Lymphocytic activation in peripheral blood and cerebrospinal fluid during the course of chronic relapsing experimental allergic encephalomyelitis

A monoclonal antibody against the human interleukin-2 receptor (anti-Tac) has been found to cross-react with an antigen on the surface of guinea pig leucocytes. Cells marking with anti-Tac and with an anti-pan T cell monoclonal antibody have been quantitated in the peripheral blood and cerebrospinal fluid (CSF) of guinea pigs with chronic relapsing experimental allergic encephalomyelitis (CR-EAE). T cells account for about 90% of peripheral blood leucocytes in all animals whilst in the CSF, T cells are the major contributor only when there is a pleocytosis. The proportion of T cells marking with anti-Tac, a measure of T cell activation, in blood and CSF of control animals is 12%, rising to 23% in blood in the post-acute phase of the disease. However, a fall in the blood Tac/T ratio to 13% occurs during the first 10 days of relapse with a subsequent rise to 30–35%. This change is related to the time after onset of relapse irrespective of the subsequent course of the disease. From first relapse onwards CSF lymphocytes show a greater level of activation than lymphocytes from paired peripheral blood samples but the proportion of Tac + cells in CSF does not increase with increasing CSF pleocytosis. The data is consistent with migration of activated T cells from blood to CSF at the onset of relapse.