Immunology: Secondary Response and Hypersensitivity
Overview of Immune Responses
Primary and Secondary Immune Responses
Equal numbers of T cells and B cells are required to generate a secondary immune response.
The presence of a secondary number of B cells and T cells facilitates this response.
Altering the carrier, specifically the peptide part of the hapten carrier which interacts with T cells, necessitates that T cells revert to primary mode, initiating a primary immune response despite the same hapten being present.
Key Experiments in Immunology
Thymectomy Experiment:
An important experiment conducted by Waxman, demonstrating the role of the thymus in immune response.
Radiation Experiment by Kleiman:
Radiation was used to eliminate specific cells; only fibrous and bone marrow cells were affected.
Confirmed B cells reside primarily in the bone marrow.
Following bone marrow transplant, cell populations were restored.
Role of Macrophages in Immune Response
Separation of T and B cell populations; macrophages are essential for antigen presentation.
Presentation of antigen to T cells requires macrophages; T and B cells activated upon interaction with presented antigens.
Importance of understanding how to prepare single cell suspensions of T cells, B cells, and macrophages.
Procedures must allow efficient separation of these cells.
Immune Cell Interactions
All immune cells are necessary for an anti-body response: T cells differentiate into two populations:
One helps B cells.
One helps cytotoxic cells.
Discussed the detailed pathway for T cell differentiation and how they mediate immune responses.
Cytokines and Their Roles
Cytokines play a major role in T cell activation and differentiation.
IL-2: Essential for T cell proliferation; acts in autocrine manner (T cell produces IL-2 and expresses its receptor).
Key cytokines for differentiation into T helper types (Th1 and Th2).
Focus on a limited number of key cytokines, understanding their roles in immune responses is more beneficial than memorizing all.
Mechanisms of Cytotoxic T Cells
Cytotoxic T cells are responsible for killing infected cells.
Introduction of delayed hypersensitivity reaction and its significance.
Emphasis on the necessity of a single kill, rather than multiple, in type four reactions.
Types of Hypersensitivity Reactions
Hypersensitivity Overview: Explanation of the four types of hypersensitivity reactions:
Type I (Immediate Hypersensitivity): Antibody-mediated (IgE, IgG).
Type II (Cytotoxic): Antibody-mediated, targets cells directly.
Type III (Immune Complex): Involves immune complexes causing tissue damage.
Type IV (Delayed-type): Mediated by T cells without antibodies.
Type I Hypersensitivity
Mediated by IgE antibody, featuring:
Sensitization Phase: Exposure to allergen, leading to IgE synthesis.
Activation Phase: Second exposure results in degranulation of mast cells and release of mediators.
Elicitation Phase: Effects include bronchoconstriction in lungs, dilation and leakage in blood vessels, leading to fluid build-up and allergic symptoms.
Key mediators include histamine, prostaglandins, and leukotrienes.
Type II Hypersensitivity
Characterized by cytotoxic reaction, leading to cell lysis through antibody-dependent pathways.
Examples include hemolytic anemia and reactions to Rh factor during pregnancy (Rh incompatibility) leading to damage in red blood cells of the fetus.
Type III Hypersensitivity
Dependent on immune complexes, leading to inflammation and tissue damage via the complement cascade.
Example: Serum sickness, wherein antigens (like horse serum) trigger immune complex formation that deposit in tissues.
Type IV Hypersensitivity
Delayed reaction due to T cell sensitization and activation, characterized by pro-inflammatory cytokines.
Often involves contact dermatitis and requires careful management by avoiding allergens.
Tolerance and Autoimmunity
Discussion of autoimmune diseases, associative traits and genetic predispositions.
Contrast between central tolerance (occurs in the thymus and bone marrow) and peripheral tolerance (occurs in the lymph nodes).
Central tolerance eliminates autoreactive cells through selective pressure during maturation.
Peripheral tolerance involves additional steps requiring T cell cooperation for B cell activation.
Autoimmunity Characteristics
More prevalent in females, often linked with having multiple autoimmune conditions.
Relevant concepts: Molecular mimicry and polyclonal activation can trigger autoimmunity.
Hypersensitivity reactions can also stem from external exposures triggering immune responses in predisposed individuals.
Examples of Autoimmune Diseases
Overview of common autoimmune diseases and the necessity to categorize them by type of hypersensitivity reaction (I-IV).
Need to understand each disease’s specific autoantibody and target autoantigen for comprehensive knowledge.