The Wiskott-Aldrich Syndrome protein (WASp) is a key regulator of actin polymerization in all hematopoietic cells and functions in leukocyte migration, adhesion and signaling. In humans, the Wiskott - Aldrich syndrome (WAS) is a severe X-linked immunodeficiency caused by loss of function mutations in WASp that lead to profound defects in immunity. In contrast, WAS patients exhibit increased IgE levels and atopic dermatitis/eczema. Our data in the mouse suggest that the elevated Type 2 response in the absence of WASp may be driven by innate immune cells rather than by classic CD4+ Th2 cells. Understanding specific effector defects in discrete leukocyte subsets will be critical for the appropriate treatment of pathology in WAS. We isolated the WASp deficiency to CD4+ T cells and examined the role of WASp in CD4+ T cell effector function in vitro and in vivo. Using this approach we have made key observations on Type 2 immunity that give us a novel handle on immunity in WAS and highlight differences in WAS-/- innate and adaptive compartments. We hypothesize that the heightened Type 2 response in human WAS (high IgE and atopic dermatitis) is compounded by robust innate IL-4 and enhanced recruitment/retention of Th2 cells to inflamed tissue. Specific Aim 1: Does loss of WASp in the innate compartment drive the Type 2 response? We have generated experimental systems that limit WASp deficiency to either innate or adaptive CD4 compartment. We will determine the kinetics, magnitude and effector function of Type 2 innate and CD4+ T cells at lymph node (LN) and dermal sites using an atopic dermatitis (AD) model in collaboration with Dr Raif Geha. Data from this aim will provide the first direct test of the principal contributing cell type(s) to Th2 pathology in WAS. Specific Aim 2: Does increased Th2 recruitment/retention in inflamed tissue compensate for reduced functional capacity? We find that WASp-deficient Th2 cells accumulate in the inflamed dermis more readily than WT Th2 cells suggesting WASp regulates tissue recruitment or retention. We will directly test recruitment of Th2 and non-T Type-2 cells with FACS and whole body imaging (Xenogen IVIS) in the AD model. For retention within the tissue we will use intravital 2-photon microscopy to assess interstitial motility and T-APC contact time and use adoptive transfer into the dermal site to follow tissue retention/exit.