Immunopathology Practice Questions

Q: Molecular mimicry is an explanation for which of the following?

Autoimmune disorders. ### Explanation **Molecular Mimicry** is a key mechanism in the pathogenesis of **Autoimmune Disorders** [1]. It occurs when there is a structural similarity between the antigens of an infectious agent (bacteria or virus) and the host’s self-antigens. When the immune system mounts a response against the pathogen, the cross-reactive antibodies or T-cells mistakenly attack the host’s own tissues, leading to loss of self-tolerance and subsequent tissue damage [1]. **Why the other options are incorrect:** * **Immune Tolerance:** This is the state of unresponsiveness to an antigen. Molecular mimicry represents a *failure* of tolerance, specifically a breakdown in peripheral tolerance. * **Hypersensitivity:** While autoimmunity involves hypersensitivity reactions (Types II, III, or IV), "Hypersensitivity" is a broad category describing exaggerated immune responses to *exogenous* antigens (like pollen or drugs). Molecular mimicry specifically explains the *trigger* for attacking *endogenous* (self) antigens [1]. * **Immunosuppression:** This refers to a reduced activation or efficacy of the immune system (e.g., HIV or chemotherapy). Molecular mimicry involves an *overactive* and misdirected immune response. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Example:** **Rheumatic Heart Disease.** Antibodies against the M-protein of *Streptococcus pyogenes* cross-react with cardiac myosin, leading to carditis. * **Guillain-Barré Syndrome (GBS):** Lipopolysaccharides of *Campylobacter jejuni* mimic gangliosides in peripheral nerves. * **Type 1 Diabetes:** Potential mimicry between Coxsackie B virus antigens and islet cell antigens (GAD65) [1]. * **Ankylosing Spondylitis:** Associated with *Klebsiella* species cross-reacting with HLA-B27. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 219-226.

Question 1

Which of the following is NOT a disorder of phagocytosis?

Accepted Answer

Wiskott-Aldrich syndrome

Answer

Job's syndrome

Answer

Chediak-Higashi syndrome

Answer

Myeloperoxidase deficiency

Question 2

Molecular mimicry is an explanation for which of the following?

Accepted Answer

Autoimmune disorders

Answer

Immune tolerance

Answer

Hypersensitivity

Answer

Immunosuppression

Question 3

Erythroblastosis fetalis is an example of which type of hypersensitivity reaction?

Accepted Answer

Type II

Answer

Type I

Answer

Type III

Answer

Type IV

Question 4

A patient on treatment with penicillin developed pallor, but without shortness of breath, urticaria, or wheezing. Investigations revealed antibodies against penicillin in his blood. What is the most likely type of hypersensitivity reaction that occurred in this patient?

Accepted Answer

Type II hypersensitivity

Answer

Type I hypersensitivity

Answer

Type III hypersensitivity

Answer

Type IV hypersensitivity

Question 5

Asthma is classified as which type of hypersensitivity reaction?

Accepted Answer

Type I hypersensitivity

Answer

Type II hypersensitivity

Answer

Type III hypersensitivity

Answer

Type IV hypersensitivity

Question 6

All are true regarding Severe Combined Immunodeficiency (SCID) except:

Accepted Answer

Toxicity of leucocytes due to accumulation of cyclic adenosine monophosphate (cAMP)

Answer

Due to deficiency of adenosine deaminase

Answer

Both cellular and humoral immunity are affected

Answer

Bone marrow transplantation is a treatment option

Question 7

MHC is important in the pathogenesis of which of the following conditions?

Accepted Answer

Auto-immune diseases

Answer

Idiopathic disease

Answer

Iatrogenic diseases

Answer

Tumours

Question 8

Which immunoglobulin is predominantly found in breast milk and other secretions?

Accepted Answer

IgA

Answer

IgE

Answer

IgG

Answer

IgD

Question 9

Anti-Ro antibody is associated with which of the following conditions?

Accepted Answer

Neonatal Lupus

Answer

Systemic Lupus Erythematosus (SLE)

Answer

Scleroderma

Answer

Mixed Connective Tissue Disease (MCTD)

Question 10

All of the following are disorders of phagocytosis except?

Accepted Answer

Nezelof Syndrome

Answer

Chronic granulomatous disease

Answer

Myeloperoxidase deficiency

Answer

Chediak-Higashi Syndrome

Immunopathology — MCQs

Immunopathology — MCQs

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