Lecture 5 - Alloantibodies

Question 1

what is an alloantibody?

Answer 1

an antibody formed in response to a sensitising event

Question 2

what are examples of alloantibodies?

Answer 2

Kell, cellano, duffy

Question 3

what groups of antibodies are the most concerning?

Answer 3

IgG and IgM

Question 4

what are the differences between IgG and IgM?

Answer 4

IgG can only cross placenta, IgM has lower optimal temperature and a higher immune response

Question 5

what is the mechanism of an acute haemolytic reaction?

Answer 5

the activation of complement or the action of macrophages in a response to an alloantibody

Question 6

how does complement activation cause an acute haemolytic reaction?

Answer 6

the final steps in the pathway initiate haemolysis of the red cells

Question 7

what is involved in the clinical phase of haemolytic shock?

Answer 7

lysis of red cells causes free haemoglobin and remnants of red cell membrane, activation of coagulation cascade which causes DIC

Question 8

what are the symptoms of haemolytic shock?

Answer 8

hypotension due to lack of red cells, vasodilation, tachycardia to maintain bp, rapid and shallow breathing due to stimulation of sympathetic nervous system, chest and lumbar pain

Question 9

what is phase 2 of acute haemolytic shock?

Answer 9

post shock, evidence of haemolysis

Question 10

what are the features of phase 2?

Answer 10

haemoglobinuria, drop in Hb, raised bilirubin, jaundice

Question 11

what does the blood film of blood in stage 2 of acute haemolytic anaemia look like?

Answer 11

shows agglutination, spherocytes and red cell fragments

Question 12

what is stage 3 of acute haemolytic anaemia? what happens?

Answer 12

oliguric, free Hb in the blood causes toxic acute tubular necrosis which leads to acute renal failure

Question 13

what is stage 4 of acute haemolytic anaemia?

Answer 13

diuretic, renal tubules remain scarred causing loss of potassium, electrolyte imbalance, spontaneous urination

Question 14

what is a delayed haemolytic reaction?

Answer 14

the mechanism of macrophages mainly in the spleen which monitor the red blood cells for IgG antibodies

Question 15

what two actions can the spleen take if they detect an IgG antibody?

Answer 15

remove the cell from circulation or remove the part of the membrane with the antibody which forms spherocytes

Question 16

what is extravascular haemolysis?

Answer 16

the action of the spleen on red blood cells

Question 17

what antibodies are associated with delayed transfusion reactions?

Answer 17

Jk antibodies

Question 18

what antibodies increase in titre following 1st exposure?

Answer 18

IgM followed by IgG, second exposure is larger amount of IgG

Question 19

what is eluate?

Answer 19

strong acid is used to remove the antibodies from the red cell so that they can be identified

Question 20

why can’t IgG antibodies be used for ABO grouping?

Answer 20

they cannot bridge the zeta potential between two red cells as they carry a slight negative charge

Question 21

what would you do to ABO group if you only have IgG antibodies?

Answer 21

perform an indirect Antiglobulin test

Question 22

how does an indirect anti globulin test work?

Answer 22

serum and red cells mixed and washed to remove unbound antibodies, anti-human antibody added that will bind to two antibodies if present, and if they are present this will cause agglutination of red cells

Question 23

what are antibody screening cells?

Answer 23

red cells that express specific antigens so that they can be mixed with patient plasma to detect alloantibodies

Question 24

what is the dosage effect?

Answer 24

a stronger reaction occurring with homozygous antigen expression as opposed to heterozygous

Question 25

what does papain do?

Answer 25

enhances reaction with Rh system antibodies and Kidd system antibodies, destroys antibodies associated with MNS and Duffy system

Question 26

how can autoantibodies cause false positive reactions?

Answer 26

autoantibodies react positively with all antigens

Question 27

how can identification of an antibody be conformed by phenotyping?

Answer 27

if a patient expresses an antibody then it should be antigen negative for that antibody