Human PRF1 peptide

Perforin-mediated lymphocyte cytotoxicity is critical for pathogen elimination and immune homeostasis. Perforin disruption of target cell membranes is hypothesized to require binding of a calcium-dependent, lipid-inserting, C2 domain. In a family affected by hemophagocytic lymphohistiocytosis, a severe inflammatory disorder caused by perforin deficiency, we identified 2 amino acid substitutions in the perforin C2 domain: T435M, a previously identified mutant with disputed pathogenicity, and Y438C, a novel substitution. Using biophysical modeling, we predicted that the T435M substitution, but not Y438C, would interfere with calcium binding and thus cytotoxic function. The capacity for cytotoxic function was tested after expression of the variant perforins in rat basophilic leukemia cells and murine cytotoxic T lymphocytes. As predicted, cells transduced with perforin-T435M lacked cytotoxicity, but those expressing perforin-Y438C displayed intact cytotoxic function. Using novel antibody-capture and liposome-binding assays, we found that both mutant perforins were secreted; however, only nonmutated and Y438C-substituted perforins were capable of calcium-dependent lipid binding. In addition, we found that perforin-Y438C was capable of mediating cytotoxicity without apparent proteolytic maturation. This study clearly demonstrates the pathogenicity of the T435M mutation and illustrates, for the first time, the critical role of the human perforin C2 domain for calcium-dependent, cytotoxic function. (Blood. 2009;113:338-346)

Adult hemophagocytic lymphohistiocytosis (HLH) is a rare and deadly hyperinflammatory syndrome presenting both diagnostic and therapeutic challenges. HLH may be primary, due to an underlying genetic abnormality, and/or secondary to infection, malignancy, or rheumatologic conditions. We describe a case of HLH-associated severe pulmonary hypertension paralleling Epstein-Barr virus (EBV) reactivation in a 52-year-old male in whom a novel perforin missense mutation was found (PRF1 1517C > T). Although intolerant of standard therapy (HLH-2004 protocol), a 6-week course of anti-CD52 (alemtuzumab) was associated with freedom-from-transfusion from weeks 4 to 13. However, 15 weeks after the onset of salvage therapy, he succumbed to polymicrobial sepsis despite treatment with prophylactic anti-infectives, with necropsy revealing disseminated blastomycosis and relapsed HLH. This case illustrates uncertainties in the relationships between pulmonary hypertension, a newly described PRF1 mutation, and possible pre-existing latent infectious risk factors (such as EBV or Blastomyces) in the pathogenesis and therapeutic perils of adult HLH.