Characterization of a novel human scavenger receptor cysteine-rich molecule SCART1 expressed by lymphocytes

The scavenger receptor cysteine-rich (SRCR) superfamily is a group of membrane bound and secreted proteins expressed by cells of the immune system. Several members act as pattern recognition receptors that bind to conserved molecular structures of pathogens. We have previously characterized a member of the SRCR superfamily, mSCART1, which primarily is expressed on a large subset of γδ T cells in mice. Here we report the cloning and characterization of human SCART1 (hSCART1) mainly expressed by CD4+ and CD8+ T lymphocytes. The hSCART1 gene maps to chromosome 10, region q26.3, a region that displays synteny to the position of mSCART1 in the murine genome. The primary structure of hSCART1 was established by molecular cloning. The longest cDNA sequence of hSCART1 that was found is 2200 bp and encodes a protein composed of a signal peptide, 5 SRCR domains, and an in-frame potential cytoplasmic domain. Shorter splice forms have also been isolated. Quantitative real-time PCR analysis on human blood-fractions has shown that hSCART1 is expressed primarily by CD4+ and CD8+ T lymphocytes with either αβ or γδ T cell receptors, and real-time PCR on 22 different human tissues showed high expression of hSCART1 in the small intestine and colon. An antibody raised against an N-terminal hSCART1 peptide stains a subset of cells in the small intestine, stomach, and gall bladder, and it also stains placental villi. In conclusion, the characterization of hSCART1 at the mRNA and protein level suggests that the protein plays a role in the immune system, perhaps as a co-receptor on αβ and γδ T cells.