IDENTIFICATION OF A NOVEL HLA-B27 SUBTYPE BY RESTRICTION ANALYSIS OF A CYTOTOXIC GAMMA-DELTA T-CELL CLONE

Seven HLA-B27 alleles are known, which share the same allospecificity, but differ by one to six amino acid substitutions. Herein, we describ e a novel HLA-B27 allele, provisionally named B27-ci, which is express ed by an individual from whom a B27-restricted gamma delta T cell clon e has been derived. This clone recognizes B cell lines from the proban d and all of the other B27-positive members of the family, but does no t lyse B cell lines that express other HLA-B27 alleles. The am ino aci d sequence deduced from three B27-ci cDNA clones was found to differ f rom the B2705 sequence by one amino acid substitution (Asp to His) in position 116 of the alpha 2 domain. This position has been shown to l ie in the floor of the F pocket, where it plays a key role in determin ing the nature of the amino acid side chain that will fit into this po cket. Moreover, the fact that the clone described here possesses a TCR -gamma delta indicates that this subset of cells not only can be HLA-r estricted, but also can finely discriminate among classical class I mo lecules.