Introduction: The human leukocyte antigen system, shortly HLA, is the most polymorphic genetic system in humans and represent the main immunologic barrier for kidney transplantation. Previous transplants, blood transfusions and/pregnancies may induce formation of antibodies against mismatched HLA molecules defined as HLA alloimmunization. It can cause allograft injury and may contribute to recipient morbidity and mortality. 

Aim: We wanted to test how transfusions interact on the immunization process. Patients who are highly immunized face more graft rejection, shortened graft survival, longer waiting times on organ allocation programmes as they meet with difficulty and delay in finding an HLA compatible graft.

Material and methods: The awareness that leucocytes are the major cause of HLA immunization fostered the development of methods which reduce the leucocytes from blood samples. Due to clinical relevance of HLA specific antibodies serum samples from potential kidney recipients were screened every three months. The methods for determining the presence and specificity of HLA antibodies that we used were the Complement Dependent Cytotoxicity Assay and the Luminex method. 

Results: The risk of immunization by transfusions has to be evaluated in the context of the immunologic history of the patient, as they are down-regulatory in naive recipients and stimulatory in patients previously exposed to alloantigens. Filtration is a method for leukocyte depletion and it removes 99.99% of leukocytes from blood unit. Every blood cell express HLA molecules, so even leukocyte depleted blood unit can elicit immune response and HLA immunization.

Conclusions: The most frequent sensitising events in potential kidney recipients are the blood transfusions. Avoidance of transfusions whenever is possible remains the key strategy as the risk of HLA immunization even from leukodepleted blood units, remains a significant risk.