Activation of macrophages and B lymphocytes by an oligodeoxynucleotide derived from an acutely pathogenic simian immunodeficiency virus

Functional evaluation of HIV/SIV Nef as superantigen

It is speculated that a virus-encoded superantigen is involved in the pathogenesis of human and simian immunodeficiency virus infections and that the accessory protein Nef might be that superantigen. We are able to show, using a murine superantigen screening system, that Nef does not display features characteristic of a superantigen. Upon transfection into MHC class II expressing antigen-presenting cells, it is expressed, but fails to induce Vbeta-specific expansion of peripheral T lymphocytes, which is a characteristic feature of superantigens in mixed lymphocyte culture. Therefore, we cannot support the hypothesis that Nef is a superantigen. The observations in favor of that hypothesis must be explained by other mechanisms.

Phosphorothioate backbone modification modulates macrophage activation by CpG DNA

Macrophages respond to unmethylated CpG motifs present in nonmammalian DNA. Stabilized phosphorothioate-modified oligodeoxynucleotides (PS-ODN) containing CpG motifs form the basis of immunotherapeutic agents. In this study, we show that PS-ODN do not perfectly mimic native DNA in activation of macrophages. CpG-containing PS-ODN were active at 10- to 100-fold lower concentrations than corresponding phosphodiester ODN in maintenance of cell viability in the absence of CSF-1, in induction of NO production, and in activation of the IL-12 promoter. These enhancing effects are attributable to both increased stability and rate of uptake of the PS-ODN. By contrast, PS-ODN were almost inactive in down-modulation of the CSF-1R from primary macrophages and activation of the HIV-1 LTR. Delayed or poor activation of signaling components may contribute to this, as PS-ODN were slower and less effective at inducing phosphorylation of the extracellular signal-related kinases 1 and 2. In addition, at high concentrations, non-CpG PS-ODN specifically inhibited responses to CpG DNA, whereas nonstimulatory phosphodiester ODN had no such effect. Although nonstimulatory PS-ODN caused some inhibition of ODN uptake, this did not adequately explain the levels of inhibition of activity. The results demonstrate that the phosphorothioate backbone has both enhancing and inhibitory effects on macrophage responses to CpG DNA.

Beyond danger: unmethylated CpG dinucleotides and the immunopathogenesis of disease

Oligonucleotide sequences containing unmethylated cytidine phosphate guanosine (CpG) motifs are known to have significant immunostimulatory properties. Because of these immunostimulatory effects, unmethylated CpG oligonucleotides are thought to act as 'danger signals' that produce a favorable immune response by alerting the host to the presence of invading organisms or abnormal cells. In contrast to this concept, we review the evidence that unmethylated CpG sequences derived either from microbial agents or from endogenous CpG-rich Alu motifs promote disease progression by inducing an aberrant or autoreactive immune response. Recognition of the negative effect of unmethylated CpG dinucleotides should lead to more effective immune strategies to combat infectious, inflammatory, autoimmune and malignant diseases.