WAS and immunodeficiency disease: For instance, in the absence of WASP function, uptake of particulate antigen by macrophages by means of phagocytosis is defective,6-12 podosome formation and T-cell priming ability of dendritic cells (DCs) is impaired,6,13-15 B- and T-cell proliferation in response to B- or T-cell receptor ligation is reduced,16-20 and homeostasis of mature B-cell populations,21,22 as well as homeostasis and function of regulatory T cells, is disturbed.23-26 Therefore the severe immunodeficiency resulting from WASP deficiency is thought to be the result of a complex combination of cellular immune defects.