Immunohematology Made Easy: Quick Tips & Bullet Points (Ongoing)

This series is designed to simplify the world of immunohematology by breaking down key concepts into easy-to-understand tips, notes, and bullet points. Whether you’re a student, professional, or enthusiast, each entry will provide quick, digestible insights on essential topics like blood group systems, transfusion safety, and immunological principles. Perfect for on-the-go learning or a quick refresher, this resource will help you master immunohematology in no time.

Basic Immunology and Immunohematology Principles:

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Immunohematology is the study of blood group antigens and antibodies, focusing on immune responses related to blood transfusions.

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Basic Immunology and Immunohematology Principles:

Transfused blood components (red cells, leukocytes, platelets) can trigger immune responses in the recipient.

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Basic Immunology and Immunohematology Principles:

Understanding basic immunology is crucial for transfusion medicine.

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Basic Immunology and Immunohematology Principles:

Antigen: A molecule that binds to an antibody or T-cell receptor, either in the body (in vivo) or in a laboratory (in vitro).

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Basic Immunology and Immunohematology Principles:

Antigens are typically large molecules, primarily proteins (including glycoproteins, lipoproteins, nucleoproteins) and polysaccharides (including lipopolysaccharides).

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Basic Immunology and Immunohematology Principles:

Antigens are found on cell membranes, viruses, bacteria, fungi, protozoa, blood cells, organs, and tissues.

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Basic Immunology and Immunohematology Principles:

Hapten: A small molecule that is not immunogenic on its own.

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Basic Immunology and Immunohematology Principles:

Hapten requires binding to a carrier molecule (usually a protein) to become immunogenic and initiate an immune response.

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Basic Immunology and Immunohematology Principles:

Once part of a hapten-carrier complex, it can stimulate antibody production and react with these antibodies.

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Basic Immunology and Immunohematology Principles:

Examples of haptens include medications like penicillin, which can cause anaphylaxis by forming complexes with body proteins.

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Basic Immunology and Immunohematology Principles:

Hapten Reactivity: Haptens can react specifically with the antibodies produced against the complex (hapten-carrier complex), leading to immune or allergic reactions.

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Basic Immunology and Immunohematology Principles:

Immunogens vs. Antigens: Key Difference

Immunogen Definition: An antigen that elicits or stimulates an immune response.

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Basic Immunology and Immunohematology Principles:

Immunogens vs. Antigens: Key Difference

Antigen (Broader Term): Any foreign molecule that can bind to immune system components (antibodies, T-cell receptors).

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Basic Immunology and Immunohematology Principles:

Immunogens vs. Antigens: Key Difference

Relationship: All immunogens are antigens, but not all antigens are immunogens. Immunogens are antigens capable of triggering an immune response.

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Basic Immunology and Immunohematology Principles:

Immunogens vs. Antigens: Key Difference

Immunogenicity Factors: The ability to trigger an immune response varies based on the molecule’s characteristics and the individual’s immune system.

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Basic Immunology and Immunohematology Principles:

Immunogens vs. Antigens: Key Difference

Immunogenicity : Proteins are generally the most immunogenic, followed by carbohydrates, and then lipids (which are less immunogenic). Complex molecules are more immunogenic than simple ones.

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Basic Immunology and Immunohematology Principles:

Allogeneic vs. Autologous Antigens: Self vs. Non-Self

Allogeneic Antigens:
- Antigens originating from a genetically different individual of the same species.

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Basic Immunology and Immunohematology Principles:

Allogeneic vs. Autologous Antigens: Self vs. Non-Self

Allogeneic Antigens:

In transfusion, these are foreign antigens on donor blood cells that can be recognized by the recipient’s immune system.

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Basic Immunology and Immunohematology Principles:

Allogeneic vs. Autologous Antigens: Self vs. Non-Self

Autologous Antigens:

“Self-antigens” originating from the individual’s own body.

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Basic Immunology and Immunohematology Principles:

Allogeneic vs. Autologous Antigens: Self vs. Non-Self

Autologous Antigens:

Normally, the immune system is tolerant to autologous antigens.

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Basic Immunology and Immunohematology Principles:

Allogeneic vs. Autologous Antigens: Self vs. Non-Self

Autologous Antigens:

Failure of self-tolerance can lead to autoimmune diseases.

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Basic Immunology and Immunohematology Principles:

Allogeneic vs. Autologous Antigens: Self vs. Non-Self

Transfusion Context:
- Allogeneic transfusion: Recipient is exposed to antigens different from their own.
- Autologous transfusion: Uses the recipient’s own blood, so antigens are “self”.

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

Humoral Response in Transfusion: In blood transfusions, the primary immune response to foreign red cell antigens is humoral, mainly involving B lymphocytes (B cells).

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

B Cell Recognition and Activation:
- Recipient’s B cells recognize foreign red cell antigens through their B-cell receptors.
- This recognition triggers B cells to present the antigen to T lymphocytes (T cells).

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

T Cell Involvement and Cytokine Signaling:
- T cells, after antigen presentation by B cells, release cytokines.
- Cytokines act as signals that stimulate B cells to transform into plasma cells.

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

Plasma Cell Function: Antibody Production:

Plasma cells are differentiated B cells that function as antibody factories.
Each plasma cell is a clone, producing antibodies with a single, specific target (same specificity as the original B-cell receptor).

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

Plasma Cell Function: Antibody Production:

Antibodies are glycoprotein molecules that circulate in the blood.
Antibodies specifically recognize and bind to the foreign antigen that initiated the immune response.

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

Memory B Cells: Long-Term Immunity:

Alongside plasma cells, memory B cells are also produced during the initial immune response.

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

Memory B Cells: Long-Term Immunity:

Memory B cells persist in circulation, providing immunological memory.
Upon subsequent exposure to the same antigen, memory B cells rapidly activate and differentiate into plasma cells, leading to a faster and stronger antibody response.

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Basic Immunology and Immunohematology Principles:

Immune Response to Antigens

Memory B Cells: Long-Term Immunity:

Memory B cell activation in secondary responses does not require T cell presentation, allowing for a quicker reaction.
This principle of memory B cells is fundamental to the effectiveness of vaccination.

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Basic Immunology and Immunohematology Principles:

Antigenic Determinants (Epitopes): Targets of Antibodies:

Transfused red cells have multiple antigens on their surfaces.

Each antigen possesses multiple antigenic determinants, also known as epitopes.

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Basic Immunology and Immunohematology Principles:

Antigenic Determinants (Epitopes): Targets of Antibodies:

Epitopes are specific sites on an antigen that can stimulate the immune response and are recognized by antibodies.

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Basic Immunology and Immunohematology Principles:

Antigenic Determinants (Epitopes): Targets of Antibodies:

B cells have unique receptors that can interact with specific epitopes.

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Basic Immunology and Immunohematology Principles:

Antigenic Determinants (Epitopes): Targets of Antibodies:

Antibodies produced during an immune response are directed against and bind to specific epitopes on an antigen.

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Basic Immunology and Immunohematology Principles:

Antigenic Determinants (Epitopes): Targets of Antibodies:

The immune response to a single antigen can involve the production of multiple different antibodies, each targeting a distinct epitope on that antigen.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Antibodies are glycoproteins belonging to the immunoglobulin (Ig) protein family.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Terms “antibody” and “immunoglobulin” are often used interchangeably.
Two main functions:
- Bind to specific antigens (epitopes).
- Mediate various biological effects to clear the antigen.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Molecular Structure:

Composed of four polypeptide chains:
- Two identical heavy chains.
- Two identical light chains.

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Antibodies & Immunoglobulins (Ig):

Molecular Structure:

Chains are linked by disulfide bonds (S-S bridges).
Disulfide bonds provide flexibility in the antibody’s 3D shape.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Five Antibody Classes (Isotypes):

Five classes based on heavy chain differences: IgG, IgA, IgM, IgD, IgE.
Each class has unique physical, chemical, and biological properties.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Heavy Chains Determine Isotype: Distinctive heavy chains (e.g., alpha for IgA) give each class specific functions.
- IgA: Found in mucosal linings.
- IgE: Activates mast cells, involved in immediate hypersensitivity.
- IgD: Antigen receptor on naive B cells.
- IgM & IgG: Most relevant in transfusion medicine.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Light Chains:
- Two types: kappa and lambda chains.
- Each antibody has either two kappa or two lambda chains, never one of each.

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Antibodies & Immunoglobulins (Ig):

Variable Regions:

Located at the amino-terminal ends of both heavy and light chains.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Variable Regions:

Responsible for antigen binding specificity.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Variable Regions:
- Form the idiotope – the antigen-binding site or pocket.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Constant Regions:

Non-variable portions of heavy and light chains.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Constant Regions:
- Constant region of the heavy chain determines antibody class function (e.g., complement activation, cell attachment).

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Hinge Region:

Part of the heavy chains between Fab and Fc regions.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Hinge Region:

Provides flexibility to the antibody molecule.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Hinge Region:
- Allows the two antigen-binding sites to operate independently.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fab and Fc Regions (Fragments):

Generated by enzyme cleavage (papain, pepsin) to study antibody structure.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fab (Fragment antigen binding):

Contains the variable regions and parts of the constant regions of both heavy and light chains.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fab (Fragment antigen binding):
- Responsible for antigen binding.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fc (Fragment crystallizable):

Composed of the remaining constant domains of the two heavy chains.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fc (Fragment crystallizable):

Mediates biological effector functions.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fc (Fragment crystallizable):

Fc receptors exist on immune cells like macrophages and neutrophils.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Fc (Fragment crystallizable):

Fc region binding to these receptors facilitates phagocytosis of antibody-coated cells or pathogens.

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Basic Immunology and Immunohematology Principles:

Antibodies & Immunoglobulins (Ig):

Antibodies in Transfusion Medicine and Extravascular Hemolysis:
- Antibodies attached to red cell antigens (especially IgG) can signal their removal.
- Fc region interaction with phagocytes in the liver and spleen leads to red cell destruction.
- This process is called extravascular hemolysis.

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