Detection of microchimerism using nested PCR-SSP typing. (A) Pretransfusion DNA sample (recipient HLA type: A*0301, A*2402; B*4001, B*51011; Cw*0304, Cw*1502, all recipient bands arrowed; other bands are nonspecific). (B) Posttransfusion DNA sample (blood donor 1 HLA type: A*0101; B*0801, B*4402; Cw*0701, Cw*0704; blood donor 2 HLA type: A*2501, A*3002; B*3501, B*5501; Cw*0303, Cw*0401). Asterisked bands are those donor alleles detected; the pattern of recipient alleles and nonspecific bands is the same as that of a pretransfusion sample. Patient DNA was isolated from peripheral blood leukocytes and used in a primary amplification using HLA-A, -B, or -C primers.28 The resultant products were diluted 1:500 and used in a PCR-SSP typing system.19 The gel is run from negative (−) to positive (+).