A study of some immunological variables in twins, discordant for multiple sclerosis

11 twin pairs, discordant for multiple sclerosis (MS), were studied: 5 were monozygotic, 6 dizygotic. The mixed leukocyte reaction (MLR) with cells from unrelated patients with MS, the natural killer cell (NK) activity, OKT 4/OKT 8 ratio, and monocyte numbers were studied. The impaired MLR seen in some patients with MS was even more pronounced in the healthy twin, irrespective of the zygosity of the twins. A reduced NK activity and a high OKT 4/OKT 8 ratio is seen in the diseased twin compared to the healthy one, more strongly indicated at monozygosity. The significance of genetics, early environment, and disease is discussed.