Differential expression of leukocyte receptor complex-encoded Ig-like receptors correlates with the transition from effector to memory CTL

human leukocyte receptor complex (LRC) on chromosome 19q13.4 encodes Ig sup erfamily receptors expressed on hemopoietic cells, Killer Ig-like receptors (KIR) are expressed in cytotoxic lymphocytes but other LRC molecules (Ig-l ike transcript(ILT)leukocyte Ig-like receptor (LIR)) are more ubiquitous. W e investigated expression of the ILT2/LIR1 inhibitory receptor compared wit h the related KIR, Both ILT2/LIR1 and KIR were expressed by peripheral CD8( +) T cells with a memory/effector phenotype. ILT2/LIR1(+) T cells demonstra ted diverse TCRBV repertoires in contrast to KIR+ T cells, while numbers of peripheral ILT2/LIR1(+) T cells were greater than KIR+ T cells and the maj ority of ILT2/LIR1(+) T cells did not coexpress KIR, Analysis of CD8(+) T c ells with specific HLA class I tetramers confirmed this pattern of expressi on, indicating differential regulation of LRC gene expression in T lymphocy tes, Only a minor proportion of TLT2/LIR1(+) KIR- clones survived in vitro cloning, were more susceptible to anti-CD3 or cognate peptide induced cell death than KIR+ T cells and exhibited lower levels of the Bcl-2 survival mo lecule. Our results indicate a sequential program of LRC-encoded receptor e xpression with initial ILT2/LIR1 expression in effector T cells and KIR gen e transcription in the minor proportion of expanded clones which survives a ctivation-induced cell death to become long term memory T cells.