The active E rosette test: correlation with delayed cutaneous hypersensitivity.

An active subpopulation of peripheral blood T lymphocytes, characterized by rapid (5-min) rosette formation with sheep erythrocytes (A-RFC), was measured in normal individuals after they were skin tested with microbial antigens. A significant rise in A-RFC occurred in all individuals who developed positive delayed cutaneous hypersensitivity (DCH) reactions, whereas skin test nonresponders showed no significant rise in A-RFC. No similar consistent changes occurred in populations of total T cells, characterized by longer (60-min) rosette formation with sheep erythrocytes, or in B cells, measured by immunofluorescence of surface immunoglobulin. The A-RFC response paralleled the DCH response in timing, but not in intensity. These results provide in vivo evidence for a biologically distinct T cell subpopulation, and focus attention on the A-RFC as immunologically active cells.