Humoral immunomodulatory effect of influenza vaccine in potential blood donors: implications for transfusion safety

Background: Generalised immune stimulation may follow vaccination causing increased antibody titres of nonvaccine-related antibodies or bystander antibodies, including those to human leukocyte antigens (HLA) and ABO blood group antigens. HLA antibodies may lead to transfusion-related acute lung injury. High-titre ABO antibodies may cause acute haemolytic transfusion reactions after plasma-incompatible platelet transfusion. It is unknown if these antibodies can be stimulated by vaccination in otherwise normal subjects. Methods: Blood samples of healthy volunteers who received the 2009 influenza vaccine were analysed for HLA and ABO antibodies before and 14 days after vaccination (n = 86). Age, gender and history of exposure to foreign tissue, through pregnancy, blood transfusion or tissue transplant were collected. Results were analysed with descriptive statistics, paired t-test and chi(2) test. Results: There was no increase in HLA or ABO antibody levels after vaccination (P = not significant). Forty per cent of subjects (n = 35) had previously formed HLA antibody and 16% (7 males and 7 females) had HLA sensitisation but did not report foreign tissue exposure. The average panel reactive antibody of the HLA sensitised but nonexposed subjects was lower in males than females (3.4 and 28.6%, respectively, P = 0.015, t-test), suggesting that some females may have had unrecognised pregnancy. Conclusions: HLA or ABO antibodies did not appear to be stimulated by the 2009 influenza vaccine. Female blood donors with putatively unrecognised pregnancies may have higher risk for HLA sensitisation than previously thought. Further study using different vaccine formulations may lead to better understanding of the risks of bystander antibodies in the blood donor population.