Blood Bank: HLA

• Chromosome 6

• Major histocompatibility complex (MHC)

HLA molecules are found in a “region” (consists of approximately 250 genes) found on (——), this “region” is called the (——), which is inherited as a chromatid haplotype from each parent

Crossover

Sometimes a recombination of HLA genes between haplotypes will occur causing a phenomenon called (——)

locus

In HLA nomenclature, the (——) is designated first followed by a number

• T lymphocytes

• Platelets

• Tissues and organs

Which cells have HLA Ags

• Class I: A, B, C

• Class II: DR, DQ, DP

• Class III: diverse molecules (e.g., C’ factors, TNF, etc.)

(Class I and II are relevant to BB testing and transplantation)

Describe the different regions of HLA and the loci associated with each

Linkage disequilibrium

The associations between HLA gene alleles that occur more frequently than would be expectd by random assortment in the population, e.g., if HLA-A1 and HLA-B8 expected random assortment were 1.6% in certain populations, this haplotype would actually occur in 8% of the population

• CD8 T cell

• ⍺ chain and β-2-macroglobulin

• Nucleated cells and platelets

HLA Class I characteristics (Ag presentation, components, expressed on which cells (2))

• CD4 T cells

• ⍺ chain and β chain

• B lymphs, macrophages, monocytes, and dendritic cells

HLA Class II characteristics (Ag presentation, components, expressed on which cells (4))

• Pregnancy

• Blood transfusion

• Transplantation

Most common stimulation of HLA allo-Ab comes from (——) while the second most common source is (——); the highest risk for developing HLA allo-Ab is through (——) (70% of patients within 5 years)

LR blood products that contain WBCs

Reduction of HLA allo-Ab stimulation is through the use of…

• IgG

• Antibody mediated rejection (AMR)

HLA allo-Abs are commonly (——) and can activate C’ and/or become opsonized, which can lead to (——)

• Cross reactivity

• Cross reactive groups (CREGs)

HLA allo-Abs can exhibit (——), where an Ab directed against 1 HLA Ag determinant can react with other HLA Ags when they share a structural element; these Ags that share certain structures are called (——)

• Flow cytometry

• Multiple single Ag Bead immunoassay (SAB)

• Virtual crossmatch

3 common ways of testing for micro lymphocytotoxicity

• allele-level HLA genotyping

• Serological Ab-Ag

For hematopoietic stem cell transplants, a high resolution (——) is used oto help minimize recipient GVHD; for solid organ transplantation and for transfusion, a (——) test is used to help minimize rejection

• Sequence specific oligonucleotides (SSO)

• Sequence specific primers (SSP

• DNA sequence based typing

3 common HLA typing assays used in blood bank (3)

Sequence specific oligonucleotides (SSO)

Test involves PCR amplification of the HLA gene regions using (generic) primers to conserve DNA sequencing flanking the region (sequence detected by oligonucleotide probe hybridization)

Sequence specific primers (SSP)

Test involves using oligonucleotide primers to target specific DNA sequences that identify specific HLA alleles

DNA sequence based typing (SBT)

Direct nucleotide sequencing of HLA genes is used. There are two methods used: 1) Sanger based DNA sequencing, 2) Next generation DNA sequencing (NGS)

Transfusion related acute lung injury (TRALI)

Donor HLA Abs to recipient WBCs is associated with which transfusion reaction; associated with donor allo-typing HLA Abs of class I and II

• Relationship/paternity

• Disease association (susceptibility)

• Platelet refracroriness

• TRALI

• TA-GVHD (T cells → immunocompromised. pt)

Initially, the HLA system plays a primary clinical significance in transplantaion, but recently it has become of interest in the genetics and disease association arenas like… (5)

• HLA-DR

• HLA-A, B, C

Hematopoietic stem cell transplantation requires matching of (—4—) in both the transplant recipient and the donor

• ABO

• HLA-DR

• HLA-A, B, C

Solid organ transplantation requires matching of (—5—) in both the transplant recipient and the donor

• Kidney

• Heart

• Lung

• Liver

• Pancreas and Islet cell

Examples of solid organ transplants (5)

• HPA-1

• HPA-2

• HPA-3

• HPA-4

• HPA-5

• HPA-15

There are approximately 41 HPAs, but 6 are regarded as “most clinically relevant” due to their allele frequency in the Caucasian population, expression levels, and immunogenicity. These 6 HPAs are…

• HPA-1 → GPIIIa

• HPA-2 → GPIb

• HPA-3 → GPIIb

• HPA-5 → GPI

(HPA-15 is on CD109)

What are the glycoprotein locations of HPA 1, 2, 3, and 5?

• Platelet transfusion refractoriness

• Post transfusion purpura (PTP)

• Feto-neonatal alloimmune thrombocytopenia (FNAIT)

Immunization against HPAs from repeated PLT transfusions or feto-maternal stimulation will result in subsequent PLT Ab production, which may lead to… (3)

• Glanzmann thrombasthenia (GT)

• Bernard Soulier Syndrome (BSS)

HPA immunization can also occur from (conditions)… (2)

HPA-1a

About 80% of PLT Abs detected are…

• Monoclonal antibody specific immobilization of platelet antigen (MAIPA)

• ELISA

• Solid phase PLT Ab tests

How are HPA Abs detected? (3)

“fresh” PLTs

The MAIPA test is highlt specialized where it is very labor intensive and requires the used of (——); only special labs perform this specific test

< 5000/µL

Platelet transfusion refractory is suspected if the 1 hour post transfusion corrected count increment (CCI) is…

• Sepsis

• Fever

• Infection

• Bleeding

• Drugs (vancomycin, amphotericin B, etc.)

• Splenic sequestration

• GVHD

Non immune causes of platelet refractoriness (7)

• HPA-1a Ab

• HLA class I Ab

• ABO mismatched PLTs

• Abs against drug-platelet glycoprotein complex

Immune causes of platelet refractoriness (4)

• Multiparous women

• HPA-1a Ab (sometimes HPA-1b)

Post transfusion purpura frequently occurs in (——) and (——) is the most common cause

• 5-10 days

• 21 days

Post transfusion purpura (PTP) has an abrupt onset of severe thrombocytopenia (<10,000/µL) in (——) post transfusion, but it is usually self limited where recovery is seen within (——)

• Purpura and bleeding

• High dose IV IgG or therapeutic plasma exchange (TPE)

The signs of post transfusion purpura are (—2—) and the treatment for this condition is (—2—)

• HPA-1a

• Internal bleeding

• Disabilities or death

Feto-neonatal alloimmune thrombocytopenia (FNAIT) is most commonly caused by (——); (——) can occur due to severe thrombocytopenia, and can eventually lead to (—2—)