Evaluation of purified natural killer cell functions in familial hemophagocytic lymphohistiocytosis

Abstract

Background: Familial hemophagocytic lymphohistiocytosis (FHL) is a rare, genetic, immune dysregulation disorder of aberrant hyperactivation of lymphocytes causing inflammation and hemophagocytosis. We report on a 3-month old male who was evaluated for the possibility of FHL because of a positive family history. The patient was asymptomatic; however, levels of the soluble interleukin 2 (IL-2) receptor were elevated and the quantity and function of the natural killer (NK) cells were severely decreased. Methods: Purification of NK cells and evaluation of the cytotoxicity and IFNγ/TNFα secretion of NK cells after IL-2 activation relative to the patient's family members. Results: The patient's NK specific lysis was enhanced compared with his mother, and it was slightly higher than his sister. The IFNγ and TNFα secretion by the patient's NK cells after challenge with target 721 cells or anti-natural cytotoxicity receptors (NKp30 and NKp44) antibodies showed levels that are close to the mother's and sister's NK secretion levels. Owing to a low yield of NK cells from the patient's father the results for his NK cells are incomplete. The patient did not undergo HSCT and continued to be followed. He is now 7 years old and thriving without signs of FHL. His last examination was in August 2012 for functionality of isolated NK cells. The results showed normal cytotoxicity, cytokine secretion, and CD107a up-regulation to the NK cell surface. Conclusion: We propose that NK function assessment in patients with presumed FHL should be performed on isolated NK cell populations. This practice may reduce the number of false-negative results in NK function assays. Statement of novelty: In this case report we show that functional assessment of unpurified NK cells could lead to a false-negative assessment in 1 of the parameters in FHL. Assessment of NK function without NK purification may lead to an erroneous diagnosis of poor NK function.