CD4 and Alzheimer disease: In the 1990s the involvement of the immune system in AD has been suspected due to several experimental results; (a) the increase of CD8 suppressor/cytotoxic T cells (but less differentially CD4 helper cells) were found in the blood of AD patients (Singh, 1996; Singh and Cheng, 1996), (b) Serum S100 protein was elevated and exhibited in vitro binding of the 40 amino acid residues of β-amyloid peptides (Ab), and (c) the C1q complement component was elevated.