lecture-32-immune hypersensitivity- kaushik

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Questions and Answers

What is the role of IgM antibodies in transfusion reactions compared to IgG antibodies?

IgM antibodies do not participate in hemolytic reactions.

IgM antibodies solely target viral infections.

IgM antibodies are less effective at complement activation.

IgM antibodies are more effective at complement activation. (correct)

Which symptom is commonly associated with hemolytic disease of the newborn?

Excessive leukocyte production

Severe jaundice (correct)

Increased platelet count

High hemoglobin levels

What is the purpose of administering Rhogam during pregnancy?

To enhance fetal blood count.

To increase maternal IgG production.

To prevent hemolytic disease in a subsequent pregnancy. (correct)

To stimulate fetal growth.

What can trigger drug-induced hemolytic anemia?

Adverse reactions to non-specific adsorbed drugs on RBC membranes. Signup and view all the answers

In thrombocytopenia, what is a prominent clinical feature observed?

Purpura, areas of purplish discoloration. Signup and view all the answers

What are isohemagglutinins?

Antibodies produced in response to non-self blood group antigens Signup and view all the answers

What primarily causes immediate hemolytic transfusion reactions?

ABO blood-group incompatibilities Signup and view all the answers

What are the symptoms of immediate hemolytic transfusion reactions?

Hemoglobinuria, fever, and chills Signup and view all the answers

Delayed hemolytic transfusion reactions are typically caused by which type of antibodies?

IgG antibodies Signup and view all the answers

How long after a transfusion do delayed hemolytic transfusion reactions usually develop?

2-6 days Signup and view all the answers

What is a primary treatment for immediate hemolytic transfusion reactions?

Prompt termination of the transfusion Signup and view all the answers

What role does H antigen play with ABO/ABH blood-group antigens?

It is present in all blood types Signup and view all the answers

Which mechanism is involved in the destruction of transfused RBCs during a transfusion reaction?

Complement-mediated lysis Signup and view all the answers

Which of the following conditions is a potential cause of drug-induced hemolytic anemia?

Autoimmune response to medications Signup and view all the answers

To prevent erythroblastosis fetalis, which intervention is critical?

Administering Rh immunoglobulin to Rh-negative mothers Signup and view all the answers

What antibody is primarily responsible for mediating immediate hemolytic transfusion reactions?

IgM Signup and view all the answers

Which blood group antigen is present in all blood types?

H antigen Signup and view all the answers

What is a common clinical manifestation associated with immediate hemolytic transfusion reactions?

Hemoglobinemia Signup and view all the answers

Delayed hemolytic transfusion reactions are primarily associated with which class of antibodies?

IgG Signup and view all the answers

Which of the following treatments is critical for managing immediate hemolytic transfusion reactions?

Termination of transfusion and diuretic administration Signup and view all the answers

What is the primary cause of Goodpasture's syndrome?

Autoantibodies against collagen proteins Signup and view all the answers

Which statement best describes pemphigus?

It leads to the formation of blisters due to autoantibodies against desmogleins. Signup and view all the answers

What triggers type II hypersensitivity in organ transplantation?

Pre-existing alloantibodies against MHC molecules Signup and view all the answers

In type III hypersensitivity, what is the primary consequence of immune complex deposition?

Recruitment of neutrophils and tissue damage Signup and view all the answers

What standard treatment is typically administered for pemphigus?

Corticosteroids Signup and view all the answers

What primarily causes mild to severe anemia in the fetus during erythroblastosis fetalis?

Destruction of fetal blood cells by maternal antibodies Signup and view all the answers

Which of the following is a common result of IgG-mediated transfusion reactions?

Extravascular destruction of RBCs Signup and view all the answers

How can the risk of thrombocytopenia be increased through hypersensitivity reactions?

By contributing to increased platelet destruction via anti-platelet antibodies Signup and view all the answers

What clinical manifestation characterizes the condition of thrombocytopenia?

Purplish discoloration of the skin known as purpura Signup and view all the answers

Which condition is most likely to occur if maternal IgG antibodies target fetal blood group antigens?

Hemolytic disease of the newborn Signup and view all the answers

What primarily distinguishes autoimmune hemolytic anemia from hemolytic anemia caused by alloantibodies?

Autoimmune hemolytic anemia involves antibodies directed against one's own red blood cells. Signup and view all the answers

Which mechanism does not contribute to the destruction of cells in type II hypersensitivity?

Direct lysis by IgE antibodies. Signup and view all the answers

What is a characteristic feature of cold autoantibodies in autoimmune hemolytic anemia?

They may trigger episodes of acute hemolysis during colder months. Signup and view all the answers

Which of the following is an example of a reaction that can induce type II hypersensitivity?

Blood transfusion reactions. Signup and view all the answers

What is the most common response of the body during type II hypersensitivity when autoantibodies are produced?

Direct binding of antibodies to self-antigens leading to cell lysis. Signup and view all the answers

What is a significant outcome of the conversion of hemoglobin to bilirubin in cases of erythroblastosis fetalis?

Brain damage due to bilirubin deposition Signup and view all the answers

In drug-induced hemolytic anemia, how do certain drugs contribute to the production of antibodies against RBCs?

By adsorbing non-specifically to RBC membrane proteins Signup and view all the answers

What is the primary mechanism that leads to thrombocytopenia mediated by type II hypersensitivity?

Destruction of platelets by antiplatelet antibodies Signup and view all the answers

Which of the following conditions can lead to severe consequences in newborns due to maternal IgG antibody transfer?

Hemolytic disease of the newborn Signup and view all the answers

What prompts the administration of Rhogam to Rh-negative mothers during pregnancy?

To inhibit the formation of maternal IgG antibodies against fetal Rh+ cells Signup and view all the answers

What is the primary cause of a transfusion reaction when a type ‘A’ individual receives type ‘B’ blood?

Binding of anti-B isohemagglutinins to B blood cells Signup and view all the answers

Which statement describes the characteristic of isohemagglutinins in adults?

They are predominantly of IgM isotype for antigens not expressed Signup and view all the answers

What is a potential complication of hemoglobin accumulation in the kidneys post-transfusion?

Tubular necrosis due to toxicity Signup and view all the answers

How does the presence of the H antigen influence blood transfusions?

It serves as the only blood group antigen recognized in all individuals Signup and view all the answers

What is the role of natural exposure to microbial antigens in blood type antibody production?

It stimulates antibody production specific to non-self blood group antigens Signup and view all the answers

Study Notes

Type II Hypersensitivity

Clinical damage occurs when antibodies (Abs) bind directly to antigens (Ags) on cell surfaces, leading to cell lysis.
Involves antibody-mediated destruction of cells, mainly by IgM or IgG, not IgE.
Antibodies can attack mobile cells (leukocytes/RBCs) or fixed cells in tissues.
Antigens recognized can be foreign substances or autoantigens bound to the cell surface.
Pathological antibodies (autoantibodies) circulate freely in the periphery, binding to self-antigens, potentially causing autoimmune diseases.

Examples of Type II Hypersensitivity

Blood transfusions reactions
Hemolytic disease of the newborn (Rh disease)
Anemias (some forms)
Drug reactions (drug-induced hemolytic anemia)
Platelet disorders
Tissue transplant reactions
Autoimmune disorders (not detailed)

Mechanisms of Type II Hypersensitivity

Complement activation: Antibodies trigger complement activation, creating pores in the cell membrane, leading to cell lysis.
Antibody-dependent cell-mediated cytotoxicity (ADCC): Antibodies bind to foreign cells, marking them for destruction by immune cells (e.g., natural killer cells).
Antibody opsonization: Antibodies coat foreign cells, facilitating their phagocytosis by phagocytic cells. Complement proteins (e.g., C3b) may be involved.

Hemolytic Anemias

Hemolytic anemia involves the destruction of red blood cells (RBCs).
Destruction can occur in blood vessels, spleen, or liver.
Autoantibodies or alloantibodies can cause this destruction.

Autoimmune Hemolytic Anemias

Autoantibodies target the individual's own RBCs.
Antibodies can be warm (37°C) or cold (below 37°C), depending on optimal activity temperature.
Warm antibody-mediated hemolytic anemia is acute onset and often treated with glucocorticoids.
Cold antibody-mediated hemolytic anemia episodes might be triggered by cold weather.

Alloimmune Hemolytic Anemias/Blood Transfusion Reactions

Individuals can mount an antibody response to different allelic forms of blood group antigens in transfused blood (foreign antigens).
Blood type antigens (ABH) are predominantly carbohydrates, not primarily proteins.
Exposure to common gut flora can trigger antibodies against blood group antigens.

Thrombocytopenias (Type II HS)

Thrombocytopenia involves abnormally low platelet counts, leading to impaired blood clotting.
Causes include decreased platelet production, increased destruction, and abnormal distribution of platelets in the body.
Anti-platelet antibodies contribute to immune system-mediated thrombocytopenia, increasing the destruction of platelets.

Other Examples of Type II HS

Ab-mediated rejection in solid tissue transplants: Pre-existing antibodies against donor MHC molecules can cause immediate rejection.
Goodpasture's syndrome: Autoantibodies target collagen in glomeruli in the kidney and alveoli in the lungs.
Pemphigus: Autoantibodies attack cell adhesion proteins (desmogleins).

Immune Complex-Mediated Type III Hypersensitivity

Immune complexes (Ag-Ab) are typically cleared by phagocytic cells.
In some cases, complexes deposit in tissues, leading to inflammation and tissue damage.
The magnitude of the reaction depends on the quantity and distribution of immune complexes in the body.
Activation of mast cells, neutrophils, and macrophages releases inflammatory mediators, increasing vascular permeability leading to tissue damage.

Type III Hypersensitivity (Localized and Generalized)

Localized reactions (e.g., Arthus reaction): Occur after injecting antigen.
Generalized reactions (e.g., serum sickness): Follow exposure to large amounts of antigen.

Type IV (Delayed-Type) Hypersensitivity (DTH)

Cell-mediated hypersensitivity rather than antibody-mediated
Tissue damage primarily caused by effector T cells (e.g., Th cells, CTLs), macrophages.
Key example: Tuberculin reaction
Delayed-onset inflammation.
DTH response phases: Sensitization & Effector
Sensitization phase: Antigen exposure to develop specific T cells
Effector phase: Antigen encounters sensitized T cells to cause inflammation

Contact Hypersensitivity (Type IV)

Secondary immune response to small, chemically reactive molecules binding to self-proteins in the skin's upper layers.
Examples: poison ivy, poison oak, hair dyes, nickel salts, latex, and certain drugs.

Other characteristics of Type IV Hypersensitivity

Detected using skin tests (e.g., tuberculin test)
Characteristic skin lesions (e.g., redness, swelling) appear after a delayed period.

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Description

This quiz covers the mechanisms, clinical damage, and examples of Type II hypersensitivity reactions. Understand how antibodies interact with antigens, leading to various medical conditions, including autoimmune diseases and transfusion reactions. Test your knowledge on this crucial topic in immunology.