CTSH and Alzheimer disease: Defects in the physical barrier in patients with AD result in an immune response,29 which typically includes an increase in mast cell numbers and macrophage and lymphocyte infiltration.30, 31 We saw no change in CD45+ cell (lymphocytes) numbers in the dermis or epidermis of either the Ctsh+/− or Ctsh−/− mice (Fig 6, A, and see Fig E6, B).