Human lymphotactin (Lptn)/XCL1, also named human SCM1 and ATAC, is a member of gamma or C subfamily of chemokines that lack two of the four invariant cysteine residues normally found in the CC and CXC chemokines and have an extended C-terminus. Human lymphotactin encodes a 114 amino acid precursor protein with a 21 amino acid predicted signal peptide. The gene for human and mouse lymphotactin has been mapped to chromosome 1. Human and mouse lymphotactin share approximately 60% amino acid sequence identity. The expression of lymphotactin is restricted to activated T cells such as activated CD8+ T cells and other class I MHC restricted T cells. Since lymphotactin is produced by lymphocytes and acts on lymphocytes, it is speculated that it is a messenger in T cell chemoattraction. Human lymphotactin is chemotactic for lymphocytes and NK cells. Its expression is abundant in some activated T cells such as activated CD8+ T cells and other class I MCH restricted T cells and is absent in CD4+ T cells. It has been shown that lymphotactin is a key regulator of lymphocyte motility and adhesion during acute allograft rejection. The specific receptor for lymphotactin is the orphan receptor XCR1 (GPR5). It has chemotactic activity for lymphocytes and natural killer cells but not for monocytes or neutrophils.

Secreted