Early-life gut microbiome and egg allergy.

BACKGROUND: Gut microbiota may play a role in egg allergy. We sought to examine the association between early-life gut microbiota and egg allergy. METHODS: We studied 141 children with egg allergy and controls from the multicenter Consortium of Food Allergy Research study. At enrollment (age 3 to 16 months), fecal samples were collected, and clinical evaluation, egg-specific IgE measurement, and egg skin prick test were performed. Gut microbiome was profiled by 16S rRNA sequencing. Analyses for the primary outcome of egg allergy at enrollment, and the secondary outcomes of egg sensitization at enrollment and resolution of egg allergy by age 8 years, were performed using Quantitative Insights into Microbial Ecology, Phylogenetic Investigation of Communities by Reconstruction of Unobserved States, and Statistical Analysis of Metagenomic Profiles. RESULTS: Compared to controls, increased alpha diversity and distinct taxa (PERMANOVA P = 5.0 × 10-4 ) characterized the early-life gut microbiome of children with egg allergy. Genera from the Lachnospiraceae, Streptococcaceae, and Leuconostocaceae families were differentially abundant in children with egg allergy. Predicted metagenome functional analyses showed differential purine metabolism by the gut microbiota of egg-allergic subjects (Kruskal-Wallis Padj  = 0.021). Greater gut microbiome diversity and genera from Lachnospiraceae and Ruminococcaceae were associated with egg sensitization (PERMANOVA P = 5.0 × 10-4 ). Among those with egg allergy, there was no association between early-life gut microbiota and egg allergy resolution by age 8 years. CONCLUSION: The distinct early-life gut microbiota in egg-allergic and egg-sensitized children identified by our study may point to targets for preventive or therapeutic intervention.

Integrative transcriptomic analysis reveals key drivers of acute peanut allergic reactions.

Mechanisms driving acute food allergic reactions have not been fully characterized. We profile the dynamic transcriptome of acute peanut allergic reactions using serial peripheral blood samples obtained from 19 children before, during, and after randomized, double-blind, placebo-controlled oral challenges to peanut. We identify genes with changes in expression triggered by peanut, but not placebo, during acute peanut allergic reactions. Network analysis reveals that these genes comprise coexpression networks for acute-phase response and pro-inflammatory processes. Key driver analysis identifies six genes (LTB4R, PADI4, IL1R2, PPP1R3D, KLHL2, and ECHDC3) predicted to causally modulate the state of coregulated networks in response to peanut. Leukocyte deconvolution analysis identifies changes in neutrophil, naive CD4+ T cell, and macrophage populations during peanut challenge. Analyses in 21 additional peanut allergic subjects replicate major findings. These results highlight key genes, biological processes, and cell types that can be targeted for mechanistic study and therapeutic targeting of peanut allergy.

Component-resolved analysis of IgA, IgE, and IgG4 during egg OIT identifies markers associated with sustained unresponsiveness.

BACKGROUND: In a previously reported CoFAR study, 55 subjects with egg allergy underwent randomized, placebo-controlled egg oral immunotherapy (eOIT). Active treatment induced desensitization in most and sustained unresponsiveness (SU) in a smaller subset. We hypothesized that component-resolved analysis of IgE, IgG4, IgA, IgA1, and IgA2 may identify potential biomarkers of SU in OIT subjects. METHODS: Longitudinal samples for 51 egg-allergic subjects (37 active and 14 placebo) were available. Egg white (EW)-, ovalbumin (OVA)-, and ovomucoid (OVM)-specific levels of IgA, IgA1, and IgA2 were quantified by ELISA. IgE and IgG4 to these antigens were quantified using ImmunoCAP® . Clinical responders achieved SU to egg; all others were considered nonresponders. Between-group comparisons were made among active and placebo, as well as responders and nonresponders. RESULTS: No placebo subjects achieved responder status. Through month 48, among the 37 active subjects, baseline IgE-OVM was lower in responders (median 3.97 kU/l, n = 19) than in nonresponders (10.9 kU/l, n = 18, P = 0.010). Logistic regression analysis revealed that lower baseline IgE-EW (P = 0.038), IgE-OVM (P = 0.032), and a higher IgG4/IgE-OVM ratio (P = 0.013) were associated with clinical response. Relative increases in IgG4-EW, IgA-EW, and IgA2-EW were observed in responders (P = 0.024, 0.024, and 0.029, respectively). IgG4/IgE, IgA/IgE, and IgA2/IgE ratios for EW and IgA/IgE ratio for OVA were found to be significantly elevated among responders (P = 0.004, 0.009, 0.028, and 0.008, respectively). CONCLUSIONS: Increased IgG4-EW, IgA-EW, and IgA2-EW during eOIT are associated with clinical response to eOIT. Lower pretreatment IgE-EW and IgE-OVM are also associated with SU. Future studies are needed to evaluate and validate these potential biomarkers.

Utility of component analyses in subjects undergoing sublingual immunotherapy for peanut allergy.

BACKGROUND: Sublingual immunotherapy (SLIT) with peanut changes clinical and immune responses in most peanut-allergic individuals, but the response is highly variable. OBJECTIVE: We sought to examine the component-specific effects of peanut SLIT and determine whether peanut component testing could predict the outcome of a double-blind, placebo-controlled food challenge (DBPCFC) after 12 months of peanut SLIT. METHODS: We included 33 subjects who underwent peanut SLIT with a DBPCFC of 2500 mg of peanut protein performed after 12 months of therapy. Plasma samples from baseline and after 12 months of peanut SLIT were assayed using ImmunoCAP for IgE and IgG4 against whole peanut, Ara h 1, Ara h 2, Ara h 3, Ara h 8, and Ara h 9. RESULTS: Following 12 months of SLIT, 10 subjects (30%) passed the DBPCFC without symptoms and were considered desensitized. Subjects that failed the DBPCFC tolerated a median of 460 mg peanut protein (range: 10-1710 mg). The desensitized group had significantly lower baseline levels of IgE against peanut (median 40.8 vs. 231 kUA /L, P = 0.0082), Ara h 2 (median 17 vs. 113 kUA /L, P = 0.0082), and Ara h 3 (median 0.3 vs. 8.5 kUA /L, P = 0.0396). ROC curves indicated that baseline IgE against peanut and Ara h 2 were equally effective at discriminating between the two groups (AUC = 0.7957, P = 0.007752 for both). CONCLUSION AND CLINICAL RELEVANCE: In this cohort of subjects undergoing SLIT for peanut allergy, lower baseline levels of IgE against Ara h 2, Ara h 3, and peanut were associated with successful desensitization.

Effects of a pre-existing food allergy on the oral introduction of food proteins: findings from a murine model.

Cashew-allergic mice develop elevated walnut-specific IgE upon oral feeding of walnut proteins. Ingestion of tree nuts in the presence of a known nut allergy could lead to additional sensitizations and anaphylaxis following subsequent exposure.

A phase 1 study of heat/phenol-killed, E. coli-encapsulated, recombinant modified peanut proteins Ara h 1, Ara h 2, and Ara h 3 (EMP-123) for the treatment of peanut allergy.

BACKGROUND: Immunotherapy for peanut allergy may be limited by the risk of adverse reactions. OBJECTIVE: To investigate the safety and immunologic effects of a vaccine containing modified peanut proteins. METHODS: This was a phase 1 trial of EMP-123, a rectally administered suspension of recombinant Ara h 1, Ara h 2, and Ara h 3, modified by amino acid substitutions at major IgE-binding epitopes, encapsulated in heat/phenol-killed E. coli. Five healthy adults were treated with 4 weekly escalating doses after which 10 peanut-allergic adults received weekly dose escalations over 10 weeks from 10 mcg to 3063 mcg, followed by three biweekly doses of 3063 mcg. RESULTS: There were no significant adverse effects in the healthy volunteers. Of the 10 peanut-allergic subjects [4 with intermittent asthma, median peanut IgE 33.3 kUA /l (7.2-120.2), and median peanut skin prick test wheal 11.3 mm (6.5-18)]; four experienced no symptoms; one had mild rectal symptoms; and the remaining five experienced adverse reactions preventing completion of dosing. Two were categorized as mild, but the remaining three were more severe, including one moderate reaction and two anaphylactic reactions. Baseline peanut IgE was significantly higher in the five reactive subjects (median 82.4 vs 17.2 kUA /l, P = 0.032), as was baseline anti-Ara h 2 IgE (43.3 versus 8.3, P = 0.036). Peanut skin test titration and basophil activation (at a single dilution) were significantly reduced after treatment, but no significant changes were detected for total IgE, peanut IgE, or peanut IgG4. CONCLUSIONS: Rectal administration of EMP-123 resulted in frequent adverse reactions, including severe allergic reactions in 20%.

Immunology in the Clinic Review Series; focus on allergies: immunotherapy for food allergy.

There is no approved therapy for food allergy. The current standard of care is elimination of the triggering food from the diet and accessibility to epinephrine. Immunotherapy is a promising treatment approach. While desensitization to most foods seems feasible, it remains unclear if a permanent state of tolerance is achievable. The research team at Duke is pioneering immunotherapy for food allergies. Work here has evolved over time from small open-label pilot studies to larger randomized designs. Our data show that immunological changes associated with immunotherapy include reduction in mast cell reactivity, decreased basophil responses, decreased specific-immunoglobulin (Ig)E, increased IgG4 and induction of regulatory T cells. Immunotherapy has generated much excitement in the food allergy community; however, further studies are needed before it is ready for clinical use.

How do we know when peanut and tree nut allergy have resolved, and how do we keep it resolved?

Over the last two decades, the prevalence of peanut and tree nut allergy has increased throughout the western world. Adverse reactions to these foods account for over 50% of all deaths resulting from food-related anaphylaxis. Until recently, evidence suggested that all peanut and tree nut allergy were permanent. It is now known that about 20% and 10%, respectively, of young patients outgrow peanut and tree nut allergies. Achieving tolerance is associated with increasing circulating T regulatory cells and reduced production of allergen-specific IgE. Reliable predictors of resolution are not yet available. A direct correlation between skin test weal size and allergen-specific IgE, at the time of diagnosis and likelihood of resolution, has been reported. Resolution of peanut or tree nut allergy cannot be determined conclusively by either allergen-specific IgE analysis or by skin prick testing. Oral food challenge is the gold standard for determining resolution of food allergy. Food challenges should only be undertaken in a clinical setting fully equipped to deal with a potential severe adverse reaction. Approximately 8% of patients who outgrow peanut allergy may suffer a recurrence, but recurrent tree nut allergy has not been reported to date. Infrequent ingestion of peanut may be related to the re-emergence of allergy. Induction of tolerance through oral immunotherapy or sublingual immunotherapy is now being actively studied, but remains experimental. Studies have reported short-term desensitization to peanut, but ongoing follow-up will determine whether tolerance is achieved long term.

Pediatric food allergy and mucosal tolerance.

The gastrointestinal (GI) mucosal immune response is characterized by an intricate balance between host defense and immunoregulation. A principal element of this normal response is acquisition of oral tolerance. Aberrations in oral tolerance induction can lead to food allergy, an increasingly prevalent disorder that causes significant medical and psychosocial stressors for patients and families. At present there is no definitive therapy for food allergy and the mainstays of treatment are allergen avoidance, nutritional support, and ready access to emergency medications. Significant progress toward an active therapy for food allergy has been made with the advent of novel therapies such as oral immunotherapy (OIT) and sublingual immunotherapy (SLIT), which modulate the GI mucosal immune response with the goal of promoting oral tolerance. In this review, we will examine the mechanisms of oral tolerance induction and its relation to food allergy and explore novel immunotherapeutic strategies for treatment and prevention of food allergy.

Food allergy QoL questionnaire for children aged 0-12 years: content, construct, and cross-cultural validity.

BACKGROUND: To date, there is no food allergy-specific questionnaire that allows parents to report children's health-related QoL (HRQL) from the child's perspective. OBJECTIVE: The aim of this study was to develop a sensitive, multi-dimensional measure to assess parental perception of HRQL in children aged 0-12 years with food allergy. METHODS: The Food Allergy QoL - Parent Form (FAQLQ-PF) was developed and validated in four stages: (1) item generation using focus groups, expert opinion, and literature review; (2) item reduction, using clinical impact and factor analysis; (3) internal and test-retest reliability and construct validity were evaluated using relevant scales of the Child Health Questionnaire (CHQ)-28 and the disease-specific food allergy independent measure (FAIM); and (4) cross-cultural and content validity was examined by administering the questionnaire in a US sample. RESULTS: Stage 1: Saturation was reached at 110 items. Stage 2: The reduced instrument has 14 items for children <4 years and 26 and 30 items for children aged 4-6 years and 7-12 years, respectively. Factor analysis revealed three subscales: emotional impact, food anxiety, and social and dietary limitations, accounting for 68% of the variance. Stage 3: Cronbach's alpha >0.7 for subscales and total score. Construct validity was demonstrated by significant correlations between relevant scales of the CHQ-28 and FAQLQ-PF subscales (r=0.69-0.77, P<0.01), and between FAQLQ-PF subscales and the FAIM. Sensitivity was shown by significant within-group differences in a sample of 124 food-allergic children. Stage 4: The FAQLQ-PF was validated in a sample of US children, Cronbach's alpha >0.7 for subscales and total score. Construct validity was demonstrated by significant correlations between FAQLQ-PF and the FAIM (parent report) and between the FAQLQ-PF and the FAIM (child report). No differences were observed between the US and Irish scores. CONCLUSION: The FAQLQ-PF is psychometrically robust, with excellent reliability and validity.

Contribution of Ara h 2 to peanut-specific, immunoglobulin E-mediated, cell activation.

BACKGROUND: Ara h 2 is a potent peanut allergen but its contribution to the ability of a crude peanut extract (CPE) to cross-link IgE and activate mast cells has not been rigorously evaluated. OBJECTIVE: To measure the contribution that Ara h 2 makes to the effector function of a CPE. METHODS: Ara h 2 was specifically removed from a CPE as demonstrated by immunoblots, 2D gels, and an inhibitory ELISA. Functional assays of sham-treated and Ara h 2-depleted CPEs were performed with RBL SX-38 cells sensitized with IgE from highly peanut-allergic subjects and with naturally sensitized basophils. RESULTS: Depletion of approximately 99% of the Ara h 2 from the CPE led to an increase in the concentration of the CPE necessary to give 50% of maximal degranulation (EC50) of the SX-38 cells following sensitization with sera that contain anti-Ara h 2 IgE. Assays with a pool of 10 sera showed a small but significant increase in the EC50 following depletion of Ara h 2 (1.65+/-0.15-fold; P<0.05) and assays of seven individual sera showed a similar increase in the average EC50 (1.7+/-0.2-fold; P<0.02). The percent of the anti-peanut IgE that binds Ara h 2 correlated with an increase in the EC50 of the CPE following depletion of Ara h 2 (r=0.83; P<0.02). On the other hand, data from three of these patients studied with a basophil histamine release assay did not show a significant effect of depletion of Ara h 2. CONCLUSION: Based on its ability to cross-link IgE effectively, Ara h 2 is clearly an important peanut allergen. Its ability to cross-link IgE effectively from a specific serum is related to the proportion of anti-Ara h 2 in that serum but Ara h 2 does not account for a majority of the effector activity of the CPE for any of the sera studied.

Lack of immunogenicity of ice structuring protein type III HPLC12 preparation administered by the oral route to human volunteers.

Before a novel protein can be used in foods, its potential allergenicity must be assessed. In this study, healthy volunteers consumed ice structuring protein (ISP) Type III preparation or a control material 5 days a week for a total of 8 weeks. General measures of health were recorded during the study, and the immunogenicity of the protein was assessed by monitoring the levels of IgG and IgE antibodies specific for ISP Type III. The participants remained in good health throughout the study and during the 4 week follow-up period. No IgG or IgE antibodies specific for ISP Type III were detected in the blood of the participants. Investigations of immunogenicity in man have not been previously applied in the context of safety evaluation and they do not form part of the regimens proposed for the evaluation of protein allergenicity. Consequently no standardised protocols exist for such studies, nor any background against which to interpret the results. Nevertheless, the absence of an immune response using a protocol which could have been expected to result in a response with a strongly immunogenic protein, confirms the conclusions of earlier published work, and attests to the lack of allergenicity of ISP Type III preparation.

A consensus protocol for the determination of the threshold doses for allergenic foods: how much is too much?

BACKGROUND: While the ingestion of small amounts of an offending food can elicit adverse reactions in individuals with IgE-mediated food allergies, little information is known regarding these threshold doses for specific allergenic foods. While low-dose challenge trials have been conducted on an appreciable number of allergic individuals, a variety of different clinical protocols were used making the estimation of the threshold dose very difficult. OBJECTIVE: A roundtable conference was convened to develop a consensus clinical protocol for low-dose challenge trials for the estimation of threshold doses for specific allergenic foods. METHODS: In May 2002, 20 clinical allergists and other interested parties were invited to participate in a roundtable conference to develop consensus of the key elements of a clinical protocol for low-dose challenge trials. RESULTS: A consensus protocol was developed. Patients with convincing histories of food allergies and supporting diagnostic evidence including past challenge trials or high CAP-RAST scores can be enrolled in low-dose challenge trials. Care must be taken with younger patients to assure that they have not outgrown their food allergy. An approach was developed for the medication status of patients entering such trials. Challenge materials must be standardized, for example, partially defatted peanut flour composed of equal amounts of the three major varieties of peanuts (Florunner, Virginia, Spanish). Challenge materials must be appropriately blinded with sensory evaluation used to confirm the adequacy of blinding. A double-blind, placebo-controlled design should be used for low-dose challenge trials. Low-dose challenge trials would begin at doses of 10 microg of the allergenic food and would continue with doses of 100 microg and 1 mg followed by specific higher doses up to 100 mg depending upon the expert judgement of the physician; even higher doses might be applied to assure that the patient is indeed reactive to the particular food. A 30-min time interval would be used between doses, and reactive doses would be expressed as both discrete and cumulative doses. The goal of each challenge would be to develop objective symptoms; trials should not be discontinued on the basis of subjective symptoms only. Statistically, a minimum of 29 patients would be enrolled in low-dose challenge trials for each allergenic food because 0 reactors out of 29 patients at a particular dose allow the conclusion that there is 95% certainty that 90% of allergic individuals will not react to that dose. CONCLUSION: A consensus protocol was developed. Using this protocol, it will be possible to estimate threshold doses for allergenic foods, the lowest amount that elicits mild, objective symptoms in highly sensitive individuals.

Serological characteristics of peanut allergy in children.

BACKGROUND: Food challenge is considered an excellent clinical tool for the diagnosis of specific food allergy. However in the case of peanut allergy it may be difficult to perform because of the severity of the reactions. The quantitation of a specific immunoglobulin E (IgE) response to different peanut allergens could also contribute to the improvement of the diagnosis. We characterized the IgE response to a whole peanut protein extract and to Ara h 1 and Ara h 2 in different groups of patients classified according to the severity of their allergic reactions. METHODS: Specific serum IgE were analyzed in 96 children by enzyme-linked immunosorbent assay tests using a whole protein extract or purified peanut proteins and anti-human IgE monoclonal antibodies labeled with acetylcholinesterase. RESULTS: A parallel was observed between levels of peanut-specific IgE and the classification in five groups and subgroups of patients upon increasing severity of symptoms, especially within the group of highest severity. Moreover, the highest frequency of positive response and the highest levels of specific IgE were observed with whole peanut protein extract. CONCLUSION: In a retrospective evaluation of peanut allergy in children, we have shown that quantitation of peanut-specific IgE could be used to avoid a food challenge particularly in the case of severe reactions. When compared to Ara h 1 and Ara h 2, whole peanut protein extract appeared to be the most appropriate allergen to perform the test.

Oral administration of IL-12 suppresses anaphylactic reactions in a murine model of peanut hypersensitivity.

There is no satisfactory therapeutic intervention for peanut allergy, which accounts for most life-threatening food allergic reactions. Since IL-12 has been found to inhibit allergic airway responses in a mouse model of asthma and to cure Th2 cytokine-mediated murine schistosomiasis, we hypothesized that IL-12 treatment might also inhibit peanut allergic reactions. Consequently, we investigated the effects of oral IL-12 treatment in a murine model of peanut allergy and found that oral administration of liposome encapsulated rIL-12 could both prevent and reverse peanut hypersensitivity and could reduce histamine release, peanut-specific serum IgE and IgG1, and fecal IgA levels. Oral IL-12 treatment also increased IFN-gamma but did not decrease IL-4 or IL-5 levels. We conclude that oral rIL-12 treatment has therapeutic as well as preventive effects on peanut allergy, which are associated with increased IFN-gamma production.

Randomized, double-blind, placebo-controlled, food allergy challenge to olestra snacks.

Following approval of the fat replacer olestra for use in preparing savory snacks, Procter & Gamble implemented a postmarketing surveillance program to monitor marketplace introduction. Three and one-half percent of all health effects reported by consumers to the surveillance toll-free number were allergy-type symptoms (e.g., rash, itching, edema, hives, dyspnea). Because of these reports, we investigated whether olestra or some component of olestra snacks was a likely allergen in some subset of the population. A single center, randomized, double-blind, placebo-controlled, within-subject crossover food challenge study was conducted to confirm or refute the allergenicity of olestra snacks. Of the 65 subjects who reported symptoms consistent with immediate hypersensitivity to olestra's postmarketing surveillance program, 14 men and women traveled to the Arkansas Children's Hospital Research Institute to participate in this study. Each subject underwent a standard skin prick test at the beginning of the study, to help determine what component, if any, of the olestra product was allergenic. Following the skin prick test, subjects ate in random order, olestra-containing potato chips and regular fat-containing potato chips. The dose of potato chips consumed at each challenge was at least the amount alleged to have caused the symptoms that prompted the consumer to phone the postmarketing surveillance toll-free number. No subject experienced an allergic reaction after consuming the olestra-containing chips. Nor did any subject elicit a positive response to olestra following the skin prick testing. Two subjects had positive reactions consistent with immediate hypersensitivity after consuming the regular-fat, placebo potato chips. The results of this study confirm that olestra is unlikely to have an allergenic potential.

Randomized clinical trial of soy formula with and without added fiber in antibiotic-induced diarrhea.

OBJECTIVE: The objective of this study was to examine the effects of soy formulas with and without added soy fiber in children who developed diarrhea while receiving antibiotics. DESIGN: In a masked, randomized parallel study, older infants and toddlers were fed commercial soy formulas with or without added soy fiber for 10 days on occurrence of diarrhea during the administration of antibiotics. Subjects were stratified by feeding (formula versus cow's milk). The primary variables were duration of diarrhea, stool characteristics, and intake. Secondary variables were weight and spit-up. RESULTS: All 45 children who completed the 10-day study received >30% of their caloric intake from formula. Fiber intake from other foods did not differ between groups and averaged 0.5 g/day. Total median fiber intake of the group fed the formula with added fiber was 6.53 g/day. The mean duration of diarrhea was 25.1 +/- 5.2 hours for children fed the formula with added fiber and 51.6 +/- 10.7 hours for those fed the regular formula (P =.0013). CONCLUSION: The duration of antibiotic-induced diarrhea in children fed the soy formula with added soy fiber was significantly reduced.

A voluntary registry for peanut and tree nut allergy: characteristics of the first 5149 registrants.

BACKGROUND: A voluntary registry of individuals with peanut and/or tree nut allergy was established in 1997 to learn more about these food allergies. OBJECTIVE: The purpose of this study was to elucidate a variety of features of peanut and tree nut allergy among the first 5149 registry participants. METHODS: The registry was established through use of a structured questionnaire distributed to all members of the Food Allergy and Anaphylaxis Network and to patients by allergists. Parental surrogates completed the forms for children under the age of 18 years. RESULTS: Registrants were primarily children (89% of registrants were younger than 18 years of age; the median age was 5 years), reflecting the membership of the Network. Isolated peanut allergy was reported by 3482 registrants (68%), isolated tree nut allergy by 464 (9%), and allergy to both foods by 1203 (23%). Registrants were more likely to have been born in October, November, or December (odds ratio, 1.2; 95% CI, 1.18-1.23; P <.0001). The median age of reaction to peanut was 14 months, and the median age of reaction to tree nuts was 36 months; these represented the first known exposure for 74% and 68% of registrants, respectively. One half of the reactions involved more than 1 organ system, and more than 75% required treatment, frequently from medical personnel. Registrants with asthma were more likely than those without asthma to have severe reactions (33% vs 21%; P <.0001). In comparison with initial reactions, subsequent reactions due to accidental ingestion were more severe, more common outside the home, and more likely to be treated with epinephrine. CONCLUSIONS: Allergic reactions to peanut and tree nut are frequently severe, often occur on the first known exposure, and can become more severe over time.

Evaluation of immune parameters in propanil-exposed farm families.

The rice herbicide propanil induces alterations in the mouse immune system, causing significant decreases in T cell-dependent and T cell-independent antibody responses. This postemergent herbicide is used extensively in rice production in the Mississippi River delta region of the southern United States. The aerial application and airborne drift of propanil may pose health concerns to exposed farm families living adjacent to sprayed rice fields. To determine if aerial spraying of propanil increases risks of altered immune responses in families bordering rice fields, immune parameters were assessed during a 2-year study. Families living within 100 yards of rice fields were compared in a case control study to farm families whose homes exceeded 1 mile from any rice field. Blood was analyzed in adults (n = 56) and children (n = 52) at three time intervals: (1) preseason, prior to propanil application; (2) 5-7 days after aerial application of propanil to rice fields; and (3) postseason, following harvest. Exposed adults and children were compared with controls for a number of immune parameters. Total cell count and the percentage of various lymphocytes (T cells, B cells, CD4+ helper cells, and CD8+ suppressor cells) and natural killer (NK) cells, mitogen-induced cell proliferation, cytokine (IL-2+) production, and NK cell function were assessed. A comparison of immune function between exposed and nonexposed farm families showed no significant differences, possibly related to propanil exposure. However, some immune test parameters changed as a function of season rather than propanil exposure. The data indicate that individuals living next to rice fields are not at increased risk of altered immune function due to propanil exposure.