National Neutrophil Laboratory

Alloimmune neonatal neutropenia (ANN) – an uncommon condition where a newborn may present with bacterial infection(s) due to neutropenia in which destruction of neutrophils occurred by maternal allo-antibodies to specific human neutrophil antigens (HNAs).

Autoimmune neutropenia (AIN) is a disorder most common in infants and young children where the body makes IgG antibodies directed against neutrophil antigens which results in neutrophil clearance. When neutropenia is the only blood abnormality detected, it is also known as primary autoimmune neutropenia.

Transfusion-related acute lung injury (TRALI) is acute lung injury (ALI) that usually develops within 6 hours after the transfusion of any blood component. The incidence of TRALI is approximately 1:4000 transfusions.  Clinical features include acute onset of hypoxemia, tachypnea, cyanosis, fever, hypotension and radiographic evidence of bilateral pulmonary infiltrates in the absence of circulatory overload.  The mechanism of immune TRALI is associated with the activation of neutrophils located in the pulmonary capillary vasculature due to the passive transfer of leukocyte antibodies found in transfused blood components, or on rare occasions leukocyte antibodies in the recipient.  The mechanism of “non-immune TRALI” is the transfusion of cytokines and soluble biologically active lipids found in cellular blood components.  In cases of suspected TRALI, testing of plasma from implicated donors and recipients is critical.

Laboratory investigation of TRALI

The National Neutrophil Immunology Reference Laboratory has been performing  leukocyte antibody testing in suspected transfusion reactions since TRALI was first described by Popovsky and Moore in 1985.  As recommended by the International Granulocyte Immunology Workshops (IGIW), we use a combination of the granulocyte immunofluorescence test (GIFT) and the granulocyte agglutination test (GAT) when detecting and identifying neutrophil antibodies.  Results obtained from the IGIW have confirmed that GAT is an essential technique when detecting agglutinating antibodies such as HNA-3a which has have been associated with severe and multiple fatal cases of TRALI.  Two IGIW assessments have included HNA-3a antibodies where laboratories using GIFT alone failed to detect antibody to HNA-3a in samples involving TRALI fatalities.  Because both techniques are rarely offered in reference laboratories, it is essential to identify laboratories that routinely offer a combination of GIFT and GAT when detecting neutrophil antibodies.  Our laboratory also offers state of the art bead based flow cytometry assays to detect and identify HLA Class I and Class II antibodies.

Drug-induced neutropenia can be mild, moderate, or severe.  Severe neutropenia absolute neutrophil counts (ANC) less than 100 neutrophils/µL) are rare and associated with life-threatening and even fatal infections. Mild or moderate drug-induced neutropenia (ANC of 500-1000/ µL) may evolve slowly and may resolve spontaneously. Drugs known to be involved in immune-mediated neutropenia include antibiotics, analgesics, antiarrhythmias, antimalarials and antithyroids.

• In general the official gene name is followed by an asterisk and by a two digit allele number.  Genetic variations of standard alleles are numbered consecutively and are not extended by a third or fourth digit.
• New alleles are numbered consecutively according to the first publication.
• Only missense mutations within exons leading to an amino acid exchange are included.

• Granulocyte antigens will be called HNA (human neutrophil alloantigen).
• The antigen nomenclature is based upon the serologically defined epitope(s) on glycoproteins.
• The glycoprotein (antigen system) is coded by a number: HNA-1, HNA-2, etc.
• The phenotypic variation of the antigen is assigned given in lower case letters: HNA-1a, HNA-1b, etc.
• HNA-2 is an isoantigen without allelic variation and therefore should be named HNA-2.
• Glycoproteins, which are encoded by one allele can exhibit more than one epitope.  For example, HNA-1b and HNA-1c are encoded by FCGR3B*03 on glycoprotein FcγRIIIb (CD16).
• One epitope can be encoded by different alleles.  For example, HNA-1a is encoded by FCGR3B*01 and FCGR3B*04.
• Only slightly altered epitopes can be identified by adding the subscript “var” in cases which antibodies specific for the original epitope bind with reduced affinity of altered reactivity pattern.  For example, HNA-3a_var for HNA-3a with an additional Leu151Phe exchange.
• The cellular expression of HNA is not necessarily restricted to neutrophil granulocytes.  For example, HNA-3 is expressed on neutrophils, lymphocytes, platelets and tissues.
• Antigens originally identified on other cell types and whose main clinical impact depends on cells other than neutrophils keep their original nomenclature and are not included in HNA nomenclature.  For example, Naka (GPIV, CD36) located on platelets and monocytes.

## HNA-1d is antithetical to HNA-1c

**HNA-4b is actually under investigation

NT = Not Tested