Platelet Allo-Antigens Flashcards
surface receptors and antigens on platelets
HPA (human platelet allo-antigens)
class I HLA
ABO
T or F. HP1b is more common than HP1a
F! “a” is more common/frequent
methods used to detect HPA antibodies
Luminex
- PakLX assay
among others
treatment of FNAIT
transfusion with maternal washed PLTS - preferably apheresis or compatible PLTs is antibody specificity unknown
unrelated HPA typed donors are often used
> randome PLT units may result in successful increments
percutaneous umbilical blood sampling (PUBS) can be performed to monitor PLT count in utero (and transfuse)
treatment of mom with IVIg during pregnancy
> IVIg therapy in baby has had mixed success
treatment of PTP
IVIg
corticosteroids
platelet transfusion
> transfusion of HPA compatible platelts when possible
plasmapheresis
in future, use of HPA matched units and IVIg pre-transfusion
GPIIb/IIIa
when activated, binds natural ligands and causes aggregation
= fibrinogen, Vitronectin, fibronectin, vWF
HPA alloantigens on both GPIIb/IIIa subunits that are screened for in Ab tests
- GPIIb = HPA-3
- GPIIIa = HPA-1,-4
this binds collagen and takes part in adhesion + activation
GPIa/IIa
HPA ALLOANIGENS ON GP1A ONLY
HPA-5
vWF receptor
GP1b/V/IX
how do antibodies to non-self platelet antigens develop?
after exposure to non-self platelet HPA following transfusion and pregnancy
what is FNAIT
fetal/neonatal allo-immune thrombocytopenia
- mom develops IgG Abs to baby’s plt allo-antigens
- passive thrombocytopenia (can occur in utero)
T or F. FNAIT occurs in first pregnancy
T
T or F. FNAIT is self-resolving
once baby is born, source of Abs (mom) is cut off
- thrombocytopenia 1-3 wks post-partum
lab detection of HPA Abs in FNAIT
- Ab screen in maternal serum
> during gestation if previous pregnancy was affected - HPA alloantigen typing of mom and dad
most common HPA antibody detected
anti HPA-1a
T or F. FNAIT lab detection is quantitative
F! Ab screen not quant but different sample dates can be tested in parallel for estimate of titre changes
methods for HPA Ab detection
platelet immunofluorescence (PIFT-FFC); read by flow
solid phase adherence assay (SPAA)
antigen capture ELISA (ACE)
monoclonal antibody-specific immobilization of platelet antigens (MAIPA)
Luminex (PakLX assay)
describe the Luminex screening/ID test
- uses phycoerythrin (PE) labelled anti-human IgG to detect antibodies bound to plt antigens on the beads
- amt of fluorescence detected (MFI) determines whether bead is + or -
- which Abs are present is determined by combination of beads that are reacting in the panel
what is the follow up done to antibody ID Testing?
HPA genotyping
> LinkSeq HPA typing kits (qPCR)
if HLA class I detected = Ab specificity and typing
describe HPA typing by qPCR
- specific DNa sequences amplified while also being quantified by spectrofluorimetric methods
=> Sybr Green = dsDNA binding fluorescent molecule - amplified product is then heated to identify melt curve characteristics that determine the presence/absence of HPA antigen
PTP
post transfusion purpura
- are event = acute episode of severe immune thrombocytopenia after ~1wk post-transfusion
- amnestic response to previous exposure to platelet allo-antigens
T or F. PTP more frequent in adults
T, more in females
T or F. PTP is self-resolving
T, but can be fatal
