Human neutrophil antigen-3a antibodies induce neutrophil aggregation in a plasma-free medium.

Background: Antibodies against the human neutrophil alloantigen-3a (HNA-3a) are involved in severe cases of transfusion-related acute lung injury (TRALI), but the susceptibility of patients towards HNA-3a antibody differs largely. HNA-3a antibodies induce granulocyte aggregation. However, it is unresolved whether plasma proteins are required for granulocyte aggregation.

Materials And Methods: We investigated whether HNA-3a-antibody-induced aggregation of polymorphonuclear cells is dependent on plasma factors by using and modifying the granulocyte agglutination test (GAT).

Results: Polymorphonuclear cells homozygous for HNA-3a did not aggregate when incubated with HNA-3a antibodies in a plasma-protein-free GAT setup. When the GAT was performed using polymorphonuclear cells re-suspended in phosphate-buffered saline containing proteins, HNA-3-mediated aggregation was observed. Moreover, using Tween® 20 for blocking the plates, reconstituted the granulocyte aggregation in a protein-free medium. This indicates that granulocyte aggregation probably occurs by direct granulocyte-granulocyte interaction(s) or is mediated by substances released by neutrophils after activation.

Discussion: Granulocyte aggregation induced by HNA-3a antibodies does not require human plasma proteins. Interindividual variability in the response to HNA-3a antibodies does not depend on differences in patient's plasma proteins.