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4.1 Transfusion and Transplant Immunology > Ii and P blood Group > Flashcards

Ii and P blood Group Flashcards

1
Q

Talk about the I and i antigens

A

They are both considered uncompleted ABH active chains

i is linear/non branched -> adds on last 2 sugars but in a straight line

All cord blood is i+ I-, i is gradually converted to I as we age

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2
Q

What blood group has the most I antigen sites

A

Bombay -> no H antigen at all -> therefore lots of unfinished chains

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3
Q

Talk about the genetics of the I/i system

A

I and i genes found on chromosome 6

Their products are transferase enzymes that attach repeating units of Gal and GlcNAc to the ABO Precursor substance

Big I gene encodes for branching of the polysaccharide

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4
Q

Talk about the presence of i vs I, frequency etc

A

i gradually converted to I within the first 18 months of life

Not all is converted to I, some still prsent on adult cells

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5
Q

Talk about anti-I

A

Its a common cold autoantibody

We used to use cord blood to identify these (i positive)

but we were unsure if cord blood was HIV negative so we switched over to adult little i to test cells in lab etc

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6
Q

Where are the Ii antigens found?

A

Saliva
Human milk
On leukocytes
On platelets
In amniotic fluid
Urine

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7
Q

How are I/i antigens affected by enzymes?

A

Enhanced by enzyme treatment

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8
Q

When might you see i in adults?

A

i antigen persisting into adulthood without conversion to I is very rare

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9
Q

Talk about anti-I antibody

A

Common autoantibody -> nearly everyone has a cold reactive anti-I -> but its IgM and only reactive at low temps so not clinically significant

It will react with virtually all adult red blood cells but not cord cells

Used to cause unwanted positivity in DAT in donor units

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10
Q

Talk about anti-I DAT interference, how do we avoid this?

A

Nearly everyone has an anti-I antibody that reacts at cold temperatures

This doesnt cause any problems in patient but will cause complement binding when donor packs are refrigerated

We now use monospecific IgG AHG (wont pick up IgM anti-I) because of this

DAT+ unit -> then do IgG vs complement -> if complement only not concerned

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11
Q

How do we investigate an alli anti-I, which are clinically significant

A

Can remove by pre-warming everything or reduce activity

Cold technique will enhance any weak reactions

If anti-I reacts at 30 degrees and titre is greater than 1000 then antibody is pathologic

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12
Q

Talk about pathologic anti-I

A

Reactive at 30 degrees and titre > 1000

Wide thermal range of reactivity and high titre -> will react at 4 degrees and higher temps (30)

Good at complement binding

This is true cold agglutinins disease

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13
Q

What causes pathologic anti-I

A

Cold agglutinin syndrome secondary to M. pneumoniae infectons

anti-i in IMS???

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14
Q

What do we do with a pathoogic anti-I in the lab?

A

These will be pan reactive
Can mask clinically significant allo-antibodies
-> auto adsorption may be necessary to remove reactivity

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15
Q

How do we carry out cold adsorption for investigation of anti-I

A

We use REST - rabbit erythrocyte stroma ___
-> lysed rabbit rbcs, conventraed stroma
-> cells covered in H and I antigens

Incubate patient plasma with these REST cells and then spin down

Take off plasma and test again

Auto-reactivity decreases with each cycle

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16
Q

How do we carry out cold adsorption for investigation of anti-I

A

We use REST - rabbit erythrocyte stroma ___
-> lysed rabbit rbcs, conventraed stroma
-> cells covered in H and I antigens

Incubate patient plasma with these REST cells and then spin down

Take off plasma and test again

Auto-reactivity decreases with each cycle

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17
Q

What is ati-IH, where is it found?

A

Found in the serum of A1 phenotype

These antibody will reacts strongly with RBCs high in H as well as I antigens

Reacts strongly with O cells

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18
Q

Talk about anti-i

A

Fabian has never seen this

Antibody will react with cord cells

IgM antibody - reacts best at 4 degrees

Potent auto anti-i in children with IMS
- transient

19
Q

Talk about the history of the PIPK system

A

Landsteiner and levine discovered anti-P first in 1927

20
Q

What antigens are part of the PIPk system?

A

P1 and Pk

21
Q

Talk about the genetics of the PIPK system

A

Locus is on chromosome 22

Gene encodes enzymes that suquentially add sugars to precursor subatance -> related to ABO, Le and Ii systems

22
Q

What antigens are part of the GLOB system

A

P and p

  • p is the amorph of P and was originally called Tj(a)
23
Q

Where is the GLOB locus

A

Chromosome 3

24
Q

Talk about the expression of PIPK and GLOB antigens

A

All antigens (P, Pk and P1) are expressed in glycosphingolipids on rbcs, not in glycoproteins

Antigens are built through the addition of sugars to precursor glycosphingolipids, analogous to A, B and H antigens

25
Q

Talk about expression of P1 antigens

A

P1 antigens are built y adding Gal in a alpha(1->4) linkage to the same precursor substance (paragloboside) as H, A, B, I and i antigens are built

26
Q

Where is P1 antigen found and why?

A

Only found on red cells as type 2 chains needed

Millions of copies on red cell

27
Q

What is complicated about the genetics of PIPK and GLOB antigens

A

Chr 22 and 3 involved in formation of antigens
Some overlap between these

28
Q

Talk about the frequency of P and p

A

Vast majority of people are P+
p similar to Bombay -> as your both blood group negative

P and PIPK are separate blood group systems but both rely on similar base structure
-> if p then equivalent to Bombay
-> these produce an anti-PIPPK

29
Q

What are the enzymes resposible for P1, PK and P

A

P1 and Pk = alpha4GalT1
P = B3GalNAcT1

30
Q

What is the basic precursor structure for Pk, P1 and P

A

Cerimide = basic sugar on rbc
Cetrimide + glucose
GlcCer -> LacCer

LC3 -> P1
OR
LacCer -> Pk -> P

31
Q

Talk about P2

A

Theres no P2 antigen it is just a lack of P1
-> P2 individuals produce an anti-P1

32
Q

Talk about P2

A

Theres no P2 antigen it is just a lack of P1
-> P2 individuals produce an anti-P1

33
Q

If P2 individuals lack a P1 how can they still have a pK

A

This is due to splice variants in the alpha galatsoyl transferase enzyme -> P2 are not deficient in the enzyme they just have a modified version

This splice variant favours making Pk and not P1

Splice variants are quite common but deficiency very rare

34
Q

Talk about the p phenotype

A

These lack P, P1 and Pk

Called p phenotype

These produce an anti-P, P1 and Pk

35
Q

Talk about anti-P1PkP

A

igG antibody
Very strong
Can cause HDFN
Everything in panel comes up positive but auto negative
Rare but IBTS got one last year

36
Q

Talk about the Pk phenotype

A

Only the second enzyme missing in chain i.e. still have Pk and P1
P-
-> anti P1 produced

37
Q

PIPK Antigen frequencies in Caucasians

A

P1 = 79%
P2 = 21%
p = rare
P1k = very rare
P2k = most rare

38
Q

PIPK frequencies in Blacks

A

P1 = 94%
P2 = 6%
p = rare
P1k = very rare
P2k = most rare

39
Q

What are the general characteristics of the P1 antigen

A

Deteriorates durin storage - similar to dufy in that you might need to use fresh panel if query an anti-P1

Variable antigen expression between individuals -> often graded on antibody panels (1-5)

Not well developed at birth -> no HDN

40
Q

Talk about anti-P1

A

Found in P2 phenotype
Weak, cold reacting antibody
IgM antibody that reacts best <25
Naturally ocuring
Enhanced with enzymes
Causes problems in reverse group or room temp crossmatch

41
Q

Talk about allo anti-P

A

Allo anti-P is naturally occuring in Pk phenotype (rare)

Its clinically significant

Can cause HDN and HTR

Complement activation at 37 degrees

42
Q

Talk about auto anti-P

A

IgG found in PcH

Called the Donath-Landsteiner antibody

Biphasic haemolysin: binds complement at cold tem and activates complement in warm temo to lyse red blood cells

Fouond in children <14 following viral infection and in tertiary syphilis

43
Q

Talk about auto anti-P

A

IgG found in PcH

Called the Donath-Landsteiner antibody

Biphasic haemolysin: binds complement at cold tem and activates complement in warm temo to lyse red blood cells

Fouond in children <14 following viral infection and in tertiary syphilis

4.1 Transfusion and Transplant Immunology (24 decks)

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