Blood samples
At baseline and follow up visits, 10mL of venous blood will be collected by trained study staff. The blood will be processed for plasma, peripheral blood mononuclear cells, and granulocytes within 4 hours of receiving the sample. Plasma will be stored at -80C for batched analysis of specific IgE and specific IgG4 against whole peanut/tree nuts and corresponding components by ImmunoCAP (Phadia AB, Uppsala, Sweden). Peripheral blood mononuclear cells and granulocytes will be isolated using a Ficoll-paque density gradient and stored in liquid nitrogen for exploratory immunological studies. In addition, follow up visit blood samples will have Basophil Activation Tests (BATs) performed within 4 hours, with basophils isolated and tested for expression of activation markers CD63 and CCR3+ following specific peanut/tree nut allergen stimulation in vitro.