Administration of human umbilical cord blood cells (HUCBC) or HUCBC-derived plasma is used to treat amyloid-based diseases, such as Alzheimer's disease, Huntington's disease, cerebral amyloid antigopathy, and type-II diabetes. Modulating inflammatory reactions by infusing HUCBC resulted in a marked reduction of amyloid plaques and immune-associated cellular damage. HUCBC infusion also significantly reduced cerebral amyloid angiopathy in mice models. These effects were associated with suppression of the CD40-CD40L interaction and a reduction in surface expressed CD-40 was observed on immune cells. Further, Aβ phagocytic activity was increased and soluble and insoluble Aβ protein levels were modulated by treatment. HUCBC-infused sera also significantly increased phagocytosis of Aβ1-42 peptide and inhibited immune cell CD40 expression and reduced cerebral amyloid angiopathy.