PROCR and cytomegalovirus infection: Mutation of LES CDR3γ or CDR3δ, which minimally affected BTNL3 binding, eliminated LES binding to EPCR (Figure 3F; Figures S3H and S3I), consistent with the pronounced and highly focused expansion of the LES clonotype observed following cytomegalovirus (CMV) infection (Lafarge et al., 2005).