Natural killer cell number and activity in multiple sclerosis

Natural killer (NK) cell percentage among cells appearing in lymphocytic flowcytometric gate, and their concentration per unit volume of peripheral blood, as well as NK-cell in vitro activity, were determined in 45 patients with multiple sclerosis (MS, 34 with definite and 11 with probable diagnosis). Two age- and sex-matched control groups consisted of 27 healthy individuals and 19 individuals with other neurological diseases, respectively. NK cells were identified on the basis of their reaction with monoclonal antibody NKH-1, and NK-activity on the basis of their spontaneous killing of K-562 erythroleukemia target cells with mononuclear cells from peripheral blood. MS patients were analyzed in regard to the phase (active, stable inactive, stable progressive) and course (remittent, remittent-progressive, progressive) of the disease. In general, MS patients tended to have both lower number and activity of natural killer cells than either of the two control groups. A statistically significant decrease was found for the concentration of NKH-1 + cells in the blood of all MS patients, for the number of lymphocytes in the blood of patients with remittent course of the disease, and for the number of NKH-1 + cells in the blood of patients with progressive course of the disease. It appeared that more profound defects were associated with the progression of the disease; NK-cell number always appeared more affected than NK-cell activity. In MS patients, NK-cell activity correlated significantly with NK-cell percentages among lymphocytes but poorly with the concentration of NKH-1 + cells in the blood. In healthy controls, neither of the two correlations was significant. Taken together, our data suggest that more active NK-cells are more resistant to the adverse influence of factors that decrease NK-cell number in MS.