Reduced degranulation of NK cells in patients with frequently recurring herpes

Abstract

NK cells lyse virus-infected cells by degranulation; however, alterations in NK cell degranulation in persistent viral infections have not been directly studied. Earlier reports have documented a decrease in NK activity in patients with frequently recurring herpes (FRH). We corroborate these findings by showing that the degranulation responses of blood NK cells from patients with FRH, both during relapse and during remission, are significantly lower than those in healthy donors. The impaired degranulation was probably not caused by defective target cell recognition, since it was observed upon stimulation both with K562 cells and with a receptor-independent stimulus (phorbol 12-myristate 13-acetate plus ionomycin). We also show that the intracellular expression of perforin and CD107a by NK cells from patients with FRH is not different from that in healthy donors, thus excluding that the low NK cell degranulation in FRH is caused by a smaller size of the lytic granule compartment. We confirm previous reports on lowered NK activity in FRH patients and show that NK activity is significantly impaired only during remission, but not relapse; the causes for the discrepancy between the low degranulation and "normal" NK cell activity during relapse are discussed. In all, these data point at the deficit of NK cell degranulation in FRH. Whether this is a predisposing factor or a consequence of herpes simplex virus infection requires further investigation.

Fig. 1.

Typical pattern of the degranulation of NK cells from a healthy donor (upper row) and a patient with FRH in recurrence (middle row) and in remission (lower row) without stimulation and in response to K562 cells, phorbol 12-myristate 13-acetate plus ionomycin (PMA+ION), and phorbol 12-myristate 13-acetate plus ionomycin plus cytochalasin B (PMA+ION+CB). NK cell degranulation assay was performed as described in Materials and Methods, and the results were assessed by flow cytometry. Shown are the results for gated CD3⁻ CD56⁺ NK cells. The numerators indicate percentages of NK cells that have externalized CD107a during the 4-h incubation period, and the denominators indicate the mean fluorescence intensity (MFI) of CD107a on CD107a⁺ NK cells (in arbitrary units).

Fig. 2.

NK activity in healthy donors (n=51) and patients with FRH upon recurrence (n=28) and remission (n=23). MNCs from patients and donors were incubated for 4 h with K562 target cells at the indicated effector/target (E:T) ratios, and the percentages of killed K565 cells were determined as described in Materials and Methods. Squares, diamonds, and triangles denote medians of respective groups; bars represent the 10th and 90th percentiles. *, P < 0.05 (comparison between healthy donors and FRH patients in remission at this E:T ratio).