2020B14 Briefly outline the potential immunological effects of transfusing packed red cells.

Immediate:

Febrile non-haemolytic	· Donor blood storage -> cytokine accumulation (IL-1, IL-6, TNF-α) · Fever, malaise, dyspnoea · Not harmful
Febrile haemolytic	· Due to incompatible transfusion · RBC > platelets > FFP · (Normal) prior alloimmunisation due to molecular mimicry by gut flora · Donor antigen vs recipient antibody · ABO IgM-> intravascular haemolysis (DIC, renal failure, death) · RhD IgG-> extravascular haemolysis (haemolytic anaemia)
Anaphylaxis	· Type 1 hypersensitivity · FFP and platelets > RBC · Donor protein vs recipient IgE · Especially IgA vs IgA-deficient host · Mast cell degranulation -> vasodilation, bronchospasm, angioedema
TRALI	· Transfusion-related acute lung injury · FFP and platelets > RBC · ? Donor antibody vs recipient lung antigen · ? Illness-related priming of neutrophils and endothelium · Non-cardiogenic pulmonary oedema · Major cause of mortality · FFP and platelets > others · Onset during transfusion or < 6 hours

Alloimmunisation

· First exposure to antigen during transfusion or childbirth

· Alloantibodies produced

· Second exposure results in antibody-mediated destruction

Delayed haemolytic reaction:

· Especially if recurrent transfusion

· Antibodies: Kell, Kidd, Duffy

· Diminishing antibody titre -> re-exposure -> anamnestic response

· Extravascular haemolysis -> haemolytic anaemia

Haemolytic disease of the newborn:

· RhD+ foetus vs RhD- mother; or Kell(+) foetus vs Kell(-) mother

· IgG crosses placenta -> severe haemolysis

· Prevented by anti-D at 28/40 and 34/40 in RhD- women

Post-transfusion purpura:

· Donor platelet vs recipient alloantibodies

· Consumption of both donor platelets and bystanders

Immunomodulation

· Mechanism unclear - ? donor WBC or mediators

· ↑Post-op infection, ↑cancer recurrence

· Rationale for cell salvage use in major cancer surgery

Graft vs host

· Donor WBC multiplies in immunocompromised host -> tissue damage

· Affects skin (rash), marrow (suppression), liver (↑LFT), GIT (diarrhoea)

· Rare, fatal, untreatable

· Prevented by gamma irradiation of blood product