Granulocytes are integral components of both the innate and adaptive immune systems. Based on the variations in their staining properties, granulocytes are further subdivided into neutrophila, basophils and eosinophils. Because of the fact that neutrophils constitute >99% of the granulocyte population, the terms "granulocyte" and "neutrophil" are often used interchangeably used in granulocyte immunology. Precisely, the family of glycoprotein epitopes expressed on granulocytes have been collectively named as the human neutrophil antigens (HNAs). Random estimation of prevalence of these antigen frequencies in various populations have shown striking differences. Currently, there are fourteen (14) HNA alleles across five antigen systems namely HNA-1 through HNA-5 recognized and approved by International Society of Blood Transfusion - Granulocyte Immunology Working Party (ISBT-GIWP). Antibodies that recognize these epitopes have been associated with neutropenia, transfusion complications, haematopoietic stem cell transplant nonengraftment and renal transplant rejection.

The genes underlying their molecular mechanisms were identified as FCGR3B, CD177, SLC44A2, ITGAM and ITGAL, respectively.