Yeast cells containing plasmids for displaying antigenic peptides were grown at 30uC for 24 h in SDCAA medium and induced at 20uC for 36 h in SGCAA medium. 1610 7 cells were harvested by centrifugation, incubated with goat antisera (1:100 diluted in 100 mL of PBS) and labeled with 1 mg of FITC conjugated antigoat IgG secondary antibody as described above. Labeled cells were resuspended to 5610 7 cells/mL, fixed with 4% paraformaldehyde and photographed on a Zeiss 710 laser scanning confocal microscopy (Carl Zeiss, Germany) at the Center of Biomedical Analysis, Tsinghua University. Yeast cells containing nonexpressing vector pCTCON-2 and HA1-expressing vector pCTCON-HA1 were treated in the same way as negative and positive controls, respectively.