Influence of fetal calf serum on the results of the E rosette test

The sheep erythrocyte (E) rosette test was performed with and without fetal calf serum (FCS) in the medium, and using untreated and 2-amino-ethylthioisouronium bromide hydrobromide (AET)-treated E. Peripheral blood lymphocytes from 34 normal donors showed no significant difference in E rosette percentage between the tests performed with or without FCS. However, when using untreated E with FCS in the medium, patients with infectious mononucleosis and those with aseptic meningitis had a significantly decreased percentage of rosette-forming cells (RFC) as compared to the test performed without FCS. When AET-treated E were used, addition of FCS increased rosette formation of lymphocytes from patients with infectious mononucleosis, with stable multiple sclerosis and with brain tumours. Rosette formation with AET-treated E was generally increased when FCS was used, whereas decreased rosette formation was more common when FCS was used in combination with untreated E. The fact that significant differences in rosette formation associated with FCS have been found in certain patient groups, calls for caution when comparing results from laboratories that differ in the use or not of FCS.