The use of human CD68 transcriptional regulatory sequences to direct high-level expression of class A scavenger receptor in macrophages in vitro and in vivo

Macrophages (M phi) play a key role in innate and acquired immunity. The study of M phi biology has been hampered by the absence of suitable gene regulatory sequences for the overexpression of heterologous genes in M phi. The human CD68 gene encodes a glycoprotein that is expressed in monocytes and M phi, and therefore represents an attractive candidate gene for the generation of a M phi -specific gene-targeting vector. A transgene expression cassette that combines 2.9 kb of CD68 5' flanking sequence with the 83-bp first intron (IVS-1) of the CD68 gene, directed high-level, long-lasting expression of class A human scavenger receptor (hSR-A) isoforms in the murine M phi cell line, RAW-264. By using this CD68 expression cassette to generate M phi cell lines that overexpress a soluble secreted form of the extracellular portion of type T human SR-A, we were able to purify significant quantities of this protein and show its ability to inhibit SR-A-mediated endocytosis. Analysis of two independent lines of transgenic mice that expressed type III human SR-A under the control of the CD68 gene sequences revealed transgene mRNA expression in elicited M phi populations and in mouse tissues in a pattern that was consistent with M phi -specific gene targeting. These data show that CD68 transcriptional regulatory sequences can be used to direct high-level transgene expression in M phi in vitro and in vivo.