Underestimation of specific IgE measurements using extract-based assays on undiluted sera revealed through dilution

An Overview of the Relevance of IgG4 Antibodies in Allergic Disease with a Focus on Food Allergens

Antibodies of the IgG4 isotype are strongly associated with allergic disease but have several properties such as not precipitating with allergens, not activating complement and poor binding to Fcγ receptors that argue against a pro-inflammatory role. In keeping with that, IgG4 antibodies are a striking feature of the response to immunotherapy. In two naturally occurring situations IgG4 antibodies are common with low or absent IgE antibodies. The first example is children raised in a house with a cat and the second is eosinophilic esophagitis (EoE). In many population-based cohorts, the ownership of a cat in early childhood is associated with a decreased prevalence of a cat allergy at age 10. The second example (i.e., EoE) is a novel form of food allergy that is not mediated by IgE and is related to consuming cow’s milk or wheat. In EoE, patients have IgG4 to milk proteins in high > 10 µg/mL or very high > 100 µg/mL titers. Enigmatically these patients are found to have deposits of IgG4 in the wall of their inflamed esophagus. The factors that have given rise to EoE remain unclear; however, changes in food processing over the past 50 years, particularly ultra-heat treatment and the high pressure homogenization of milk, represent a logical hypothesis.

Investigation into the α-Gal Syndrome: Characteristics of 261 Children and Adults Reporting Red Meat Allergy

BACKGROUND

Red meat allergy has historically been understood as a rare disease of atopic children, but the discovery of the "α-Gal syndrome," which relates to IgE to the oligosaccharide galactose-α-1,3-galactose (α-Gal), has challenged that notion.

OBJECTIVE

To describe the clinical and immunologic characteristics of a large group of subjects with self-reported allergy to mammalian meat.

METHODS

This was an observational study of 261 children and adults (range, 5-82 years) who presented for evaluation for allergic reactions to mammalian meat. Results were based on serum assays and a detailed questionnaire.

RESULTS

α-Gal specific IgE ≥ 0.35 IU/mL was detected in 245 subjects and symptom onset occurred ≥2 hours after eating mammalian meat in 211 (81%). Component testing supported a diagnosis of α-Gal syndrome in 95%, pork-cat syndrome in 1.9%, and primary beef allergy in 1.1%. Urticaria was reported by 93%, anaphylaxis by 60%, and gastrointestinal symptoms by 64%. Levels of IgE and IgG specific to α-Gal were similar in subjects who reported early- or delayed-onset symptoms, and in those with and without anaphylaxis. Levels of α-Gal specific IgE and severity of reactions were similar among those with and without traditional atopy, and among children (n = 35) and adults (n = 226). Blood group B trended toward being under-represented among α-Gal-sensitized subjects; however, α-Gal specific IgE titers were high in symptomatic cases with B-antigen.

CONCLUSIONS

The α-Gal syndrome is a regionally common form of food allergy that has a characteristic but not universal delay in symptom onset, includes gastrointestinal symptoms, can develop at any time in life, and is equally common in otherwise nonatopic individuals.

Meat allergy and allergens

IgE-mediated hypersensitivity to ingested animal products, including both mammalian and avian sources, is increasingly appreciated as an important form of food allergy. Traditionally described largely in children, it is now clear that allergy to meat (and animal viscera) impacts both children and adults and represents a heterogeneous group of allergic disorders with multiple distinct syndromes. The recognition of entities such as pork-cat syndrome and delayed anaphylaxis to red meat, i.e- the α-Gal syndrome, have shed light on fundamental, and in some cases newly appreciated, features of allergic disease. These include insights into routes of exposure and mechanisms of sensitization, as well as the realization that IgE-mediated reactions can be delayed by several hours. Here we review mammalian and avian meat allergy with an emphasis on the molecular allergens and pathways that contribute to disease, as well as the role of in vitro IgE testing in diagnosis and management.