Disparate responses of lymphocyte clones to cells of monozygotic twins discordant for multiple sclerosis.

Spinal fluid and peripheral blood lymphocytes from patients with multiple sclerosis (MS) and other neurologic diseases (OND) were stimulated with a pool of allogeneic MS lymphocytes. Responding cells were cloned and assayed for their proliferative responses to peripheral blood lymphocytes from monozygotic twins discordant for MS. As expected, most (greater than 90%) responding clones proliferated equally well to cells from both members of a twin set. However, some clones were noted that responded to cells from one but not the other of the twin set. These differences could not be explained on the basis of a decreased stimulatory capacity of the twin cells. We cannot definitively explain our observations but they may suggest that environmental factors, perhaps exposure to a virus, could have altered the antigenic phenotypes of cells from identical twins discordant for MS. Further evaluation of the nature of these differences may lead to an understanding of the pathogenesis of the disease.