Simonetta Verdiani

Molecular clones of the p58 NK cell receptor reveal immunoglobulin-related molecules with diversity in both the extra- and intracellular domains

Recognition of major histocompatibility class I molecules on target cells by natural killer (NK) cells confers selective protection from NK-mediated lysis. Cross-linking of the p58 NK receptor, involved in the recognition of HLA-C alleles, delivers a negative signal that prevents target cell lysis. Molecular cloning of the p58 NK receptor reported here revealed a new member of the immunoglobulin superfamily. Five distinct p58 receptors, with sequence diversity in the immunoglobulin-related domains, were identified in a single individual. All NK clones tested expressed at least one p58 member. Three different types of transmembrane and cytoplasmic domains exist, even among receptors with closely related extracellular domains. These data revealed a repertoire of NK cells with clonally distributed p58 receptors exhibiting diversity in both extracellular and intracellular domains.

p49, a putative HLA class I-specific inhibitory NK receptor belonging to the immunoglobulin superfamily

NK cells display several killer inhibitory receptors (KIR) specific for different alleles of MHC class I molecules. A family of KIR are represented by type I transmembrane proteins belonging to the immunoglobulin superfamily (Ig‐SF). Besides cDNA encoding for these KIR, additional cDNA have been identified which encode for Ig‐SF receptors with still undefined specificity. Here we analyze one of these cDNA, termed cl.15.212, which encodes a type I transmembrane protein characterized by two extracellular Ig‐like domains and a 115‐amino acid cytoplasmic tail containing a single immuno‐receptor tyrosine‐based inhibitory motif (ITIM) which is typical of KIR. cl.15.212 cDNA displays approximately 50 % sequence homology with other Ig‐SF members. Different from the other KIR, cl.15.212 mRNA is expressed by all NK cells and by a fraction of KIR+ T cell clones. cl.15.212 cDNA codes for a membrane‐bound receptor displaying an apparent molecular mass of 49 kDa, thus termed p49. To determine the specificity of the cl.15.212‐encoded receptor, we generated soluble fusion proteins consisting of the ectodomain of p49 and the Fc portion of human IgG1. Soluble molecules bound efficiently to 221 cells transfected with HLA‐G1, ‐A3, ‐B46 alleles and weakly to ‐B7 allele. On the other hand, they did not bind to 221 cells either untransfected or transfected with HLA‐A2, ‐B51, ‐Cw3 or ‐Cw4. The binding specificity of soluble p49‐Fc was confirmed by competition experiments using an anti‐HLA class I‐specific monoclonal antibody. Finally, different cDNA encoding for molecules homologous to cl.15.212 cDNA have been isolated, two of which lack the sequence encoding the transmembrane portion, thus suggesting they may encode soluble molecules.

p49, a putative HLA classs I-specific inhibitory NK receptor belonging to the immunoglobulin super-family (Vol 28(6) 1998, pp 1980-1990)

Page 1980 Due to a printing error the affiliation given for Michele Cilli was wrongly indicated; the correct affiliation is: Istituto Scientifico Tumori and Centro Biotecnologie Avanzate, Genova, Italy