Injection of lymphotactin (Lptn) into the peritoneum caused an influx of lymphocytes at 24 h. Phenotypic analysis of the cellular influx showed that a large proportion of these cells were T lymphocytes; however, a large number of NK cells was also present. This effect of murine Lptn (mLptn) was specific since the cellular influx was blocked with a mLptn-specific mAb. Similar results were observed when Lptn was injected s.c. and the tissue was analyzed by immunohistochemistry using an anti-CD3epsilon mAb. Microchemotaxis assays confirmed that murine NK cells respond to mLptn, and also showed human NK clones to be similarly responsive to recombinant human Lptn (rhLptn). Immunohistochemical analysis of IL-2-activated murine NK cells and Northern analysis of human NK clones revealed that these cells also produce Lptn, suggesting that a self-regulatory migration mechanism exists in NK cells. Together these data confirm, in vivo, the lymphocyte specificity of Lptn previously observed in vitro and extend its chemotactic effects to the NK cell lineage. We also investigated the functional consequences of truncating the carboxyl terminus of hLptn. This truncated molecule (which is missing the carboxyl-terminal 22 amino acids of hLptn) had no detectable activity on human PBLs. In addition, while hLptn was found to attract murine splenocytes in vitro, the carboxyl-terminal truncated hLptn was again inactive on murine splenocytes. This observation indicates the presence of structural features in the carboxyl terminus of Lptn that are necessary for its biologic activity.

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