Prior to yeast library screening, nonspecific interactions of serum samples (i.e., mouse, goat or human antisera) with yeast proteins were removed by incubation with induced yeast cells carrying the control vector pCTCON-2. To label cells for FACS, 1610 7 (For yeast EBY1001 cells, OD 600 <1610 7 cells/mL) freshly induced library cells were pelleted at 8,000 g for 1 min in a 1.5 mL microcentrifuge tube and washed two times with 1 mL of 16Phosphate Buffered Saline (PBS). Cells were then incubated with 100 mL of pre-absorbed serum (1:50 diluted in PBS) at 4uC for 1 h. Unbound antibodies were removed by washing two times with 1 mL of PBS. The library cells were incubated with 1-2 mg of fluorescein isothiocyanate (FITC) or phycoerythrin (PE) labeled secondary antibodies in 100 mL at 4uC for 45 min. After washing two times with PBS, cells were resuspended in 1 mL of PBS and loaded onto a BD-FACS AriaII TM machine (Shanghai, China) for sorting. Yeast cells harboring the pCTCON-2 vector were processed as described above and used as a negative control. The positive gate was set to exclude all negative control cells (,0.1% leakage). The total amount of cells used for sorting was adjusted to ensure that more than 1610 5 cells could be harvested, which were then collected in 5 mL of SDCAA medium and grown overnight at 30uC with shaking.