N. Matsumoto et al., H-2 allele specificity of the NK cell C-type lectin-like MHC class I receptor Ly49A visualized by soluble Ly49A tetramer, INT IMMUNOL, 13(5), 2001, pp. 615-623
Ly49A is a C-type lectin-like receptor on NK cells that recognizes MHC clas
s I ligands, H-2D(d) and D-k. The engagement of Ly49A with the ligands inhi
bits activation of NK cells and protects target cells from lysis by NK cell
s. Here we express the extracellular region of Ly49A with an N-terminal bio
tinylation tag in Escherichia coli to obtain soluble Ly49A (sLy49A) after r
efolding. sLy49A is indistinguishable from native Ly49A expressed on NK cel
ls serologically and in the ability to specifically bind H-2D(d) after tetr
amerization with R-phycoerythrin-coupled streptavidin. The fluorescently la
beled tetramer of sLy49A is applied to explore MHC class I haplotype specif
icity of Ly49A. We demonstrate the hierarchical reactivity of Ly49A with H-
2 of various alleles in the order of d > k, r > p > v > q > s > z. Reactivi
ty of sly49A tetramer to spleen lymphocytes from B10.QBR mice (H-2K(b), I-b
, D-q, Qa-1T/la(b)) but not from C57BL/10 mice (H-2(b)) identifies H-2D(q)
and L-q as candidates for a Ly49A ligand, Binding of sLy49A tetramer to H-2
D(q)- or L-q-transfected cell lines demonstrates that the two highly relate
d MHC class I molecules, H-2D(q) and L-q, are ligands for Ly49A. sly49A tet
ramer staining also demonstrates preferential expression of Ly49A ligand on
a subset of B cells in P/J mice. These results provide the basis to examin
e the molecular mechanism by which Ly49A discriminates polymorphic MHC clas
s I molecules.