Incidence and risk factors of anti-HLA immunization after pregnancy.

Pregnancy is the only natural source of anti-HLA immunization. The exact frequency of this immunization remains undetermined as prior studies either used methods with a low sensitivity or were performed late after delivery. We present here the first study on women at delivery evaluating anti-HLA immunization by Luminex. We also attempted to isolate factors influencing immunization, such as soluble HLA-G (sHLA-G) levels and genetic polymorphisms. With Luminex, anti-HLA immunization was observed in 54.4% of the women. As expected, immunization frequency increased with the number of children, reaching 74% in women with >2 deliveries. Among immunized women, strong cytotoxic Ab (as detected by Complement Dependent Cytotoxicity) were associated with a lower level of sHLA-G. None of the studied polymorphisms influenced immunization rate in the whole cohort. Among 94 first pregnant women with no history of miscarriage, the -174 IL-6 gene promoter mutation (G/C) appeared more frequently in non immunized women (69% vs. 45% in immunized ones, p=0.02). Lastly, the occurrence of a miscarriage before the first live delivery significantly decreased immunization. These results may help to understand mechanisms of pregnancy induced immunization. They also have an impact in the management of previous pregnant women requiring organ or hematopoietic stem cell transplantation.