Comparative ability of Qdm/Qa-1^b, K^b, and D^b to protect class I(low) cells from NK-mediated lysis in vivo

The class Ib molecule Qa-1^b binds the class Ia leader peptide, Qdm, which reacts with CD94/NKG2R on NK cells. We have generated a gene that encodes the Qdm peptide covalently attached to β₂-microglobulin (β₂M) by a flexible linker (Qa-1 determinant modifier (Qdm)-β₂M). When this construct is expressed in TAP-2^- or β₂M^- cells, it allows for the expression of a Qdm-β₂M protein that associates with Qa-1^b to generate the Qdm epitope, as detected by Qdm/Qa1^b-specific CTL. To test the biological significance of expression of this engineered molecule, we injected TAP-2^- RMAS-Qdm-β₂M cells into C57BL/6 mice and measured their NK cell-mediated clearance from the lungs at 2 h. RMAS Cells transfected with Qdm-β₂M were resistant to lung clearance, similar to RMA Cells or RMAS cells in anti-asialo-GM₁-treated mice, while untransfected or β₂M-transfected RMAS cells were rapidly cleared. Further, pulsing RMAS cells with either Qdm, a K^b-, or D^b-binding peptide showed equivalent protection from clearance, indicating that a single class Ia or Ib molecule can afford complete protection from NK cells in this system. In contrast, injection of RMAS cells into DBA/2 animals, which express low levels of receptors for Qdm/Qa-1^b, resulted in protection from lung clearance if pulsed with a K^b or D^b-binding peptide, but not the Qa-1^b-binding peptide, Qdm.