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 (Mphi) play a key role in innate and acquired immunity. The study of Mphi biology has been hampered by the absence of suitable gene regulatory sequences for the overexpression of heterologous genes in Mphi. The human CD68 gene encodes a glycoprotein that is expressed in monocytes and Mphi, and therefore represents an attractive candidate gene for the generation of a Mphi-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 Mphi cell line, RAW-264. By using this CD68 expression cassette to generate Mphi cell lines that overexpress a soluble secreted form of the extracellular portion of type I 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 Mphi populations and in mouse tissues in a pattern that was consistent with Mphi-specific gene targeting. These data show that CD68 transcriptional regulatory sequences can be used to direct high-level transgene expression in Mphi in vitro and in vivo.