Influence of food processing on the humoral and cellular immune response to shared and unique allergens of crustacean species

Shellfish allergy is a significant health issue, particularly amongst the adult population. Importantly, shellfish are a common cause of food-induced severe allergic reactions, including anaphylaxis. However, as is the case with most food allergies, the diagnosis, treatment and management of the condition can be quite difficult especially when the sensitising or offending foods are not specifically known by the patient. A limited understanding of clinical cross-reactivity between shellfish species, and how food processing, such as heating and digestion, can affect shellfish allergens in terms of their allergenicity also impedes the diagnosis and management of this allergy . There is currently no cure or effective long term treatment (apart from food avoidance) for shellfish allergy. However, the identification and characterisation of shellfish allergens, and the effect food processing has on these, provides insight into sensitisation and allergic processes. The results presented within this thesis have shown that raw and cooked crab and prawn extracts are able to bind IgE, with cooked extracts showing stronger IgE binding. IgE reactivity was found to be clinically relevant by assessing the activation of basophils by extracts in vitro. Frequency of IgE reactivity differed between raw and cooked extracts, with different allergens contributing to IgE reactivity depending on whether the extract had been processed or not or whether it was from crab or prawn. Allergens identified within this study from raw and cooked mud crab were tropomyosin, arginine kinase, haemocyanin, enolase and myosin light chain. Raw and cooked extracts were all highly IgE cross-reactive, with the major allergen tropomyosin being an important factor in this cross-reactivity. Evidence of cross-reactive, crab-specific IgE was also found which does not cross-react with prawn species. Tropomyosin was found to be resistant to digestion by gastric enzyme pepsin (retained IgE-reactivity), while other shellfish allergens were susceptible to pepsin but resistant to intestinal enzyme trypsin digestion. Both raw and cooked extracts were able to induce proliferation of a number of different cell types in the peripheral blood mononuclear cell population of shellfish-allergic individuals, particularly the CD4+ cell population. These cells were associated with a higher proportion of intracellular IL-4 (major cytokine in driving Th2 [allergic] immune responses) than CD4+ cells from non-atopic controls. This study has created a strong foundation for ongoing research, addressing how food processing of shellfish allergens affects the allergic immune response. Such information is vital for improving diagnosis and management of shellfish-allergic subjects, as well as informing the development of potential therapeutic options in the future.