The role of the macrophage scavenger receptor in immune stimulation by bacterial DNA and synthetic oligonucleotides

To assess the role of the macrophage scavenger receptor type A (SRA) in imm une activation by CpG DNA, cytokine induction and DNA uptake were tested in vitro and in vivo using SRA knockout (SRA(-/-)) and wild type (WT) mice, A s a source of CpG DNA, Escherichia coli DNA (EC DNA) and a 20-mer phosphoro thioate oligodeoxynucleotide with two CpG motifs (CpG ODN) were used. In vi tro, both EC DNA and the CpG ODN induced dose-dependent increases of interl eukin (IL)-12 production by spleen cells and bone-marrow-derived macrophage s (BMM Phi) from both SRA(-/-) and WT mice. The levels of cytokines produce d by SRA(-/-) spleen cells and BMM Phi were similar to those of WT spleen c ells and BMM Phi. When injected intravenously with CpG ODN and EC DNA, both SRA(-/-) and WT mice showed elevated serum levels of IL-12. To investigate further the role of the SRA, flow cytometry and confocal microscopy were p erformed to examine the uptake of fluorescently labelled oligonucleotides. SRA(-/-) and WT BMM Phi showed similarity in the extent of uptake and distr ibution of oligonucleotides as assessed by these two techniques. Together, these findings indicate that, while the SRA may bind DNA, this receptor is not essential for the uptake of CpG DNA or its immunostimulatory activity.