Flow cytometric evaluation of pregnancy-induced anti-HLA immunization and blood transfusion-induced reactivation.

Background: Pregnancy-induced alloimmunization (PIA) may decrease to a level that becomes undetectable by complement-dependent cytotoxicity (CDC). Nevertheless, such alloimmunization may provoke acute rejections after kidney transplantation and lead to broad-spectrum immunizations after transfusion. Flow-cytometry (FC) was used to estimate the frequency of low-level PIA and to evaluate its influence on posttransfusion alloimmunization profiles.

Methods: To evaluate the frequency of low-level PIA, the sera of 36 women, free of CDC-detectable anti-HLA IgG (CDC-IgG- negative), were cross-matched by FC against their husband's or offspring's lymphocytes and further analyzed with human leukocyte antigen (HLA) Ag-coated microbeads (Flow-PRA One-Lambda, Canoga Park, CA). To evaluate the influence of low-level alloimmunization on posttransfusion appearance of CDC-IgG, pretransfusion sera of a second cohort of 43 women, also CDC-IgG-negative and included in a transfusion protocol, were analyzed by Flow-PRA. Posttransfusion sera were analyzed for the development of cytotoxic IgG.

Results: Ten of the first cohort of 36 (27.8%) CDC-IgG-negative women showed a positive FC cross-match against the husband or offspring lymphocytes. Flow-PRA analysis confirmed that 9 of 10 positive cross-matched sera contained anti-HLA IgG. Among the 43 transfused patients, 11 of 16 (68.7%) of the women who were CDC-IgG-positive after blood transfusion showed FC-detectable IgG before transfusion; although 2 of 27 (7.4%) of the patients who remained CDC-IgG-negative after transfusion showed FC-detectable IgG before transfusion (P <0.001).

Conclusion: Most of the de novo anti-HLA immunizations detected by CDC after transfusion in previously pregnant women can be detected by Flow-PRA before transfusion.