New decision-tree model for defining the risk of reproductive failure.

PROBLEM: Natural killer (NK) cells play a key role in embryo implantation and pregnancy success, whereas blood and uterine NK expansions have been involved in the pathophysiology of reproductive failure (RF). Our main goal was to design in a large observational study a tree-model decision for interpretation of risk factors for RF. METHODS OF STUDY: A hierarchical multivariate decision model based on a classification and regression tree was developed. NK and NKT-like cell subsets were analyzed by flow cytometry. RESULTS: By multivariate analysis, blood NK cells expansion was an independent risk factor for RF (both recurrent miscarriages and implantation failures). We propose a new decision-tree model for the risk interpretation of women with RF based on a combination of main risk factors. CONCLUSIONS: Women with age above 35 years and >13% CD56⁺CD16⁺ NK cells showed the highest risk of further pregnancy loss (100%).

Functional assessment of perforin C2 domain mutations illustrates the critical role for calcium-dependent lipid binding in perforin cytotoxic function.

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.