Decreased NK killing in patients with multiple sclerosis: An analysis on the level of the single effector cell in peripheral blood and cerebrospinal fluid in relation to the activity of the disease

Natural killer cell activity has earlier been shown to be depressed in patients with multiple sclerosis (MS) (Benczur et al., 1980). In the present study, this defect was more clearly characterized in different stages of the disease. By using a single-cell cytotoxicity assay in agarose (Grimm & Bonavida, 1979), in combination with the conventional 51Cr-release, the number of target-binding cells (TBCs) and the fraction of active killer cells therein could be compared with the radioisotope release in the different patient groups. It was found that patients with active and chronic MS showed lower natural killer (NK) activity in the 51Cr-release assay as compared with age and sex-matched controls, in contrast to stable MS patients who were comparable with their control group. The single cell cytotoxicity assay demonstrated that acute MS patients had a decreased number of TBCs in peripheral blood and that they also had a decreased percentage of active NK cells in their TBC fractions. Patients with chronic MS were normal in the single-cell cytotoxicity assay. When cells present in CSF were analysed in acute and chronic MS, few cells were found with target binding capacity and only in two instances out of 13 could any cytotoxicity at all be detected. Patients with other neurological diseases (OND) were found to have detectable NK activity in CSF in six cases out of ten in the single-cell assay. OND patients as a group also had higher peripheral NK activity in the 51Cr-release assay as compared with the control group. When peripheral and CSF cells from MS patients and OND patients were treated with interferon, no increase in TBCs or fraction of killer cells in TBCs was found. In the 51Cr-release assay, comparable increases in cytotoxicity were found in all groups. One possible explanation for the stage-related NK suppression seen in the present investigation may be a decreased interferon production combined with immune-complex induced, macrophage-produced prostaglandins which are known to influence the human NK system in a comparable way in vitro. Additionally, immune-complexes may directly interact with human NK cells as the majority of these are known to express receptors for the Fc portion of IgG.