Egg

1. Major Allergens

     Ovomucoid:     Ovomucoid (Gal d 1) is a glycoprotein with a molecular weight of 28 kDa, a pI of 4.0, and exhibits trypsin inhibitor activity. It contains no tryptophan, which is found in most other egg white proteins. There are three tandem domains, each of which is homologous to pancreatic secretory trypsin inhibitor, and each acts as a native globular protein. Its predicted secondary structure indicates some α-helical and β-structural elements, and polymorphism of the protein exist. Ovomucoid has a major allergen. For example, in one study, 48 of 68 sera samples from egg-sensitive patients had positive crossed radioimmunoelectrophoresis (CRIE) to ovomucoid, whereas in a similar study, 21 of 34 sera samples from egg-allergic patients had positive RAST and CRIE to ovomucoid. However, Bernhisel-Broadbent et al. suggested that the use of commercially purified ovalbumin has led to the erroneous concept of ovalbumin as a major egg allergen, because ovomucoid was found to have contaminated commercial ovalbumin preparations (less than 1%). In this study, ovomucoid was found to be a more potent allergen than purified ovalbumin by skin testing (ST) and RAST in 18 children with egg allergy.

      Ovalbumin:     Ovalbumin (Gad d 2) is a monomeric phosphoglycoprotein with a molecular weight of 43 to 45 kDa and a pI of 4.5. The 385 amino acid sequence has been established. Purified ovalbumin has three variants: A1, A2, and A3, which contain two , one, and no phosphate groups per molecule, respectively. The susceptibility to denaturation increases in order of decreasing degree of phosphorylation. The mRNA nucleotide sequence of ovalbumin has been reported.

      Ovalbumin has been documented in several studies as a major allergen. For example, 68 of 68 sera from egg-sensitive patients were positive in CRIE to ovalbumin in one study, whereas in a similar study, 34 of 34 sera from egg-allergic patients were positive in RAST and CRIE to ovalbumin.

      Ovotranferrin (conalbumin):    Ovotransfrrin (Gal d 3) has a molecualr weight of 77 kDa, and a pI of 6.0. Its 686 amino acid residues and sequence have been identified directly and deduced indirectly by mRNA sequencing. It has antimicrobial activity and iron-binding properties. Ovotransferrin has also been documented in several studies as a major egg allergen.For example, in one study,35 of 68 serafrom eggsensitive patients had positive CRIE to ovotransferrin, whereas in a similar study, 20 of 34 sera from egg-allergic patients had positive RAST and CRIE to ovotransferrin.

      Apovitellins:     Apovitellins derived from the low-density lipoprotein of the egg yolk are major allergens for some egg-sensitive individuals. Apovitellin I has been shown to be a major allergen in RAST studies using sera from egg-sensitive individuals. Apovitellin VI was found to be a major allergen in RAST analysis in a study by Walsh et al. Anet et al. discovered that the apovitellins III, V, and VI were minor allergens for the individuals in their study.

2. minor allergens

      Lysozyme - lysozyme (Gal d 4) is a 14.3-kDa protein with a pI of 10.7. Its 129 amino acids have been sequenced. It is a single polypeptide chain cross-linked by four disulfide bridges. The chain is folded upon itself so that the first 49 residues from the N-teminal end form a compact globular domain. There is a second hydrophilic domain(residues 40 to 85) that foms one site of the active site cleft. Its mRNA with exons and flanking introns have also been dentified, The role of lysozyme in egg allergy has not been established. Miller amd Campbell found lysozyme to be a major allergen by ST, byt Langeland found that 0 of 68 sera from eggsensitive patients were positive for lysozyme using RAST.

      ovomucin:     Walsh et al. fond that ovomucin was a minor allergen in RAST studies using sera from egg-allergic subjects.

3. Structure - Epitopes

      Phosvitn - Walsh et al. also cincluded that phosvitin was a minor allergen in RAST analyses using sera from egg-allergic subjects.

      Some progress gjas been made in determining the T- and B- cell epitopes of ovalbumin, Shinoda et al. examined the T- cell proliferative response to ovalbumin in children with AD who were sensitive to egg protein. The proliferating cell population appears to be CD4+ CD45 RA+  T cells. The epitopes responsible for this proliferative response were not examined. However, a synthetic peptide prepared from ovalbumin demonstrates that sequences that are recognized by human IgE antibodies may also stimulate rabbit T cells. This peptide comprises amino acid sequences 323 to 339. Renz rt al. found this same sequence to be important in the generation of immediate hypersensitivity responses in Balb/c mice exposed via the respiratory route. T-cell clones for ovalbumin have been established. These cell lines appear to be CD4+ cell lines that secrete interleukin 4 (IL4), suggesting that these cells are of the T-helper 2 cell type (TH2).

      B-cell epitopes for ovalvumin have been more clearly established. Jhonsen and Elsayed semonstrated that IgE binding occurs with a peptide of amino acid sequence 323 to 339. Kahlert et al. using cyanogen bromide cleavage of a commercial ovalbumin preparation, demonstrated IgE binding to peptide sequences 41 to 172 and 301 to 385. Data obtained from studies of ovotransferrin (Gad d 3) show seven continuous epitopes. Ovomucoid has prominent carbohydrated domains. IgE binds to the glycosylated domains but not to the nonglycosylated domains, although it is questioned if the carbohydrate moity acts as an IgE-binding epitopes has been studie, and three discontinuous epitopes have been identified (Here are amino acid sequence!). It is of note that lysozme and bovine lactalbumin have approximately 43% sequence identity.

      Homology in the DNA sequence of egg white proteins and yolk apovitelin II has been repoted. It is possible that the yolk and white could have some IgE-epitope homology. Interstingl. Anet et al. found some cross-reactivity between eg yolk and egg white in RAST inhibition studies.

      Little is known about the dose of egg proteins required to elicit an immune response. Ovalbumin is not easily degraded. It is hypothesized to persist in the body and may stimulate memory B cells., possibly due to follicular dendritic cells retaining antigen-antibody complexes. although this theory has not been proven.