Immunohematology Handout

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De La Salle Health Sciences Institute DEPARTMENT OF PATHOLOGY IMMUNOHEMATOLOGY

• The study of immunologic reactions involving all components of blood • Deals with antigens, antibodies and antigen-antibody reactions

Application

 transfusion of blood & its components

 diagnosis, prevention & management of immunization associated with pregnancy

 leukocyte testing for organ transplantation  laboratory resolution of parentage problems DEFINITION OF TERMS

 ANTIGEN (Ag)

 Any substance that stimulates the production of antibodies  AGGLUTINOGEN

 Antigen on the surface of RBCs  ANTIBODY (Ab)

 Proteins produced by the Reticuloendothelial system in response to antigen stimulation

 AGGLUTININ

 Antibody that attacks RBC Antigens and manifests this activity by clumping of the RBC

 HEMOLYSIN

 Abs that attack RBC Antigens and manifests this activity by lysis of the RBCs

 AGGLUTINATION

 Clumping of red blood cells as a result of antibodies binding to antigenic sites of adjacent red cells

 NATURAL ANTIBODIES

 Abs that appear without antigenic stimulation, during childhood, decreases with age

 ACQUIRED/ IMMUNE ANTIBODIES

 Appear upon introduction of Ag by disease, transfusion, pregnancy, and substances chemically related to RBC Antigens  COMPLETE ANTIBODIES

 Bivalent Antibodies

 will directly agglutinate appropriate RBCs  INCOMPLETE ANTIBODIES

 Univalent Abs

 coats RBC surface but cannot directly agglutinate them  ISOANTIBODIES / ALLOANTIBODIES

 Abs produced against Ags from genetically different individuals of the same species

 AUTOANTIBODIES

 Abs produced against one’s own tissues WARM AND COLD ANTIBODIES

 WARM ANTIBODIES

 Abs which react best in vitro at body temperature (37C)  Usually IgG

 Require exposure to foreign Ag before they are produced, hence “acquired”

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are IgM)

 Can coat red cells at body temp and lead to removal by macrophages (extravascular hemolysis)

 Maternal IgG Abs can cross the placenta and attack fetal red cells

 COLD ANTIBODIES

 Abs which react best at 4-10C  Usually IgM

 Exist in humans regardless of whether they have been pregnant or transfused, therefore “natural”

 Most are not clinically significant, with the major exception being the ABO IgM antibodies

 When significant, IgM antibodies are very efficient at fixing complement and causes intravascular hemolysis

 Maternal IgM are NOT able to cross the placenta BLOOD GROUP SYSTEMS

1. ABO BLOOD GROUP

2. Rh BLOOD GROUP SYSTEM 3. OTHERS A. MNS B. I/i C. DUFFY D. KELL E. KIDD F. P G. LUTHERAN H. LEWIS ABO BLOOD GROUP

 First blood groups discovered

 Most significant for transfusion practice

 ABO compatibility is essential before other pretransfusion test is performed

 ABO antigens are the only antigens for which reciprocal antibodies consistently and predictably exist in serum of normal individuals

BIOCHEMISTRY:

 Paragloboside: core backbone of all of the antigens in the ABO blood group RBC] – Gl – Gal—NAG—Gal Gl: glucose Gal: Galactose NAG: N-acetylgalactosamine  H antigen:

 precursor to the A and B antigens

 made by adding a fucose (a 5-carbon sugar) to paragloboside  After (and only after) the H antigen is made, A or B antigens can

be added

 A and B antigens functionally mask the H antigen  The more A or B that is made, the less H is present

 Type O cells have no A or B and express the most H antigen  A antigen

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antigen  B antigen

 Formed by the addition of galactose to the H antigen

GROUP A

 Express A antigen on RBC surface  Genotypes AA or AO

 Have naturally occurring, clinically significant, predominantly IgM (with a small amount of IgG) antibodies against type B (anti-B)

 Subgroups

o A1 (80%) o A2 (20%)

o Significance: some with A2 have antibodies against the A1 subgroup (anti-A1)

GROUP B

 Express B Ag on RBC surface  Genotypes BB or BO

 Have naturally occurring clinically significant, predominantly IgM (with a small amount of IgG) antibodies against type A cells

GROUP O

 Have neither A nor B antigens on their RBC  Genotype OO (“universal donors”)

 Have naturally occurring, clinically significant, very high titer, anti-A, anti-B and anti-A,B antibodies

 Maternal anti-A,B can cross the placenta to cause hemolytic disease of the newborn

 Group O cells have the most H antigen GROUP AB

 Express A and B Ag on RBC surface  Genotypes A1B or A2B

 have no ABO antibodies (“universal recipients”)

Blood Group RBC Antigen Serum Ab

A A Anti-B B B Anti-A AB A & B None O none Anti-A Anti-B Anti-A,B Blood Group/ Phenotype Genotype A A1O / A1 A1 / A1 A2 A2O / A2A 2 B BB / BO AB A1B / A2B O OO

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ABO BLOOD GROUP TESTING

Forward Grouping / Forward Typing  Also called “cell” typing

 Testing for antigens on red cells

 Utilizes commercial sera containing known antibodies (A and anti-B) versus patient’s red cells

Reverse grouping /typing

 Also called “serum” or “back” typing

 Uses patient’s serum versus commercial A1 and B cells

 Analyzes patient’s serum for the presence of anti-A and anti-B antibodies

Forward Typing Reverse Typing Blood Group

Anti-A Anti-B A1 cells B cells

(+) (--) (--) (+) A (--) (+) (+) (--) B (+) (+) (--) (--) AB (--) (--) (+) (+) O (+) = Agglutination (--) = No agglutination

Common Causes of ABO Discrepancies 1. Abnormal Antigens

 Person has A2 blood group with an anti-A1 formation Forward Typing Reverse Typing

(+) (--) (+) (+)

 “Acquired B phenotype”

Seen in group A patients with exposure to gram-negative bacteria by way of intestinal obstruction, gram-negative sepsis or colon cancer

Forward Typing Reverse Typing

(++) (+) (--) (+)

2. Abnormal Antibodies or lack of appropriate antibodies  Weak or missing antibodies : newborn, elderly,

immunosuppression and other conditions that yield hypo / agammaglobulinemia

(+) (--) (--) (--)

 Non- ABO antibodies (eg polyagglutinins, multiple myeloma) present that cause agglutination of test red cells

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 BOMBAY (Oh)PHENOTYPE

 Patients lack the H gene and therefore cannot make H antigen, A or B antigen on their red cells

 Forward typing: “O”

 Discrepancies on reverse typing:

Serum agglutinates A1, B, and O cells

Confirmatory testing is done by using an anti-H reagent made from Ulex europaeus plant

(red cells + anti-H = NO agglutination)

 Have very strong anti-A, anti-B, and anti-H and can only receive cells from a Bombay donor

Rh BLOOD GROUP

 Complex blood group with >50 described antigens  Nomenclature systems  Fisher-Race (English)  antigens: D, C, E, c and e  Wiener (American)  antigens: Rho, rh’, rh”, hr’, hr”  Antigens

 Lack corresponding naturally occurring Abs (when present they are the result of sensitization caused by receipt of D-positive RBCs from another person

Fisher-Race Wiener D Rho C rh’ E rh” c hr’ e hr”  Antibodies

 Individuals who lack the antigen may be exposed to it through transfusion or pregnancy

 Anti-D (Rho), anti-C (rh’), anti-E(rh”), anti-c(hr’) and anti-e(hr”)

have all been known to cause hemolytic transfusion reaction and hemolytic disease of the newborn

 Warm-reacting, exposure-requiring IgG antibodies that are clinically significant

 Infants < 4 months usually do not form new antibodies against any incompatible red cell antigens

Rh BLOOD GROUP TESTING

 Testing for D(Rho) is the most common Rh test performed  Rh-positive simply means D-positive

 D antigens are potent immunogens.

 Of D-negative patients, 80% will develop an anti-D when transfused with a single unit of D-positive blood.

 WEAK D PHENOTYPE (Du₎

 Weakly expressed D antigens that require more sensitive testing to detect

 Quantitative difference in D antigen

 Reduced # of D antigen expressed on red cells

 All apparently D-negative blood donors must have a weak-D test to avoid false classification

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 PARTIAL D / D MOSAIC / D VARIANT PHENOTYPE  Qualitative difference in D antigen

 Number of D antigen on the red cell is not reduced but protein structure is altered

 If alloimmunized, may produce anti-D antibodies  If donating blood should be labeled as D-positive

 if receiving blood, they should be labeled as D-negative and receive D-negative units.

TRANSFUSION-RELATED TESTING

 Identify clinically significant antigens on red cells  Identify plasma antibodies to red cells

 Detect antibodies and complement bound to red cells

 IgM and IgG antibodies comprise 80% of the circulating Abs and are the most significant Abs for transfusion-related testing  To detect Ab (particularly IgG) or complement bound to RBC,

anti-human globulin reagent (Coomb’s reagent) can be added  Agglutination (clumping) of RBCs is the end result of testing –

indicating a positive reaction

COMMON TESTS USED IN IMMUNOHEMATOLOGY I. ANTIGLOBULIN (COOMB’S) TEST

 Remains the most important single test in Ab detection  Principle:

 Red blood cells sensitized by IgG or complement can be made to agglutinate by adding antihuman globulin

 DIRECT COOMB’S TEST (DAT)

 Detects RBCs that have already been sensitized with IgG

 Demonstrates that in vivo coating of RBC by Ab has occurred but does NOT identify the antibody

 INDIRECT COOMB’S TEST (IAT)

 Detects antibodies to RBC antigens present in the patient’s serum

 Detects in vitro red cell sensitization if red cells contain antigen corresponding to serum antibody

 Procedure:

STEP 1:

patient’s serum (with unknown Ab) + RBC (with known Ag)

STEP 2: product of step 1 + Coomb’s reagent

Direct Antiglobulin Test Indirect Antiglobulin Test

Patient’s red cells Patient’s serum

Detects in vivo antibody coating

(sensitization) of red cells Detects in vitro red cell sensitization if red cells contain antigen corresponding to serum antibody

Useful in:

1. Detection of hemolytic disease of the newborn (employing infant’s red cells)

2. Investigation of transfusion reactions

3. Detection of autoimmune hemolytic anemia (AIHA)

Useful in:

1. Detection and identification of unexpected antibodies

2. Compatibility testing (cross-matching)

3. Red cell antigen phenotyping 4. Investigation of transfusion

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4. Detection of red cell sensitization by drugs

(penicillin, cephalothin, alpha-methyldopa)

reactions

5. Detecting Du antigen (weak D)

II. RED CELL TYPING  Forward Typing  Reverse Typing  Rh Typing

III. CROSSMATCHING

 Absence of agglutination or hemolysis is essential to the safety of blood transfusions

 Agglutination or hemolysis in any phase of the transfusion (ie incompatibility) = presence of Ab and its corresponding Ag  Uses

 To detect antibodies in the donor or recipient  To detect ABO typing discrepancies

 Major crossmatch

 tests patient (recipient) serum + donor red cells

 Detects Abs in the patient’s serum that may destroy transfused donor RBCs

 Primarily functions to determine the ABO compatibility of the donor cells

 Minor crossmatch

 uses recipient’s red cells + donor’s serum

 Detects Abs in the donor serum which may react with Ag in the recipient

 No longer required as part of the cross match procedure

 Tested in 3 phases (major crossmatch):

 Immediate spin in saline at room temperature  Incubation at 37C with enhancement medium

 Antiglobulin phase after washing incubated cells with saline  Effects of temperature on antibodies

 IgM antibodies are usually cold antibodies and are often detected in the immediate spin phase of testing (performed at room

temperature)

 IgG antibodies usually react optimally at 37C, are referred to as warm antibodies, and are often detected in the antihuman globulin phase of testing

 Antibodies that do not react at body temp (37C) are usually not

clinically significant

IV. ANTIBODY SCREEN  Use:

 to demonstrate unexpected antibodies in the serum of the recipient that may destroy donor RBCs that were thought to be compatible on the basis of the Rh and ABO typing

 Has replaced minor crossmatching

 Procedure:

 Recipient’s serum + type O reagent red cells (with known antigens

 Will NOT detect errors in ABO typing since reagent RBCs are all group O

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V. PRE-TRANSFUSION TESTING / COMPATIBILITY TESTING 1. Review of recipient’s blood bank history

2. ABO and Rh typing of recipient & donor

3. Antibody screening of recipient & donor serum 4. Major crossmatching

HEMOLYTIC DISEASE OF THE NEWBORN

 Also referred to as erythroblastosis fetalis

 Occurs when the mother is alloimmunized to antigen(s) found on the RBC of the fetus

 Destruction of fetal RBCs by mother’s IgG antibodies HDN Due to Rh Incompatibility

 Set-up: Rh(-) mother + Rh(+) baby

 Rh (-) person exposed to Rh(+) blood will develop reaction after 2 – 4 weeks

 Mother develops antibody against the Rh(+) blood coming from the baby

 First baby is not affected; HDN occurs during subsequent pregnancies HEMOLYSIS

 May

be

prevented by giving anti-Rh to Rh(-) mother in the ante-natal (28 weeks) & immediate postnatal period (within 72 hours after delivery)  Factors which affect maternal response to Rh(+) fetal RBCs

 Concurrent ABO incompatibility  Dose of immunizing antigen  Isotype of antibody (IgM vs IgG) HDN Due to ABO Incompatibility

 Set-up: O mother + A or B baby

 ABO incompatibility occurs in 20%-25% of pregnancies  Hemolytic disease occurs only in 10%

 Treatment warranted in 1 out of 200 cases

 Not as severe as HDN due to Rh incompatibility because

 Most Anti-A & Anti-B are IgM (do not cross the placenta)  A & B antigens are poorly expressed in neonatal red cells  Many cells other than red cells express blood group A and B

antigens

ANEMIA HEMOGLOBIN

DEGRADATION

Extramedullary

hematopoiesis Hypoxic injury to the liver & heart

Increased bilirubin

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