Development of protein microarrays for detection of autoantibodies. A. Detection of p53 antigen with standard ELISA, using reference p53-antibody positive sera and negative sera. B and C. 4 antigens (S100A7, p21, ML-IAP, and p53) are expressed in microarray format, and p53 antigen is specifically detected with the reference sera. All four proteins are strongly expressed, as measured by detection of GST tag using anti-GST antibody. D. Sensitivity of detection. P53 positive serum was serially diluted and tested by standard ELISA and NAPPA. Standard deviation for ELISA was based on two samples and for NAPPA was based on four features on the array.