Antigen-stimulated rosette formation by T lymphocytes in experimental allergic encephalomyelitis.

Peripheral blood lymphocytes form rosettes in the presence of heterologous etythrocytes. Spontaneous or active rosette formation has been reported to be a measure of circulating and immunologically functional thymus-dependent lymphocytes. The present study utilizes the rosette assay to measure changes in the circulating T cells of guinea pigs sensitized with encephalitogenic myelin basic protein (BP) or with nonencephalitogenic peptide S42 known to induce cellular transformation in experimental allergic encephalomyelitis, a cell-mediated disorder of the central nervous system. The results show a significant depression in the number of active but not in the total number of rosette-forming T lymphocytes from the peripheral blood of antigen-sensitized animals. This reduction, which was not related to the encephalitogenic property of the BP, was readiiy reversible by incubating lymphocytes with the sensitizing antigen but not with histone. Under these conditions, lymphocytes from unsensitized control animals were unresponsive to stimulation by any of the antigens used. The antigenstimulated rosette assay described in this report provides a specific assay for sensitization to basic protein in BP-related demyelinating diseases.