Reduction of IgG levels in human adult serum results in increased expression of CD1a, CD1b, and CD1c, and decreased expression of CD1d on dendritic cells. The expression of CD1 molecules was determined on monocyte-derived DCs after 6 days of culture in IL-4 and GM-CSF and FCS, AS, or AS with reduced IgG content. To reduce the levels of IgG in AS, the serum was diluted 10 times in RPMI and passed through a protein G column twice to allow binding of IgG. As a control, immunoglobulins were added back to the AS after protein G binding. After 6 days of culture, the cell surface expression of CD1a (A), CD1b (B), CD1c (C), and CD1d (D) on DCs was determined by flow cytometry. The graphs show the MFI of CD1 expression from 1 representative donor of 4.