When challenged in vitro with soluble β-amyloid peptides (Aβ1–42, Aβ 1–40, Aβ 25–35) only, the gross majority (on average, above 97%) of CFSE-loaded CD4+CD28+ lymphocytes of either healthy elderly or AD patients did not divide over 120 hours (Fig. 1). Here, CD28 is linked to Alzheimer disease.