Background: Primary immune deficiencies of natural killer (NK) cells have been described in patients with a susceptibility to herpes infections.
Aims: To assess the diagnostic utility of measurement of NK cytotoxicity in patients with recurrent oral herpes infections.
Methods: A retrospective audit was carried out on results obtained over an 18-month period, from 28 NK cell cytotoxicity assays (24 patients; all with a history of recurrent oral herpes infections), and 24 control samples (three healthy donors). Percentage specific cytotoxicity (PSC) was determined by measurement of the percentage of K562 target cells lysed by NK cells after incubation, using the NK TEST. Comparison of PSC was made with reference ranges provided.
Results: No patient with absent NK/NKT cells or NK cell cytotoxicity was identified (95% CI 0 to 14.8%). Two patients had persistently low PSC. Two patients with reduced PSC showed PSC within the normal reference range on repeat testing. Patient and control samples were seen both above and below the reference ranges. A relationship was expected between NK cell percentage and PSC; however this correlation was not significant (r(s)=0.29, p=0.18, 95% CI -0.14 to 0.63).
Conclusions: A deficiency of NK cell cytotoxicity has not been identified in this cohort. An apparent reduction in cytotoxicity may be due to normal interpersonal and intersample variability in NK cytotoxicity. Without reference ranges established from a large population of control samples to account for this, a reduction in PSC is difficult to define. Further studies are required to identify if a correlation exists between the percentage of NK cells and PSC.