This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Delayed-Type (Type IV) Hypersensitivity (DTH)”.
1. Type IV hypersensitivity reactions are mediated by which molecule?
a) IgG isotype
b) IgM isotype
c) T cells
d) B cells
View Answer
Explanation: Type IV hypersensitivity reactions are mediated by subpopulation of T cells i.e. CD4 Th1 cells. They encounter certain type of antigens and produce cytokines which results in induction of inflammatory reactions. These inflammatory reactions are localised and are mediated by specific inflammatory cells like macrophages.
2. Which of the following is not an example of Type IV hypersensitivity reaction?
a) Granuloma formation
b) Allergic contact dermatitis
c) Type 1 diabetes
d) Arthus reaction
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Explanation: Arthus reaction is local immune response caused due to Type III hypersensitivity reaction. This is mediated by formation and deposition of antigen-antibody complexes. On the other hand, Granuloma formation, allergic contact dermatitis and type 1 diabetes is caused by Type IV hypersensitivity reactions. These disorders are mediated by T cells as they produce cytokines for destruction of targeted macrophages.
3. Which cytokine is produced and released in order to activate macrophages?
a) IL-1
b) IL-2
c) IL-3
d) IL-5
View Answer
Explanation: IL-2 is released in order to activate macrophages. IL-2 further releases Th1 cytokines which mediate immune response and hence, accelerate the activation of macrophages and other non-specific inflammatory cells. IL-2 stimulates the growth of T cells through IL-2 receptors which in turn mediated Type IV hypersensitivity reactions. IL-2 also promotes CD4 and CD8 T cell proliferation and differentiation into effector T cells and memory T cells which mediate immune responses.
4. Which of the following is referred to as Type IV Hypersensitivity reaction?
a) Immediate hypersensitivity
b) Cytotoxic reaction
c) Immune complex reaction
d) Cell mediated hypersensitivity
View Answer
Explanation: Type IV Hypersensitivity reaction is referred to as cell-mediated hypersensitivity. This itself suggests that this hypersensitivity reaction is mediated by specific T cells. Type IV Hypersensitivity reaction is also often called as delayed type hypersensitivity and is denoted as DTH. The only differential factor between type IV and type I, II, III is that type IV is cell mediated while the latter, i.e., type I, II, III are antibody mediated. Type IV Hypersensitivity reaction involves interactions of T cells along with monocytes and macrophages.
5. The first type IV subcategory of hypersensitivity reaction, i.e., delayed type hypersensitivity, is mediated by which type of T cells?
a) CD4 Th2 cells
b) CD4 Th1 cells
c) CD8 T cells
d) Memory T cells
View Answer
Explanation: CD4 Th1 mediated reactions are termed as delayed type hypersensitivity and hence designated as first type IV subcategory of hypersensitivity reaction. This type of reaction involves introduction of antigen into the skin, Phagocytosis takes place which is mediated by antigen presenting cells. These antigen resenting cells enhance proliferation and differentiation into memory T cells which further respond to immune system. This response forces the cells to release cytokines that activate macrophages. These activated macrophages are responsible for tissue damage.
6. Type IV Hypersensitivity reaction is accomplished by which two phases?
a) Sensitization phase and effector phase
b) Generalised phase and sensitization phase
c) Effector phase and generalised phase
d) Effector phase and localised phase
View Answer
Explanation: Type IV hypersensitivity reaction is accomplished in two phases: the initial sensitization phase and the later effector phase. In the first phase, i.e., in sensitization phase, the most important mechanism takes place which is introducing a contact with antigens. During this phase, Th cells specific to that particular antigen in target bind and produce cytokines. In the second phase, i.e., in effector phase, the binding and exposure of that particular antigen gives rise to a delayed response to activate macrophages. This delayed response is therefore named as delayed type hypersensitivity. Once the macrophages are activated, they are directed to the targeted tissue for damage mechanism.
7. The second type IV subcategory of hypersensitivity reaction results in which of the following disorder?
a) Mantoux skin test
b) Contact dermatitis
c) Asthma
d) Tissue transplantation rejection
View Answer
Explanation: The second type IV subcategory of hypersensitivity is mediated by CD4 Th2 cells. It results in chronic disorders like asthma and allergic rhinitis. This case occurs only if any soluble antigen is inhaled which further results in incorporation of eosinophil in targeted tissue. This causes production of cytokines and inflammatory mediators which eventually damage the targeted tissue.
8. Which type of antigens are involved in type IV hypersensitivity reaction?
a) Intracellular pathogens
b) Endogenous antigens
c) Intracellular pathogens and contact antigens
d) Exogenous antigens
View Answer
Explanation: Type IV hypersensitivity reaction is a type of hypersensitivity reaction which is mediated by cells – specifically T cells, macrophages and monocytes. Various antigens are involved in this reaction which can be grouped into two categories—intracellular pathogens and contact antigens. Mycobacterium tuberculosis, Herpes Simplex virus, Listeria monocytogens, etc are some of the examples of intracellular pathogens. On the other hand, Nickel salts, poison ivy, etc are examples of contact antigens. These antigens react only when contacted by antibody.
9. Contact hypersensitivity occurs due to common low quality cosmetic products and soaps.
a) True
b) False
View Answer
Explanation: Contact hypersensitivity occurs after sensitisation phase. It takes place if we have contact with chemicals like nickel formaldehyde or poison ivy which is a plant material. It also occurs due to our contact with low quality soaps and cosmetic products which usually do not contain appropriate amounts of chemicals. These small molecules enter the skin and attach to body proteins which eventually induces cell-mediated hypersensitivity particularly in skin. This can cause itching, swelling, redness which further results in necrosis of that particular portion of skin which is exposed to such cosmetic and soap products.
10. Granzyme mediated apoptosis occurs in which type IV subcategory oh hypersensitivity reaction?
a) First type IV subcategory
b) Third type IV subcategory
c) Second type IV subcategory
d) Fourth type IV subcategory
View Answer
Explanation: The third type IV subcategory is mediated by CD8 cytotoxic T lymphocytes. Hence, it also called as CTL-mediated hypersensitivity reaction. This reaction causes contact derma and tissue transplantation rejection. In this type of hypersensitivity reaction, antigens are presented by antigen presenting cells with MHC I complex to naïve CD8 T cells. As a result, naïve CD8 cells get activated and further differentiate into cytotoxic T lymphocytes (CTLs). The activation of CTLs is required for destruction mechanism. As a result, activated Th1 cells play an important role in activating these CTLs. The activated CTLs then induce granzyme mediated apoptosis in the targeted cells which present same antigen with MHC I.
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