CD154 expression on CD4+ T cells was assayed after stimulation (18 hours) with patient-specific WT or mutant RPC1 peptides, PAD4 peptide (negative control), or a pool of peptides from infectious agent antigens (CEFT, positive control). Healthy donors matched for one HLA-DR allele were used as controls. Experiments on SCL-4 (A) and SCL-42 (B) were repeated on separate blood draws, three and two times, respectively, with similar results. Gate frequencies are expressed as percentage of CD4+ T cells. (C) Frequency of peptide-reactive CD4 T cells expressed as fold change over CD154+ CD4 T cells in the unstimulated negative control.