050 mg/kg/day 17beta-E2, mean final body and absolute thymus weights were significantly decreased to 84 and 65% of control, respectively. 17beta-E2 did not significantly alter spleen weight, spleen cell number, or the primary IgM humoral immune response to SRBC. The no-observed-adverse-effect level (NOAEL) for immune system alteration was 0.050 mg/kg/day 17beta-E2 since the decrease in absolute thymus weight was judged to be secondary to the decrements in body weight. In the Tier I male battery, responses to 17beta-E2 included decreased absolute testis and epididymis weights, decreased relative accessory sex gland unit weights, hormonal alterations (decreased serum testosterone (T), dihydrotestosterone (DHT), and luteinizing hormone (LH), and increased serum prolactin and E2 levels). The lowest-observed-adverse-effect level (LOAEL) for the reproductive indices was 0.001 mg/kg/day 17beta-E2 based on the hormonal alterations seen at this level; no NOAEL was established. Exposure to FLUT did not significantly alter mean final body, spleen, or absolute thymus weights, spleen cell number, or the primary IgM humoral immune response to SRBC. A significant increase (118% of control) in relative thymus weight was observed at 20 mg/kg/day FLUT. The NOAEL for immune system alteration was 5 mg/kg/day FLUT based on the increased relative thymus weights that were judged to be compound-related. In the Tier I male battery, responses to FLUT included decreased absolute epididymis and relative accessory sex gland unit weights and hormonal alterations (increased serum T, DHT, E2, and LH, and decreased follicle stimulating hormone levels). The LOAEL for the reproductive indices was 0.25 mg/kg/day FLUT based on the hormonal alterations seen at this level; no NOAEL was established. Based on these data, the reproductive and not the immune system appears to be the primary target organ of toxicity in young adult male rats treated with either 17beta-E2 or FLUT.

90-day feeding and one-generation reproduction study in Crl:CD BR rats with 17 beta-estradiol

Over the past several years, there has been increasing concern that chemicals and pesticides found in the environment may mimic endogenous estrogens, potentially producing adverse effects in wildlife and human populations. Because estrogenicity is one of the primary concerns, a 90-day/one-generation reproduction study with 17 beta-estradiol was designed to set dose levels for future multigenerational reproduction and combined chronic toxicity/oncogenicity studies. The purpose of these studies is to evaluate the significance of a range of responses as well as to provide benchmark data for a risk assessment for chemicals with estrogen-like activities. This 90-day/one-generation reproduction study was conducted in male and female Crl:CD BR rats using dietary concentrations of 0, 0.05, 2.5, 10, and 50 ppm 17 beta-estradiol. Endpoints were chosen in order to evaluate both subchronic and reproductive toxicity. In addition, several mechanistic/biochemical endpoints were evaluated for their usefulness in follow-up studies. In the P1 generation, dietary administration of 2.5, 10, and 50 ppm 17 beta-estradiol produced dose-dependent decreases in body weight, body weight gain, food consumption, and food efficiency. At 10 and 50 ppm 17 beta-estradiol, minimal to mild nonregenerative anemia, lymphopenia, decreased serum cholesterol (50 ppm only), and altered splenic lymphocyte subtypes were also observed in the P1 generation. Additionally, at these concentrations, there were changes in the weights of several organs. Evidence of ovarian malfunction, characterized by reduced numbers of corpora lutea and large antral follicles, was observed at 2.5 ppm 17 beta-estradiol and above. Other pathologic changes in males and females fed 10 and 50 ppm 17 beta-estradiol included centrilobular hepatocellular hypertrophy; diffuse hyperplasia of the pituitary gland; feminization of the male mammary glands; mammary gland hyperplasia in females; increased number of cystic follicles in the ovary; hypertrophy of the endometrium and endometrial glands in the uterus; degeneration of seminiferous epithelium; and atrophy of the testes and the accessory sex glands. In the reproduction portion of this study, rats fed 10 or 50 ppm 17 beta-estradiol did not produce litters. While there was no evidence that the 50 ppm treated rats mated, 33.3% of the rats fed 10 ppm mated but did not produce litters. No effects on mating and fertility indices were observed in rats fed 0.05 and 2.5 ppm 17 beta-estradiol. Pup weights at birth were statistically decreased relative to control in the groups fed 0.05 and 2.5 ppm 17 beta-estradiol. Weights of the rats in the 0.05 ppm group recovered by postnatal day 4 and remained similar to control throughout the remainder of the study. The mean gestation length of the 0.05 ppm group was slightly, albeit not statistically significantly, shorter (0.5 days) than that of the control group, which may have contributed to the decrease in birth weight of the 0.05 ppm group. In contrast, the weights of the F1 generation rats fed 2.5 ppm 17 beta-estradiol remained decreased relative to the control group throughout the study. Parental administration of 17 beta-estradiol did not alter anogenital distance in male or female pups. The onset of sexual maturation, as measured by day of preputial separation in males and day of vaginal opening in females, was delayed in male rats fed 2.5 ppm (by 8.2 days) and was hastened in female rats fed 0.05 and 2.5 ppm (by 1.6 and 8.8 days, respectively). The age at vaginal opening ranged from 26 to 37, 26 to 35, and 21 to 25 days for rats fed 0, 0.05, and 2.5 ppm 17 beta-estradiol, respectively. Hence, the range of age at vaginal opening was similar between the control and 0.05 ppm group. The organ weight and pathologic alterations observed in the adult F1 generation rats were similar to those observed in the P1 generation rats. (ABSTRACT TRUNCATED)

Assessment of the skin sensitization potential of topical medicaments using the local lymph node assay: an interlaboratory evaluation

The murine local lymph node assay (LLNA) is a method for the predictive identification of chemicals that have a potential to cause skin sensitization. Activity is measured as a function of lymph node cell (LNC) proliferative responses stimulated by topical application of test chemicals. Those chemicals that induce a threefold or greater increase in LNC proliferation compared with concurrent vehicle controls are classified as skin sensitizers. In the present investigations we have evaluated further the reliability and accuracy of the LLNA. In the context of an international interlaboratory trial the sensitization potentials of six materials with a history of use in topical medicaments have been evaluated: benzoyl peroxide, hydroquinone, penicillin G, streptomycin sulfate, ethylenediamine dihydrochloride, and methyl salicylate. Each chemical was analyzed in the LLNA by all five laboratories. Either the standard LLNA protocol or minor modifications of it were used. Benzoyl peroxide and hydroquinone, both human contact allergens, elicited strong LLNA responses in each laboratory. Penicillin G, another material shown previously to cause allergic contact dermatitis in humans, was also positive in all laboratories. Streptomycin sulfate induced equivocal responses, in that this material provoked a positive LLNA response in only one of the five laboratories, and then only at the highest concentration tested. Ethylenediamine dihydrochloride dissolved in a 3:1 mixture of acetone with water, or in 4:1 acetone:olive oil (one laboratory), was uniformly negative. However, limited further testing with the free base of ethylene diamine yielded a positive LLNA response when applied in acetone:olive oil (AOO). Finally, methyl salicylate, a nonsensitizing skin irritant, was negative at all test concentrations in each laboratory. Collectively these data serve to confirm that the local lymph node assay is sufficiently robust to yield equivalent results when performed independently in separate laboratories and indicate also that the LLNA is of value in assessing the skin sensitization potential of topical medicaments.

Further evaluation of the incorporation of an immunotoxicological functional assay for assessing humoral immunity for hazard identification purposes in rats in a standard toxicology study

A previous study (Ladics et al., 1995) conducted in our laboratory using the known immunosuppressant agent, cyclophosphamide, indicated that a functional assay for assessment of humoral immunity may be conducted in rats in a standard toxicology study. The objective of this study was to further examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats in a standard toxicology study using a chemical, carbon tetrachloride (CCl4), whose principal target organ of toxicity is not the immune system. Specifically, the previous study and this study were done to determine whether the conduct of an assay for assessing humoral immune function would affect standard toxicological endpoints. Male CD rats were untreated or dosed orally for 30 or 90 days, excluding weekends, with vehicle or 12.5 or 25 mg/kg CCl4. Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC) for assessment of humoral immune function. One day prior to necropsy, blood for hematological and clinical chemical measurements was collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and later examined microscopically. One-half of each spleen was used to assess spleen cell numbers and quantitate lymphocyte subsets (Thelper; Tcyt/sup; total T- and B-cells) by flow cytometry. Serum was analyzed for anti-SRBC IgM antibody by using an enzyme-linked immunosorbent assay. Administration of 12.5 and 25 mg/kg CCl4 for 30 days decreased SRBC-specific serum IgM levels 42 and 45%, respectively, while 25 mg/kg CCl4 for 90 days increased SRBC-specific IgM levels by 50%. CCl4 did not alter splenic lymphocyte subset numbers nor the weight nor morphology of lymphoid organs. Exposure to 25 mg/kg CCl4 did increase liver weight and serum sorbitol dehydrogenase levels, as well as produce centrilobular fatty change. SRBC administration did not alter any hematological or clinical chemistry parameters, nor lymphocyte subset numbers. With the expected exception of the spleen (slight increase in number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the rather mild hepatotoxic effects of CCL4 exposure observed in this study. Based on these and previous findings, it appears that a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study without altering standard toxicological endpoints.

Assessment of immunotoxicity by multiparameter flow cytometry

Flow cytometry is a unique technology useful in the examination of effects of immunotoxic agents on target cells of the immune system. The purpose of this workshop was to provide an overview of the use of flow cytometry in new and established models of immunotoxicity, with emphasis on the potential applications, assay validation, and potential pitfalls. This overview begins with a discussion of methods useful in the assessment of Ca2+-dependent mechanisms of lymphoid cell activation in surface marker-defined human B cells, T cells, and monocytes. A discussion of the use of flow cytometry in analysis of apoptosis is also presented in this paper. The second paper presents data on the development and use of flow cytometry as an alternative to a Cr51 release assay for an assessment of cytotoxic T cell activation. The use of surface markers for characterizing and distinguishing the effects of chemical irritants from sensitizers is next presented, followed by an overview of the use of fluorescent probes to assess cell thiol status and overall oxidant-induced injury to lymphoid cells. Finally, an interlaboratory study designed to compare and evaluate the use of flow cytometry procedures in rat splenic cell subtyping is presented. Overall, these studies demonstrate the utility of flow cytometry assays in immunotoxicologic research, but further efforts are needed in the validation of many of these assays for routine use in immunotoxicologic testing.

Further evaluation of the local lymph node assay in the final phase of an international collaborative trial

The local lymph node assay (LLNA) is a method used for the prospective identification in mice of chemicals that have the potential to cause skin sensitization. We report here the results of the second and final phase of an international trial in which the performance of the assay has been evaluated using seven test materials in five independent laboratories. The additional chemicals examined here included compounds which are considered less potent allergens than some of those tested in the first phase of the investigation, and includes hexylcinnamic aldehyde (HCA), a chemical recommended by the Organization for Economic Cooperation and Development (OECD) as a positive control for skin sensitization studies. In each laboratory all skin sensitizing chemicals examined (2,4-dinitrochlorobenzene {DNCB}, HCA, oxazolone, isoeugenal and eugenol) elicited positive responses of comparable magnitude as judged by the derived lowest concentration of test chemical required to elicit a 3-fold or greater increase in the proliferative activity of draining lymph node cells compared with vehicle-treated controls. We observed that sodium lauryl sulphate, considered to be a non-sensitizing skin irritant, also induced a positive response in the assay. Para-aminobenzoic acid (pABA), a nonsensitizing chemical, was negative at all test concentrations in each laboratory. Some laboratories incorporated minor modifications into the standard assay procedure, including the evaluation of lymph nodes pooled from individual mice rather than treatment groups and the use of statistical analyses. The use of statistics did not markedly change the determination of the lowest concentration yielding a positive response. These data confirm that the local lymph node assay is robust and yields equivalent results when performed independently.

An international evaluation of the murine local lymph node assay and comparison of modified procedures

The murine local lymph node assay is a predictive test for the identification of skin-sensitizing chemicals. The method has been the subject both of national inter-laboratory studies and of extensive comparisons with guinea pig tests. In the investigations reported here, the local lymph node assay has been evaluated further in the context of an international study comprising five independent laboratories. In addition, the influence of minor modifications to the standard assay procedure on the performance of the test has been examined. The modified procedures investigated were exposure of mice for 4 rather than 3 consecutive days, excision of lymph nodes 4 rather than 5 days after the initiation of exposure and the use of an alternative isotope. All five laboratories, irrespective of whether the standard or a modified protocol was used, were able to identify accurately, and with comparable sensitivity, potassium dichromate and 2,4-dinitrochlorobenzene as skin sensitizers. Using standard criteria, none of the laboratories recorded positive responses with methyl salicylate, a non-sensitizer. In the standard protocol, lymph nodes are pooled for each experimental group and the vigor of responses measured as a stimulation index relative to vehicle controls. A stimulation index of 3 or greater is considered to indicate skin-sensitizing potential. One further modification adopted by three of the laboratories was to analyze nodes from individual animals and, thereby, permit statistical evaluation. This allowed a direct comparison of statistical significance with the conventional stimulation index as criteria for a positive response. The data indicate that, while statistical evaluation may provide, in some instances, for small increases in sensitivity, this may be at the expense of some loss of selectivity. There are, however, insufficient data presently to draw firm conclusions regarding the relative value of statistical analysis. These studies demonstrate that the local lymph node assay is sufficiently robust to accommodate minor procedural and technical modifications without material changes in test performance.

Possible incorporation of an immunotoxicological functional assay for assessing humoral immunity for hazard identification purposes in rats on standard toxicology study

The objective of this study was to examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats on standard toxicology study. Male CD rats were untreated or dosed intraperitoneally daily for 30 or 90 days, excluding weekends, with vehicle or 2 mg/kg cyclophosphamide (CY). Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC). One day prior to necropsy, blood samples for hematological and clinical chemical measurements were collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and examined microscopically. One-half of each spleen was used to prepare a single cell suspension in order to assess spleen cell numbers. Serum was analyzed for anti-SRBC IgM antibody using an enzyme-linked immunosorbent assay. A second set of studies was performed to examine further the effect of SRBC administration on lymphoid organ weights using 30- and 90-day study age-equivalent naive male CD rats. Exposure of animals to 2 mg/kg CY for 30 or 90 days resulted in a 28% and 61% decrease, respectively, in SRBC-specific serum IgM levels. CY treatment also caused mild alterations in some leukocytic parameters, with significant decreases of 35% and 33% in white blood cell and lymphocyte counts, respectively, observed in 30-day CY-treated animals receiving SRBC. Injection of SRBC alone did not alter hematological or clinical chemistry parameters. With the expected exception of the spleen (increased number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the immunosuppressive effects of CY treatment under the conditions of this study. Based on our preliminary findings, a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study.

Evaluation of the humoral immune response of CD rats following a 2-week exposure to the pesticide carbaryl by the oral, dermal, or inhalation routes

The objective of this study was to examine the immunotoxicological effects of the methyl-carbamate pesticide carbaryl via the oral, dermal, or inhalation routes. Male CD rats were exposed to carbaryl 5 d/wk for a 2-wk period. During nose-only inhalation exposures, rats received either 36, 137, or 335 mg/m3 carbaryl in acetone for 6 h. Air only and acetone/air controls were run concurrently. Orally exposed animals received either 1 ml corn oil or 10, 25, or 50 mg/kg carbaryl, while dermally exposed animals received either 2 ml acetone or 100, 500, or 1000 mg/kg carbaryl on their dorsal flank for 6 h. Four days prior to sacrifice, animals from all exposure groups were injected iv with 2 x 10(8) sheep red blood cells (SRBC). The primary immunoglobulin M (IgM) humoral immune response to SRBC was then assessed by measuring SRBC-specific antibody-forming cells (AFC) and levels of serum anti-SRBC IgM antibody, respectively, using the hemolytic plaque assay and an enzyme-linked immunosorbent assay. Individual body weights, spleen, thymus, and liver weights, spleen cell number, and red and white blood cell (RBC, WBC) counts were obtained for each animal. Following nose-only inhalation exposures, dose-dependent decreases in thymus weights, spleen cell number, AFC/spleen, AFC/10(6) splenocytes, and serum levels of SRBC-specific IgM antibody were observed. Significant decreases of 33, 57, and 22% in spleen cell number, AFC/spleen, and thymus weight, respectively, were found at the 335 mg/m3 exposure level. Animals exposed orally to 25 mg/kg carbaryl had a 34% decrease in WBC counts. A 34% decrease in WBC and a 13% increase in RBC counts were observed at the 50 mg/kg oral dose. Significant decreases in liver weights ranging from 11 to 13% were found at all oral exposure levels. Dermal exposure to carbaryl revealed no significant toxicological effects. Results indicate that humoral immune suppression was observed following inhalation, but not following oral or dermal exposures to carbaryl. Immunotoxicological studies evaluating pesticides need to consider relevant exposure routes and dosages for appropriate risk assessment procedures and exposure limits to be established.

Suppression of the murine gut mucosal IgA response to cholera toxin with oral cyclosporine

The gut mucosal immune system may be a primary target for many ingested chemicals. Methods have been developed to examine the effects of chemicals on the systemic humoral immune response; however, studies to evaluate various methods of assessing the local gut mucosal immune response in a toxicology assay have been limited. The objectives of this study were to examine the effects of the known immunosuppressive compound, cyclosporine (CYS), on the generation of a cholera toxin (CT)-specific gut mucosal IgA response and evaluate the methods used to measure the gut IgA response. Groups of female B6C3F1 mice were left untreated or were treated daily, p.o., with corn oil (vehicle) or CYS at doses of 10 and 50 mg/kg for 20 days. On Days 3 and 13, mice were sensitized p.o. with CT. On Day 21, mice were terminated, gut washings were collected, and lamina propria lymphocytes were extracted from gut tissue with collagenase treatment. Cholera toxin-specific IgA in the gut washings was measured by an ELISA. The numbers of CT-specific IgA (CT-IgA) and total IgA antibody-forming cells (spot-forming cells, SFC) obtained from the lamina propria were determined by the ELISPOT method. A dose of 50 mg/kg CYS produced a significant decrease in the amount of CT-IgA in gut washings. This dose also decreased the number of cells recovered from the lamina propria by at least 50%. The amount of CT-specific SFC/million lamina propria cells decreased with a dose of 10 mg/kg CYS, whereas 50 mg/kg CYS did not alter the response.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of benzo[a]pyrene by murine splenic cell types

The objective of the present study was to determine which splenic cell type(s) of B6C3F1 mice was capable of metabolizing B(a)P. Separation of splenocytes based on density by centrifugation through discontinuous Percoll gradients along with immunomagnetic negative selection or antibody-mediated complement lysis was utilized to obtain highly enriched populations of splenocytes for B(a)P metabolism studies. Immunofluorescent cell staining in conjunction with flow cytometry and examination of Giemsa-stained cytospin cell preparations indicated that B- or T-cell populations of greater than 95% purity and an 80-90% pure population of splenic macrophages were routinely attained. Splenic cell populations were incubated with [3H]B(a)P for 24 hr. High-pressure liquid chromatography was used to separate and quantitate the B(a)P metabolites generated by the enriched splenic cell populations. The results of these studies demonstrate that the macrophage is the cell type responsible for the metabolism of B(a)P within the spleen. The major metabolites of B(a)P produced were as follows: an unidentified peak of polar metabolites containing polyhydroxylated metabolites, B(a)P-9,10-dihydroxy-9,10-dihydrodiol, and B(a)P-7,8-dihydroxy-7,8- dihydrodiol. Other splenic cell types examined, including B and T cells, polymorphonuclear cells, or the spleen capsule did not produce amounts of B(a)P metabolites significantly above background levels. Based on these findings, macrophages are the splenic cell types which metabolize B(a)P. As a result, macrophages may be the cell type targeted by B(a)P resulting in suppression of splenic humoral immune responses.

Evaluation of murine splenic cell type metabolism of benzo[a]pyrene and functionality in vitro following repeated in vivo exposure to benzo[a]pyrene

Recent studies have demonstrated that macrophages are the cell types capable of metabolizing benzo[a]pyrene (B(a)P) within the spleens of untreated mice. Since repeated exposure to B(a)P results in immunosuppression and B(a)P is known to induce cytochrome P450 levels, the first objective of this study was to investigate whether exposure of mice to B(a)P could increase the amounts of immunosuppressive B(a)P metabolites generated and/or alter the pattern of B(a)P metabolites formed by several different splenic cell types. Mice were dosed with a daily sc dose of 200 mg/kg B(a)P or vehicle for 4 days. Separation of splenocytes based on density by centrifugation through discontinuous Percoll gradients along with immunomagnetic negative selection or antibody-mediated complement lysis was used to obtain different splenic cell populations. Cells were incubated with [3H]B(a)P for 24 hr. High-pressure liquid chromatography was used to separate and quantitate B(a)P metabolites. Results indicate that splenic macrophages of B(a)P-treated mice produced significantly greater amounts of some metabolites compared to those of vehicle-treated mice. The three major metabolites produced were an unidentified peak of polar metabolites containing polyhydroxylated metabolites, B(a)P-9,10- and B(a)P-7,8-dihydrodiols. Other splenic cell types examined did not produce metabolite amounts significantly above (T-cells, PMNs, or the capsule) or just above (B-cells) background. The second objective was to investigate the splenic cell type(s) targeted by B(a)P resulting in suppression of humoral immunity. Separation-reconstitution studies along with in vitro sensitization techniques with several different antigens (sheep red blood cells (SRBC), dinitrophenyl-Ficoll (DNP-Ficoll), lipopolysaccharide (LPS)) were used to identify splenic target cells following exposure of mice to B(a)P (200 mg/kg/day, sc for 4 days). Findings indicate that in vitro plaque-forming cell (PFC) suppression was due to alterations in the adherent (macrophage) cell population. Exposure also suppressed the PFC response to the T-dependent antigen SRBC and the T-independent antigen DNP-Ficoll, but did not suppress the PFC response to the polyclonal antigen, LPS. These data suggest that B(a)P is targeting macrophages.

Generation of 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene by murine splenic macrophages

Studies have demonstrated that macrophages are the cell types which metabolize benzo[a]pyrene (B[a]P) within the murine spleen. B and T cells, polymorphonuclear cells, or the splenic capsule did not produce amounts of B[a]P metabolites above those of background. Exposure of mice to B[a]P, a known inducer of isozymes of cytochrome P450, resulted in an increase in the amounts of some B[a]P metabolites generated by macrophages. Evaluation of the in vitro plaque-forming-cell response to several T-cell and macrophage-dependent antigens following in vivo exposure to B[a]P indicated that the macrophage is the cell type responsible for B[a]P-induced immunosuppression. While suggestive, the reported data have not definitively established that an enriched splenic macrophage population can generate 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydro-B[a]P (BPDE) from B[a]P-7,8,-dihydroxy-7,8-dihydrodiol (B[a]P-7,8-diol). These data are critical to our hypothesis that the splenic cell type(s) which form BPDE will be the primary target cell responsible for B[a]P-induced immunosuppression. The first objective was to determine if splenic macrophages could generate BPDE. Enriched (80-90% purity) populations of macrophages were incubated with [3H]B[a]P for 24 hr. BPDE generated was quantitated by analysis of the cis- and trans-tetrol hydrolysis products of BPDE via HPLC procedures. Splenic macrophages generated BPDE from B[a]P. The cis syn was the predominate tetrol detected. Exposure of mice to B[a]P increased the amounts of the trans-anti-tetrols 2.2-fold, the trans-syn-tetrols 2.0-fold, the cis-anti-tetrols 1.8-fold, and the cis-syn-tetrols 2.6-fold above those formed by macrophages of vehicle-exposed mice. Both cytochrome P450- and peroxyl radical-dependent pathways are known to oxidize B[a]P-7,8-diol to BPDE. Since macrophages were found to generate BPDE, the second objective was to investigate which enzymatic pathway was responsible for its formation. The B[a]P-(+)-7,8-diol isomer has been shown to produce different specific BPDE isomers via the cytochrome P450 and peroxyl radical pathways. Macrophage populations were incubated with [3H]B[a]P-(+)-7,8-diol for 24 hr and the contribution of the cytochrome P450 and peroxyl radical pathways to BPDE formation determined by detection of syn-BPDE-hydrolysis and anti-BPDE-hydrolysis products, respectively. Based on the ratio of anti/syn BPDE-derived tetrol products, the results demonstrate that splenic macrophages can generate the BPDE by both a cytochrome P450-dependent and -independent (peroxyl radical) pathway. Macrophages are the cells which metabolize B[a]P within the murine spleen and may be the cell type responsible for B[a]P-induced suppression of humoral immune responses.

Suppression of the in vitro humoral immune response of mouse splenocytes by 7,12-dimethylbenz[a]anthracene metabolites and inhibition of immunosuppression by alpha-naphthoflavone

Exposure to 7,12-dimethylbenz[a]anthracene (DMBA) has been demonstrated by numerous investigators to result in suppression of both humoral and cell-mediated immune responses of mice and cultured splenocytes. The mechanism(s) of this DMBA-induced immunosuppression, however, is not well characterized. PAHs must be converted to reactive metabolites via cytochrome P450-dependent monooxygenase systems to exert their carcinogenic and mutagenic effects. Thus, we have hypothesized that immunosuppression seen upon exposure to DMBA may also be mediated by its reactive metabolites. The objective of this study was to determine if DMBA metabolites can suppress the in vitro, T-dependent humoral immune response to sheep red blood cells. Compounds were evaluated in the in vitro plaque-forming cell (PFC) response at concentrations of 10(-9) to 10(-5) M. DMBA and benzo[a]pyrene (B[a]P) were also evaluated for their ability to suppress the in vitro PFC response. Addition of either of these PAHs to splenocyte cultures produced a concentration-dependent suppression of the PFC response, in which B[a]P was found to be 17.5-fold more potent than DMBA. These results are in contrast to those found in vivo, where DMBA has been shown to be more potent than B[a]P at suppressing humoral immunity. The 3,4-diol metabolite of DMBA produced a concentration-dependent suppression (10(-8) to 10(-5) M) of the in vitro PFC response and was found to be 65-fold more potent than the parent compound DMBA. In contrast, the 5,6-diol metabolite of DMBA had no effect on the PFC response or cell viability. Both the 3-OH-DMBA and 7-hydroxymethyl-12-methyl-benz[a]anthracene (7-OHMe-12-Me-BA) metabolites were found to be immunosuppressive at concentrations of 10(-6)M. Furthermore, suppression by 7-OHMe-12-Me-BA was observed at concentrations as low as 10(-8) M. Immunosuppression by the 7-Me-12-OHMe-BA and the di-OHMe-BA metabolites was only observed at high (10(-5) M) concentrations. The cytochrome P450 inhibitor, alpha-naphthoflavone (ANF), was utilized to determine if cytochrome P450-mediated metabolism is involved in DMBA-induced suppression of the in vitro PFC response. ANF (10(-5) M) reversed the DMBA-induced immunosuppression seen at 10(-5) M and attenuated the immunosuppression at 3 x 10(-5) and 10(-4) M. The results of these studies demonstrate that several metabolites of DMBA which can be generated by the cytochrome P450-dependent monooxygenase systems are immunosuppressive in the in vitro PFC response assay. Furthermore, the cytochrome P450 inhibitor, ANF, was able to reverse DMBA-induced immunosuppression.(ABSTRACT TRUNCATED AT 400 WORDS)