Deoxycytidyl-deoxyguanosine [(CpG)3] oligodeoxynucleotides (ODNs) signal through TLR9 to induce type-I IFN (IFN-alphabeta) and IFN-alphabeta-dependent MHC-I cross-presentation of exogenous antigens by dendritic cells (DCs). A puzzle was presented by our observation that three ODN classes, CpG-A, CpG-B, and CpG-C, had similar efficacy for induction of IFN-alphabeta-dependent MHC-I antigen cross-presentation by myeloid DCs despite greatly differing for induction of IFN-alphabeta (CpG-A>CpG-C>CpG-B). All ODN classes similarly enhanced plasmacytoid DC (pDC) presentation of exogenous MHC-I-restricted peptide, although pDCs did not cross-process protein antigen. MHC-I and the transporter for antigen presentation were induced by all ODN classes or IFN-alpha. CpG-B ODNs were slightly more potent than CpG-A or CpG-C ODNs for induction of low levels of IFN-alphabeta but less efficacious at high concentrations than CpG-A or CpG-C ODNs. Low levels of IFN-alphabeta induced by CpG-B ODNs sufficed for full induction of MHC-I cross-presentation. Thus, CpG-B ODNs are slightly more potent but less efficacious than CpG-A and CpG-C ODNs for induction of IFN-alphabeta. High sensitivity to IFN-alphabeta allows CpG-B ODNs to be equally efficacious for induction of MHC-I cross-presentation. CpG-B ODNs may be effective for inducing therapeutic responses that require low levels of IFN-alphabeta and may avoid unnecessarily high induction of IFN-alphabeta.