CD8⁺ T cells from LGLL patients display enhanced lysis of a normal pulmonary artery endothelial cell line. (A) Percentage of CD56⁺, CD8⁺, and CD4⁺ T cells by flow cytometric analysis in unsorted and sorted populations after negative selection using RosetteSep. (B) CD8⁺ T cells were purified from LGLL patients and healthy blood donors. Direct cytotoxicity was performed using 5-hour ⁵¹Cr release assays. CD8⁺ T cells were incubated with ⁵¹Cr-labeled CRL-2598 endothelial cells at an E/T ratio of 50:1, and the CD8⁺ T-cell–mediated cytolysis of CRL-2598 cells was compared among LGLL patients (n = 9) and healthy controls (n = 9). (C) CD8⁺ T cells from LGLL patients are cytotoxic toward synovial cells. CD8⁺ T cells were purified from LGLL patients and healthy blood donors. Direct cytotoxicity assays were performed using 5-hour ⁵¹Cr release assays. CD8⁺ T cells were incubated with ⁵¹Cr-labeled HTB293 synovial cells at an E/T ratio of 50:1. CD8⁺ T-cell–mediated cytolysis of HTB293 cells was compared among 9 LGLL patients and 9 healthy controls. (D) CD8⁺ T cell–mediated cytolysis of CRL-2598 cells was compared among patients presenting with LGLL and PAH (n = 3), PAH without LGLL (n = 2), and healthy controls (n = 3). The mean and SEM of triplicate wells are shown.