Variants of SIRPα and mismatch detection in the current study. (A) Sequence alignment of the SIRPα immunoglobulin V domain variants. The sequences are from Takenaka et al.¹³ SIRPα v1 and v2 are the most common human variants. The residuals involved in CD47 interaction are under the red dots. The blue dots represent the specific hydrogen bond formed between CD47 and SIRPα v1.³⁷ The differences in interaction interfaces of SIRPα and CD47 on the DE and FG loops are highlighted in yellow.³⁷ Primer recognition sites are shown as blue arrows. Primer set 21376 + 21377 detects the presence of VI-type alleles, including v1, v4, v5, v6, and v9, and primer set 21376 + 21379 detects the presence of VII-type alleles, including v2, v3, v7, v8, and v10. (B) Sequence-Specific Primer (SSP) analysis of patient samples and controls. (C) SIRPα variants and mismatches detected in the current study. The mismatches were subclassified as G when more SIRPα VII allele is detected in the graft, or as H if more SIRPα VII variant is detected in the host.