A requirement for albumin as carrier for low molecular weight leukocyte chemotactic factors

Using a micropore filter assay, low molecular weight leukocyte chemotactic factors such as fatty acids, formyl-methionyl peptides, and peptides purified from dextran-activated plasma attract leukocytes suspended in albumin-containing media, but not cells suspended in media lacking in protein or containing non-albumin proteins. These factors become bound to albumin and can be eluted with it from Sephadex columns. The albumin-chemotactic factor complex attracts leukocytes more strongly than either the albumin or the chemotactic factor alone. It is suggested that albumin presents the chemotactic factors at the cell membrane in a form suitable to initiate a response which is not achieved by the same factors in free, low molecular weight form.