Immunology and Immunohematology Pt 1

Immunology and Immunohematology Overview

  • This lecture covers the interactions between immunology and immunohematology, focusing on the immune response related to blood transfusions.

  • Immunohematology (blood bank) relates to immunology as it involves the immune response to transfused cellular components: red cells, white cells, and platelets.

Immune Response Classifications

Categories of Immune Defense

  • Innate Immune Response:

    • Characteristics: Natural, non-specific response.

    • Mechanisms: Utilizes phagocytic cells to promote inflammation.

    • Components: Skin, mucosal lining, normal flora, and chemical secretions (tears and saliva).

    • Availability: Present at birth; response is rapid and unchanged by exposure.

    • Inflammation Process:

    • Vasodilation: Increase in blood flow to affected area.

    • Edema: Accumulation of fluid and neutrophils, often seen in transfusion reactions.

  • Adaptive Immune Response:

    • Characteristics: Acquired, specific response with immunological memory.

    • Mechanisms: Involves lymphocytes (B cells and T cells) that recognize specific infectious agents.

    • Function: Forms after exposure to foreign substances, specific to that stimulus.

    • Relation to blood bank: Transfusion reactions may result from antibody development.

Immune System Components

Innate vs. Adaptive Immune System

  • Innate Immunity:

    • First line of defense against pathogens.

    • Response features include rapid reaction, no prior exposure needed.

  • Adaptive Immunity:

    • Forms memory through lymphocytes.

    • Two types:

    1. Humoral Immunity:

      • Involves B lymphocytes producing antibodies; primarily IgM and later IgG.

    2. Cell-Mediated Immunity:

      • Involves T lymphocytes; includes T helper cells and T cytotoxic cells.

      • T helper cells: Stimulate humoral response, influenced by cytokine release.

      • T cytotoxic cells: Destroy affected cells, release cytokines like TNF and interferon.

Landsteiner's Law

  • Definition: Antibodies are present only when the corresponding antigen is absent from red cells.

  • This differs from broader immunology concepts.

Immune Responses in Blood Bank

Antigens and Antibodies

  • Antigens: Substances perceived as foreign that elicit an immune response; associated with specific antibodies.

    • Example: Transfusion of blood with antigen not present in recipient may trigger antibody production.

  • Antibodies: Glycoprotein molecules produced by plasma cells in response to an antigen.

    • Capable of binding specifically to that antigen; involved primarily IgM and IgG.

  • Factors Influencing Antigen-Antibody Interactions:

    • Distance on cells, ratio of antigen to antibody, pH, temperature, and immunoglobulin type.

Types of Immune Responses

Primary vs. Secondary Response

  • Primary Immune Response:

    • First exposure to antigen.

    • Characterized by low antibody titer, quick drop-off, and generation of memory cells.

  • Secondary Immune Response:

    • Subsequent exposure to same antigen (days/years later).

    • Characterized by high antibody titer, rapid response, mainly IgG.

Immunoglobulin Overview

Key Immunoglobulins in Blood Bank

  • IgG:

    • Found in highest quantity, can activate complement, crosses placenta, considered an incomplete antibody.

    • Functions in hemolytic disease of the fetus and newborn.

  • IgM:

    • First antibody produced in humoral response, best for activating complement, enhances phagocytosis.

  • IgA:

    • Found in secretions, enhances phagocytosis, prevents bacterial adherence to mucosa.

  • IgD:

    • B cell maturation; primarily found on surface of unstimulated B lymphocytes.

  • IgE:

    • Involved in allergic responses; enhances inflammation for type I hypersensitivity.

Complement System

Overview of Complement Activation

  • Definition: Plasma proteins that enhance immune response.

    • Activated directly by pathogens (innate) or indirectly by antibody-bound cells (adaptive).

  • Functions of Complement Activation:

    • Cell lysis, enhanced clearance of dead cells, initiation/amplification of inflammation.

  • Complement Activation Pathways:

    • Classical Pathway: Activated by antibody binding to antigen, leading to MAC complex formation.

    • Alternate Pathway: Does not require specific antibody; activated by microorganisms or endotoxins.

  • Complement System Components:

    • Consists of nine components (C1-C9).

Implications in Transfusion and Immune Response

  • Complement and Transfusion Reactions:

    • Activation can lead to hemolysis of transfused red cells.

    • Tests performed in blood bank (e.g., Direct Antiglobulin Test - DAP) to assess complement involvement.

  • Clinical Relevance: Understanding these concepts is crucial for anticipating transfusion reactions and managing blood bank procedures effectively.