Neutrophil Antigens
Nowadays, five antigen systems are defined on human granulocytes. They are named as "Human Neutrophil Antigens" or "HNA"-1 to -5. The first characterization of a neutrophil specific antigen was made by Lalezari in 1960, who described a case of Neonatal Immune Neutropenia (NIN) caused by "NA1" ("Neutrophil Antigen 1", today HNA-1a). This antigen is located on the clinically most important immunogenic glycoprotein of the neutrophil, Fc gamma receptor IIIb (CD16b). There are two further antigens located on this receptor, HNA-1b and HNA-1c. Neutrophil autoantibodies bind preferably to granulocytes expressing the HNA-1a antigen.
| antigen | old nomenclature | localisation | frequency % | comment |
|---|---|---|---|---|
| HNA-1a HNA-1b HNA-1c |
NA1 NA2 SH |
Fcγ Rezeptor IIIb = CD16b | 58 88 5 |
granulocyte-specific |
| HNA-2a | NB1 | NB1 GP = CD177 | 97 | granulocyte-specific |
| HNA-3a | 5b | GP 70-95 | 97 | also expressed on lymphocytes |
| HNA-4a | Mart | CD11b | 99 | granulocyte-specific |
| HNA-5a | Ond | CD11a | 92 | also expressed on lymphocytes |
HNA-2a, the former NB1, is also located on a granulocyte-specific glycoprotein, CD177. Its exact function is still unknown, but recent studies revealed that CD177 acts as a counterreceptor for endothelial PECAM-1 (CD31) and therefore might be involved in neutrophil transmigration (Sachs et al., J Biol Chem 2007;282:23603-23612). A special feature of this antigen is its heterogeneic expression, i.e. there are two subpopulations of granulocytes in one individual, HNA-2a-positive and HNA-2a-negative granulocytes, respectively.
Antibodies against HNA-3a, the former 5b, are often detected in cases of severe transfusion-associated acute lung injury (TRALI). The molecular basis of this antigen is still subject of research. HNA-4a and HNA-5a are high frequency antigens localized on integrins. They are results of single nucleotide polymorphisms. Antibodies directed against the proteins coded by the antithetic alleles were not described so far.
