Functional expression of soluble ICAM-1 by baculovirus-infected Sf9 cells

Inflammation, metastasis and ischemia are processes that require lymphocyte or leukocyte cell recognition and adherence to endothelial counter receptors such as ICAM-1. Mapping the sites of interaction of ICAM-1 with LFA-1, the receptor for ICAM-1 on lymphocytes, may lead to the design of novel inhibitors of inflammation or metastasis. To this end, recombinant soluble ICAM-1 cDNA was engineered into the baculovirus expression system, which is capable of expressing large amounts of proteins. These constructs were designed to contain a protein leader sequence so that the transfected insect cells would secrete the recombinant polypeptide into the culture media for ease of isolation. We engineered four constructs of ICAM-1 into the baculovirus system and obtained relatively high expression of two soluble forms of ICAM-1, a two domain and a five domain form. These truncated proteins were isolated and shown to promote adherence of HL-60 cells and Molt-4 cells. These recombinant soluble proteins also inhibited cell adherence to purified intact ICAM-1 isolated from K562 cells.