Specificity of preformed alloantibodies causing B cell positive flow crossmatch in renal transplantation

The specificity of alloantibodies (alloAb) and their clinical significance in association with T - /B + flow cytometry crossmatch (FCXM) in kidney tra nsplantation are not clearly defined. This study was undertaken to examine the HLA specificity and clinical relevance of Ab causing B + FCXM in pre-tr ansplant (final XM) recipients' serum samples. Final FCXM serum samples wer e analyzed from 457 renal transplant patients followed for 10 months post-t ransplantation. Two hundred and sixty patients had T - /B + final FCXM. The control group included 197 recipients with T - /B - FCXM at time of transp lantation. Class I/class II PRA and specificity of anti-HLA class I and cla ss II Ab in final FCXM serum samples were analyzed by FlowPRA Class I Scree ning Test and FlowPRA Class II Screening Test. We found no correlation betw een graft outcome and pre-transplant T - /B - and T - /B + FCXM status. Add itionally, we observed no clinical relevance of B + FCXM in retransplant pa tients. However, MCS greater than or equal to 200 in B + FCXM retransplant recipients was associated with anti-class II Ab to previous mismatches in r egrafted patients (n = 46). This finding was confirmed by specificity analy sis of anti-DR/DQ Ab in patients with high (greater than or equal to 15%) c lass II PRA. In 63% (12 of 19) of retransplants having T - /B + FCXM, we de fined the specificity of alloAb to first graft mismatched class II antigens . In contrast, anti-class II Ab was detected in only 5.7%, (2 of 35) of sin gle-graft recipients with different PRA values. Significantly greater MCS ( 240 +/- 61 vs. 163 +/- 48; p = 0.022) was observed in retransplant patients having short (less than or equal to 5 m) previous graft survival time (PGS T) than in those with long PGST (greater than or equal to 5 m). Only 2% of retransplant recipients with B + FCXM had non-HLA Ab. In contrast, the over whelming majority of primary recipients had no detectable alloAbs. No signi ficant difference in class I PRA was found between B - and B + FCXM recipie nts. However, class II PRA was significantly higher in patients having B FCXM (p = 0.028), Collectively, these data show that MCS intensity is not a lways a reliable criterion for anti-HLA Ab detection because of the presenc e of non-HLA Ab. These results can be explained by low titers of anti-class II Ab, at which concentration these Ab cannot produce a deleterious effect . FlowPRA and Flow screen beads appeared to be reliable and sensitive metho ds for detection and specificity analysis of anti-class II alloAb.