Immunology & Blood Banking/Immunohematology

IMMUNOLOGY & BLOOD BANKING / IMMUNOHEMATOLOGY

Chapter Overview

• Chapters 16 & 17 cover the principles of immunology and blood banking, focusing on immunohematology and transfusion reactions.

TERMS

• Blood Banking:

  • Procedures for collecting, storing, processing, and distributing blood for transfusion.

• Immunology:

  • Study of the molecules, cells, organs, and systems responsible for recognizing and disposing of non-self substances, including response interactions of body components, and how the immune system can be manipulated to protect against or treat diseases.

• Immunohematology:

  • Study of antigen-antibody reactions affecting blood, which includes blood transfusion medicine and blood banking.

• Transfusion Reaction:

  • Reaction of the body to a transfusion of incompatible blood; reactions range from mild fever and hives to severe conditions like renal failure, shock, and death.

IMMUNOLOGY

Antigens & Antibodies

• Antigen:

  • A foreign substance that causes an immune response, specifically the production of antibodies when introduced into a “host.”

• Antibody:

  • An immunoglobulin (protein) produced in response to a foreign antigen. This antibody binds to the antigen and initiates processes that destroy the foreign invader.

Immune Response to Pathogens

• Upon exposure to disease-causing agents (e.g., bacteria, viruses), these agents have antigens foreign to the host.

• The host produces antibodies against these antigens, attacking the pathogens and allowing the host to recover and become immune to that disease.

• Antibodies for the specific disease can remain in the body for a lifetime.

IMMUNOHEMATOLOGY

RBC Antigens & Antibodies

• Red Blood Cells (RBCs) possess hundreds of antigens on their surface.

• When someone receives blood from another person, the incoming RBCs may have antigens that are recognized as foreign by the recipient's immune system.

• If the recipient has antibodies against these foreign antigens, a transfusion reaction may occur, which can be fatal.

• Concept of Antibodies:

  • The immune system creates antibodies against antigens that it does not recognize (i.e., antigens that are foreign).

Mechanisms of Blood Exposure

• There are two main ways a person is exposed to foreign blood:

  1. Transfusion: The recipient receives donor blood.

  2. Pregnancy: A mother can be exposed to fetal blood during delivery.

• The two most important antigen groups on human RBCs are the ABO system and the Rh factor.

  • Blood typing is determined by the presence of antigen A, B, both, or neither on the surface of RBCs.

ABO Blood Group System

• ABO blood groups include:

  • Type A:

  • Antigen: A

  • Antibody in plasma: Anti-B

  • Type B:

  • Antigen: B

  • Antibody in plasma: Anti-A

  • Type AB:

  • Antigen: A and B

  • Antibody in plasma: None

  • Type O:

  • Antigen: Neither A nor B

  • Antibodies in plasma: Anti-A and Anti-B

Characteristics of Blood Groups

• Type A: RBCs with type A surface antigens; plasma contains anti-B antibodies.

• Type B: RBCs with type B surface antigens; plasma contains anti-A antibodies.

• Type AB: RBCs bear both types of surface antigens; plasma has neither anti-A nor anti-B antibodies.

• Type O: RBCs without A or B surface antigens; plasma contains both anti-A and anti-B antibodies.

Origin of ABO Antibodies

• ABO antibodies come from normal bacteria residing in the colon, which have antigens similar to A & B.

• The immune system develops antibodies against ABO antigens not present in our RBCs, typically by the age of one year.

• Individuals are born with their specific ABO antigens (blood type) inherited from parental genotypes.

Blood Transfusion Compatibility

• When matching blood for transfusion, it is crucial to ensure the recipient does not have antibodies against the donor's antigens.

  • For instance, a Type O recipient produces antibodies against A & B; receiving A or B type blood could lead to a fatal transfusion reaction known as acute hemolytic transfusion reaction.

• Universal Donor: Type O (no A or B antigens).

• Universal Recipient: Type AB (no anti-A or anti-B antibodies).

Rh System Overview

• The Rh system is the second most critical blood group system.

  • Rh antigen: D antigen.

  • Rh positive: Presence of the D antigen on RBCs.

  • Rh negative: Absence of the D antigen on RBCs.

• Exposure to Rh positive blood in Rh negative individuals results in the production of anti-D antibodies, creating a possible incompatibility in future transfusions or pregnancies.

Rh Incompatibility in Maternal-Fetal Context

• 1st Pregnancy: Rh negative mother and Rh positive father can produce an Rh positive infant.

  • The mother gets exposed to the baby's D antigen during delivery, generating anti-D antibodies.

• 2nd Pregnancy: If the mother becomes pregnant again with another Rh positive baby, her anti-D antibodies can cross the placenta and attack the baby's Rh positive RBCs, resulting in hemolytic disease of the fetus and newborn (HDFN).

  • HDFN can be fatal.

Prevention of HDFN

• To prevent HDFN, all Rh negative pregnant women must receive the RhIG (RhoGam) shot at around 7 months of gestation and again after delivery if the baby is Rh positive.

  • RhIG contains anti-D antibodies that bind to the Rh positive cells in the mother’s circulation, removing them before the mother's immune system recognizes them as foreign and begins producing her own anti-D.

BLOOD TYPING

Methods of Blood Typing

• The antigen type on RBCs is determined by testing them against known antibodies.

  • Clumping/agglutination indicates a positive result (the presence of that specific antigen).

  • Results are recorded for both ABO typing and Rh typing.

Forward vs. Reverse Typing

• Forward Typing: Identifies antigens on patient cells using manufactured reagent antibodies.

• Reverse Typing: Detects antibodies in patient plasma using manufactured reagent RBCs (specifically A and B types).

• An ABO Discrepancy occurs when forward typing results do not match reverse typing results using the same patient plasma.

Indications for Blood Transfusion

• Circumstances when a transfusion may be needed include:

  • Surgery

  • Serious injuries

  • Severe infections

  • Liver disease affecting blood production

  • Anemia from different diseases (cancer, bleeding disorders, medication effects)

PRETRANSFUSION COMPATIBILITY TESTING

Components of Compatibility Testing

• Critical steps in pretransfusion compatibility testing entail:

  • Proper identification of the intended recipient (most crucial step).

  • Assessment of the ABO and Rh type for both recipient and donor unit (double-checking labels).

  • Antibody screening for unexpected antibodies in the recipient's plasma.

  • Crossmatch test to ensure that recipient plasma doesn't contain antibodies against donor RBCs.

• Autologous transfusion: Procedure where an individual donates blood for their future use, primarily beneficial for those with antibodies against antigens found on most RBCs.

OTHER BLOOD COMPONENTS

Overview of Blood Blood Components

• Blood can be categorized into several components:

  • Whole Blood:

  • Can be divided into RBCs, platelets, and fresh frozen plasma (FFP).

  • Packed Red Cells:

  • Contains no viable platelets or neutrophils.

  • Platelets:

  • Important for coagulation, containing plasma with coagulation factors, some red cells, and some white cells (leukocytes).

  • Fresh Frozen Plasma (FFP):

  • Contains all coagulation factors in normal amounts, free from red cells, leukocytes, and platelets.

Indications for Blood Component Usage

• Packed Red Cells: For use in cases of substantial hemorrhage and symptomatic anemia.

• Platelets: For patients with bleeding due to thrombocytopenia or platelet dysfunction, and to manage temporary thrombocytopenia following chemotherapy.

• Fresh Frozen Plasma (FFP): Utilized for correction of known coagulation factor deficiencies or treatment of microvascular hemorrhage in individuals with prolonged PT/aPTT.