From the inception of FARRP (and even prior to that), one of the major research efforts has surrounded the identification of the proteins in foods that cause sensitization in susceptible individuals and the elicitation of allergic reactions in those individuals who are sensitized. Over the years, research has focused on allergens in commonly allergenic foods such as peanuts, soybeans, almonds, hazelnuts, Brazil nuts, and fish and in less commonly allergenic foods such as lupine, sunflower seeds, sesame seeds, and kiwi. During the first 10 years of FARRP, this area of research was led by our founding co-Director, the late Prof. Sue Hefle and included research done in collaborations with leading European research investigators including Stef Koppelman (now adjunct professor with FARRP) and Ronald van Ree. Recently, this area of research has been restimulated by the addition of Prof. Joe Baumert, the continuing collaborative efforts of Prof. Stef Koppelman and the activities of Prof. Rick Goodman relating to cross-reacting allergens. FARRP has also historically been interested in the stability of allergens to food processing unit operations and to digestion (proteolytic stability).
FARRP under the leadership of Prof. Baumert has recently entered into a collaborative research agreement with USDA-ARS and specifically with Dr. Soheila Maleki from the USDA Southern Regional Research Center in New Orleans. The USDA-ARS project is focused primarily on peanut and tree nut allergens including the identification and characterization of peanut, other legume, and tree nut allergens. However, the primary FARRP roles in this project will be focused on immunoassay development, evaluation and improvement and on peanut and tree nut thresholds.
A Ph.D. student in Prof. Goodman's laboratory (Afua Ofori-Anti) has recently investigated the role of the peanut agglutinin protein as a possible allergen. Previous research in other laboratories had suggested that peanut agglutinin was a minor peanut allergen based on its ability to bind IgE from the sera of some peanut-allergic individuals. However, these same individuals often had IgE binding to other peanut proteins as well. Dr. Ofori-Anti demonstrated that the IgE binding to peanut agglutinin was based largely upon carbohydrate epitopes (glycoprotein). This binding does not appear to be clinically significant and peanut agglutinin does not appear to be a peanut allergen.
Research led by Prof. Baumert in collaboration with Prof. Koppelman focused on the in vivo distribution of a digestion-resistant peptide of the major peanut allergen, Ara h 2. Ara h 2 is comparatively resistant to digestion and a digestion-resistant peptide (DRP-Ara h 2) is released in model digestion experiments. DRP-Ara h 2 could theoretically sensitize infants upon exposure through breast milk or could elicit reactions by skin contact from saliva. A competitive inhibition ELISA for DRP-Ara h 2 was successfully developed utilizing rabbit polyclonal antisera and applied to the analysis of serum, saliva and breast milk. The optimized ELISA has a limit of quantitation (LOQ) of 100 ng DRP-Ara h 2/ml in all body fluids. A study has been completed on the llevels of intact peanut protein and/or DRP-Ara h 2 in serum, saliva, and breast milk of humans after ingestion of peanut (publication pending). Robert Bush, M.D. (University of Wisconsin - Madison) and Michael Levy, M.D. (University of Wisconsin - Milwaukee) collaborated on the clinical aspects of the serum and saliva studies while David Hill, M.D. (Melbourne, Australia) designed and conducted the breast milk study providing samples to FARRP for analysis. DRP-Ara h 2 was detected in serum, saliva and breast milk during these investigations. The work on the purification and in vitro and in vivo digestion of the major peanut allergen, Ara h 2 (2S albumin), has provided insight into the stability of this allergenic 2S albumin and peptide fragments of this protein. Resistance to gastrointestinal digestion is believed to be a key characteristic of many food allergens due to the preservation of the protein structure. Sufficiently intact protein or immunologically active peptides derived from allergenic food proteins may be absorbed by gut epithelial cells or M cells and interact with the mucosal immune system for extended periods of time which may result in allergic sensitization. Prof. Baumert intends to continue conducting research on allergenic proteins and their digestive resistance.
A FARRP Ph.D. student, Ben Remington, under the joint supervision of Profs. Taylor and Baumert, has initiated research on soybean allergens. The clinical picture on the reactivity of soy-allergic individuals with various soy proteins is far from clear. Different individuals seem to react to different soy allergens although differences also appear to be influenced by the selection of methods and perhaps even by the selection of soy-based materials to use in the research. Thus far, research by other groups has determined that Gly m 5 and Gly m 6 (conglycinin and glycinin, respectively) are major soybean allergens. Gly m 3 (profilin) and Gly m 4 (a Bet v 1 homologue) are other important soy allergens. An oleosin from soy, called P34, is another potential soy allergen. The soy trypsin inhibitor (STI) has been identified as a minor allergen. FARRP is particularly interested in the levels of these allergenic proteins in various soy-based ingredients.
The Goodman group including Ph.D. student, Afua Ofori-Anti, and former post-doc, Dr. Pramod Siddanakoppalu, have evaluated IgE-binding cross-reactivity in among a wide taxonomic range of legumes. Methods have been developed to distinguish binding to carbohydrate determinants from binding to the peptide structure of proteins. Basophil histamine release has been used to evaluate the biological activity of the various legume proteins. Publications are pending.
A FARRP graduate student, Poi-Wah Lee (Ph.D. candidate) under the supervision of Prof. Taylor with collaboration from Prof. Koppelman is pursuing research on parvalbumin, the major allergen from fish. Parvalbumin has the distinction of being one of the first major food allergens to be identified and characterized. Considerable research has been done on parvalbumin from various species of fish over the years but much remains to be done. The major goals of Poi-Wah Lee's Ph.D. project will be:
- To investigate the effects of species, calcium, thermal processing, and Maillard reactions on the IgE and IgG binding characteristics of fish parvalbumins in the immunoassay
- To quantify the relative content of parvalbumin in various species of fish
- To determine the immunoreactivity of IgG and IgE to parvalbumin isotypes expressed in different species of fish
- To study the evolutionary relationship of parvalbumins and verify the IgE-binding epitopes of fish parvalbumins
Corn is not a major allergenic food and is, in fact, rarely allergenic. However, some corn-allergic individuals do exist. Because of the rare nature of this allergy, the allergens in corn have been incompletely studied. FARRP M.S. student, Harsha Ariyarathna under the supervision of Prof. Goodman conducted research to isolate the major food allergen, lipid transfer protein (LTP) from corn seed and evaluate differences in LTP content in seeds from 9 commercial hybrids of corn grown in two locations in Nebraska. This research also demonstrated that almost all of the LTP is concentrated in the embryo and pericarp of the seed.
The prevalence of tree nut allergy appears to be increasing in children in the United States. Walnut allergy is the most frequently reported among the tree nuts in the U.S. while pecan allergy currently ranks fourth. Both walnut and pecan belong to the Juglandaceae family, however, little information is currently available regarding the potential for clinical cross-reactivity between these closely related tree nuts. FARRP M.S. student, Jelena Spiric under the supervision of Prof. Baumert, is conducting research on characterization and stability of pecan allergens, and is examining the potential clinical cross-reactivity of pecan and walnut allergens using sera from pecan and walnut allergic individuals.
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