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.

Patterns of food hypersensitivity during sixteen years of double-blind, placebo-controlled food challenges.

For 16 years the double-blind, placebo-controlled food challenge (DBPCFC) has been used at the National Jewish Center for Immunology and Respiratory Medicine to determine whether adverse reactions to foods do occur in children. The objective of these studies was to explore these reproducible adverse reactions and to characterize them. Although skin testing was performed on all subjects, a history of an adverse reaction to food and to subsequent DBPCFC were the only criteria for entry into this study. Of 480 children studied, 185 (39%) have had positive DBPCFC results. In these 480 children, 245 (24%) of 1014 DBPCFCs showed positive results. Egg, peanut, and cow milk accounted for 73% of the positive DBPCFC reactions, but many foods produced reactions. Skin test results were positive in most children with a positive DBPCFC reaction, but the large number of patients with asymptomatic hypersensitivity limited the accuracy of a positive skin test result alone as a predictor of clinical symptoms during food ingestion. Evaluation of results in this large number of children for a prolonged period revealed reproducible patterns of symptoms, timing, and incriminated foods. Placebo reactions were rare. The procedure was safe. Twelve youngsters with a negative DBPCFC result subsequently had positive reactions to open challenges when large amounts of the challenge food were used. In each of these cases the reactions were limited to areas of direct contact with the food or could be explained by the larger amount of food ingested during the open challenge. Multiple food hypersensitivity has been a rare finding. The DBPCFC should be the "gold standard" for both research and clinical diagnostic evaluations until it is superseded by methods that have yet to be developed.

The natural history of peanut allergy.

Between 1973 and 1985, 114 children, aged 2 to 14 years, underwent double-blind, placebo-controlled, food challenge (DBPCFC) to peanut. Thirty-two of 46 children with symptoms produced by DBPCFC to peanut were included in this longitudinal evaluation. Contact was made with the 32 subjects 2 to 14 years after their positive DBPCFC to peanut. All 32 subjects had exhibited a positive puncture skin test to peanut at the time of the original evaluation. Sixteen subjects had experienced symptoms caused by accidental peanut ingestion in the year before contact. Eight subjects had reacted to accidental ingestion in more than 1 year but less than 5 years before contact. Eight subjects had completely avoided peanut since the original evaluation and positive DBPCFC. No subjects could be demonstrated to have "outgrown" their peanut reactivity. All subjects tested continued to have skin reactivity to a puncture skin test with peanut extract. It appears uncommon for peanut-sensitive patients to lose their clinical reactivity, even after many years have elapsed. In addition, data were collected concerning reactions to other legumes and other (nonlegume) nuts. Only two patients with DBPCFC to peanut reacted on DBPCFC to soy or pea (one each). None of the subjects with a positive DBPCFC to peanut reacted to nonlegume nuts.

Double-blind, placebo-controlled food challenge (DBPCFC) as an office procedure: a manual.

There is now enough experience with the use of double-blind, placebo-controlled, food challenge (DBPCFC) to recommend its use as an office procedure for most patients complaining of adverse reactions to foods. This manual discusses the practical methods required for the allergist to undertake DBPCFC in the office. Thorough histories supplemented by food allergen skin testing are used to design a DBPCFC that carefully attempts to reproduce the history of food-induced symptoms described by the patient. Precautions that must be taken are delineated before challenge, as is treatment that may be required if a reaction occurs. For those foods to which challenges are positive, longitudinal evaluation with repeated challenge at appropriate intervals help to determine whether or not the problem will resolve over a period of time.

Cottonseed hypersensitivity: new concerns over an old problem.

Seven subjects, who experienced systemic allergic reactions after the ingestion of a newly marketed food supplement, were evaluated to identify the responsible ingredient. Skin testing with extracts prepared from ingredients in the food supplements revealed marked sensitization of all of the subjects to cottonseed protein. Double-blind, placebo-controlled food challenges performed in two subjects with cottonseed flour produced reactions consisting of oropharyngeal pruritus, rhinitis, nausea, diaphoresis, dyspnea, cough, and a fall in pulmonary function tests of 45% or more. All placebo challenges were negative. Because of the reactions observed during these challenges, other subjects were not challenged orally with cottonseed protein but consumed without incident other ingredients in the supplement to which they were skin test positive. Our evaluation strongly incriminates cottonseed protein as the cause of the systemic allergic reactions in these subjects and is consistent with earlier articles in the literature describing the potent allergenicity of cottonseed protein.

Intestinal mucosal mast cells.

Mast cells are unique tissue cells with high affinity surface receptors for IgE and the capacity to synthesize and store histamine in mediator-containing cytoplasmic granules that stain metachromatically upon exposure to cationic dyes. The prominence of mast cells in the gastrointestinal tract and the potential effects of newly generated and preformed mediators released by stimulated mast cells on surrounding gastrointestinal tissues have raised important questions regarding the role of the mast cell in both physiologic and pathophysiologic events in the gut. The elucidation of the role of the mast cell in the gastrointestinal tract is a complex task as illustrated by studies revealing the presence of heterogeneous populations of mast cells in this organ. Morphologic, biochemical, and functional differences have been demonstrated between mast cells located primarily in the mucosa (atypical or mucosal mast cells) and mast cells distributed throughout the connective tissues of the gut (typical or connective tissue mast cells). Awareness of the distinguishing features of mast cell populations in the gut is an important step in unraveling the functional role of gastrointestinal mast cells and may lead to the development of innovative therapeutic approaches to gastrointestinal diseases in which mast cell activation occurs.

Failure of sulfites to produce clinical responses in patients with systemic mastocytosis or recurrent anaphylaxis: results of a single-blind study.

Although sulfite sensitivity can precipitate asthma in a subpopulation of subjects with asthma, its role in precipitating anaphylaxis or as a nonspecific mast cell degranulator in systemic mastocytosis has not been examined. To evaluate critically the importance of sulfites in these diseases, eight patients with systemic mastocytosis and 25 patients with unexplained, recurrent anaphylaxis were challenged in a single-blind fashion; sodium bisulfite in capsules was administered in increasing doses of 1, 5, 10, 25, 50, 100, and 200 mg every 30 minutes. On separate occasions a liquid suspension of 200 mg of sodium bisulfite was administered to one patient with systemic mastocytosis and nine patients with anaphylaxis. Vital signs, pulmonary function tests, plasma histamine levels, and clinical reactions were monitored. There were no observable responses in either the mastocytosis group or in 23 of 25 patients in the anaphylaxis group. Two patients in the anaphylaxis group with initial positive challenges had similar symptoms on subsequent placebo challenge. One subject with asthma and with a history suggestive of sulfite sensitivity responded to oral challenge with 5 mg of sodium bisulfite and 100 micrograms of sodium bisulfite intradermally with a dramatic reduction in FEV, requiring treatment with bronchodilators. A comparison of baseline plasma histamine levels with those obtained after the sulfite challenge procedure in each category demonstrated a significant rise (p less than 0.05) in the systemic mastocytosis group. The overall level of significance determined by applying paired sample t tests to the histamine data from all subjects was p less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and microscopic evidence for the internalization and degradation of heparin-containing mast cell granules by bovine endothelial cells.

Incubation of [35S]heparin-containing mast cell granules with cultured bovine endothelial cells was followed by the appearance of 35S-granule-associated radioactivity within the endothelial cells and a decrease in radioactivity in the extracellular fluid. These changes occurred during the first 24 hours of incubation and suggested ingestion of the mast cell granules by the endothelial cells. Periodic electron microscopic examination of the monolayers confirmed this hypothesis by demonstrating apposition of the granules to the plasmalemma of endothelial cells, which was followed by the engulfment of the granules by cytoplasmic projections. Under light microscopic examination, mast cell granules within endothelial cells then appeared to undergo degradation. The degradation of [35S]heparin in mast cell granules was demonstrated by a decrease in the amount of intracellular [35S]heparin proteoglycan after 24 hours and the appearance of free [35S]sulfate in the extracellular compartment. Intact endothelial cells were more efficient at degrading [35S]heparin than were cell lysates or cell supernatants. These data provide evidence of the ability of endothelial cells to ingest mast cell granules and degrade native heparin that is presented as a part of the mast cell granule.

Evaluation of immediate adverse reactions to foods in adult patients. I. Correlation of demographic, laboratory, and prick skin test data with response to controlled oral food challenge.

Forty-five adult patients, referred to here as the index population, with a history of immediate adverse reactions after food ingestion were evaluated by history, physical examination, laboratory studies, and skin testing. Fifty-six percent of these patients reported adverse reactions to only one food, whereas 84% of the patients reported up to three foods as being capable of eliciting reactions. The average age obtained by history at which adverse reactions began to occur was 19 4/5 yr. The occurrence of these reactions persisted over an average of 14 4/5 yr. Most reactions involved the gastrointestinal tract alone or in combination with the skin or respiratory tract. The most frequently involved foods were shellfish, peanuts, eggs, fish, tomatoes, and walnuts. Twenty-five of the patients participated in oral challenge with the suspected food. The food challenge was positive in 10 patients. Comparison of information obtained by history including personal or family history of any other allergic disease, age of onset of sensitivity, the length of time of suspected sensitivity in years, and the number of foods to which the sensitivity was believed to exist revealed no significant differences between food challenge-positive (FC+) and food challenge-negative (FC-) patients. However, a significant difference in the reaction patterns reported by history in the FC+ and FC- patients was noted in that FC+ patients more often described reactions in which a combination of gastrointestinal, respiratory, and dermatologic symptoms occurred. The complete blood count with differential, blood chemistries, and serum immunoglobulin levels were similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of immediate adverse reactions to foods in adult patients. II. A detailed analysis of reaction patterns during oral food challenge.

Eighty-three oral food challenges were performed on 25 patients with a history of immediate adverse reaction to foods. Seventy-one food challenges were performed in 24 patients, whereas 12 placebos were administered to nine patients. Of the 71 food challenges observed, 12 were positive in 10 patients. All challenges with placebo were negative. Doses of challenge foods provoking observable reactions ranged from 5 to 100 gm. The clinical signs and symptoms noted on food challenge reproduced those reported by history. Reactions were mild, generally self-limited, and were not accompanied by elevations in urinary histamine. A plasma histamine elevation was observed in one patient. A 10- to 12-mo follow-up survey of nine patients with negative food challenges revealed that six patients had resumed eating the challenge food on a regular basis without experiencing adverse reactions, whereas three patients continued to avoid the challenge food. All 10 patients with positive food challenges continued to avoid the challenge food.

Interactions between mast cells, fibroblasts and connective tissue components.

It has long been recognized that mast cells occur throughout connective tissues. Histologic studies have revealed that such cells release their granules into the surrounding environment upon exposure to both immunologic and nonimmunologic stimuli. By microscopy these extracellular granules appeared to be phagocytosed by fibroblasts and by blood-borne phagocytic cells as they entered the site of mast cell degranulation. Such in vivo observations led to the suggestion that mast cells both altered connective tissue components and influenced fibroblast function through these discharged granules. Recent in vitro studies using cultured fibroblasts and isolated mast cells and mast cell granules have confirmed both these hypotheses. In addition, such studies have also documented that fibroblasts degrade ingested mast cell granules. Such studies document that a number of critical interactions may occur between mast cells and connective tissue components.

Degradation of the heparin matrix of mast cell granules by cultured fibroblasts.

The ability of cultured rat fibroblasts to phagocytose rat peritoneal mast cell granules has been previously demonstrated by light and electron microscopy. To determine if the heparin matrix of ingested granules could be degraded by fibroblasts after phagocytosis, the heparin within peritoneal mast cells was labeled with [35S]sulfate in vivo. The 35S-labeled rat peritoneal mast cells were purified and their granules were isolated and shown to contain [35S]heparin proteoglycan. Incubation of [35S]heparin proteoglycan-containing granules with cultured rat fibroblasts revealed internalization of radioactivity by the fibroblasts over the first 24 hr consistent with phagocytosis of the granules by these fibroblasts. The [35S]heparin proteoglycan internalized by the fibroblasts was shown to decrease in size over 72 hr indicating that the fibroblasts were capable of degrading the heparin within the ingested granules. Degradation of [35S]heparin proteoglycan within the fibroblast was accompanied by the appearance of free [35S]sulfate in the extracellular compartment. Similar findings were obtained using cultured human fibroblasts. These data demonstrate for the first time that both rat and human fibroblasts are not only capable of ingesting mast cell granules but also of degrading mast cell granule heparin proteoglycan. This ingestion and degradation of mast cell granules by fibroblasts may represent an important mechanism in the regulation of the biologic expression of heparin and other granule-associated mediators in immediate hypersensitivity reactions.