Detection of antigen specific rosette formation with the FACS

Donors previously sensitized to conventional antigens PPD and KLH were evaluated for their antigen binding responses, utilizing a rosette forming technique with antigen-conjugated autologous erythrocytes. Reactivity is directly correlated with prior sensitization. Furthermore, antigen specificity is suggested by inhibition of rosette formation by prior incubation with the relevant antigen. The frequency of RFCs detected cytofluorometrically was compared with conventional fluorescent microscopy determinations. RFCs detected in this manner were identified as antibody armed monocytes by cell depletion and histochemical studies. The usefulness of the rosette forming technique for the routine evaluation of donor immunity is discussed.