Immunology Practice Questions

Q: Which of the following is not considered an antigen-presenting cell?

Thymocytes. ***Thymocytes*** - Thymocytes are **developing T cells** found in the thymus and do not function as antigen-presenting cells (APCs) [1]. - Unlike APCs, thymocytes are primarily involved in the **maturation** and selection of T lymphocytes. *Langerhans cells* - Langerhans cells are a type of **dendritic cell** found in the skin and are effective antigen-presenting cells to T cells [1]. - They play a crucial role in **immune surveillance** and response to skin infections. *Macrophages* - Macrophages are well-known antigen-presenting cells that engulf pathogens and present antigens to T cells [1]. - They are also involved in **phagocytosis** and secrete various cytokines to modulate immune responses. *M-cells* - M-cells (microfold cells) are specialized epithelial cells that transport antigens from the intestinal lumen to underlying immune cells. - Although not traditional APCs, they play a role in immune surveillance and stimulating **mucosal immunity**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 200, 207-208.

Q: Viral infection is differentiated from bacterial infection by:

Interferon production. ***Interferon production*** - **Interferons** are cytokines primarily produced by host cells in response to **viral infections**, playing a crucial role in antiviral defense. - Interferon production is a **hallmark of viral infection** and the primary mechanism differentiating viral from bacterial pathogenesis. - While bacteria can induce some interferon responses, their primary immune evasion and pathogenesis mechanisms do **not center around interferon production** in the same way as viruses. *Toxin production* - **Bacterial toxins** (exotoxins, endotoxins) are far more common and represent a primary mechanism of bacterial pathogenicity. - Most viruses do not produce classical toxins; they damage cells primarily through direct cytopathic effects and immune-mediated mechanisms. *Neutrophilia* - An increase in **neutrophils** (neutrophilia) is a classic hallmark of acute **bacterial infections**, as neutrophils are the primary phagocytes that fight bacteria. - Viral infections typically lead to a normal or decreased neutrophil count, often accompanied by a relative increase in lymphocytes. *Lymphocytosis* - A relative **lymphocytosis** (increased lymphocyte count) is often indicative of **viral infection**, as part of the adaptive immune response. - Both viral and bacterial infections activate lymphocytes, but viral infections characteristically show predominant lymphocyte response, while bacterial infections more commonly cause **neutrophilic leukocytosis**.

Q: Adoptive immunity is by what mechanism?

Injection of lymphocytes. ***Injection of lymphocytes*** - **Adoptive immunity** refers to the transfer of immunity by transferring immune cells, specifically **lymphocytes**, from an immune individual to a non-immune individual. - This method directly provides the recipient with pre-existing, functional immune cells capable of mediating an immune response. *Natural infection* - Natural infection leads to **active immunity**, where an individual's own immune system responds to a pathogen and generates memory cells and antibodies. - This process involves the host's immune system actively recognizing and clearing the pathogen, not the transfer of pre-formed immune cells. *Passive transfer of antibodies* - This describes **passive immunity**, where pre-formed **antibodies** are transferred from one individual to another, providing immediate but temporary protection. - While it confers immunity, it does not involve the transfer of whole immune cells (lymphocytes) that can mount a sustained cellular immune response. *Vaccination with killed pathogens* - Vaccination, even with killed pathogens, induces **active immunity** by stimulating the recipient's own immune system to produce antibodies and memory cells. - This method aims to generate a primary immune response internally rather than directly providing effector immune cells.

Q: A 62-year-old woman presents with fever, cough, sputum production, and pleuritic chest pain. Chest X-ray reveals a right middle lobe infiltrate, and she is started on antibiotics for the treatment of pneumonia. Her sputum Gram stain is positive for S. pneumoniae. Which of the following immunologic mechanisms is the most specific host defense against pneumococcal infection?

IgG antibody directed against capsular antigens. ***IgG antibody directed against capsular antigens*** - **IgG antibodies** against the capsular polysaccharides of *S. pneumoniae* are crucial for **opsonization** and subsequent **phagocytosis**, providing specific and effective immunity. - This antibody response is essential for **humoral immunity** and forms the basis of pneumococcal vaccines. *complement system activity* - The **complement system** plays a role in immunity against *S. pneumoniae* by promoting **opsonization** and bacterial lysis, especially through the classical and alternative pathways. - However, while important, it is not as specific as IgG antibodies directed against the **capsular antigens** because it can be activated by various pathogens and mechanisms. *macrophage activity in the alveoli* - **Alveolar macrophages** are crucial initial responders in the lungs, phagocytosing bacteria and initiating inflammation. - While they are important in the **early innate immune response**, their effectiveness against encapsulated bacteria like *S. pneumoniae* is significantly enhanced by opsonization through antibodies and complement. *functional splenic activity* - The **spleen** is vital for clearing encapsulated bacteria, including *S. pneumoniae*, from the bloodstream, particularly in individuals with **asplenia**. - Its role is primarily in filtering blood and housing phagocytic cells, but it relies on an effective **antibody-mediated mechanism** for optimal clearance.

Q: All of the following forces are involved in antigen-antibody reactions, except:

Covalent bond. ***Covalent bond*** - **Covalent bonds** are strong, irreversible bonds that involve the sharing of electrons between atoms. - Antigen-antibody interactions are predominantly **non-covalent** and reversible, allowing for dynamic binding and release. *Vander Waal's forces* - **Van der Waals forces** are weak attractive forces that arise from temporary fluctuations in electron distribution, creating transient dipoles. - They are crucial in antigen-antibody binding, especially when the molecules are in **close proximity**, contributing to overall affinity. *Electrostatic bond* - **Electrostatic (ionic) bonds** occur between oppositely charged groups on the antigen and antibody surfaces. - These interactions are significant for **initial recognition** and overall binding stability, particularly at appropriate pH levels. *Hydrogen bond* - **Hydrogen bonds** form between a hydrogen atom covalently linked to an electronegative atom (like oxygen or nitrogen) and another electronegative atom. - They play a vital role in the **specificity and strength** of antigen-antibody interactions by providing numerous weak, directional contacts.

Q: Congenital passive immunity is INADEQUATE in -

Pertussis. ***Pertussis*** - **Congenital passive immunity** against *Bordetella pertussis* is **most inadequate** among the listed infections. - **Minimal transplacental transfer** of protective IgG antibodies occurs, and maternal antibodies decline rapidly in infants. - Newborns have **virtually no protection** from maternal antibodies, making them highly susceptible to severe whooping cough. - This is why **early vaccination at 6 weeks** is critical, unlike measles which can wait until 9-12 months. *Measles* - Maternal antibodies provide **excellent passive immunity** protecting infants for **6-9 months**. - This robust protection is why measles vaccination is delayed until 9-12 months of age. - Represents the **gold standard** of effective maternal antibody transfer. *Mumps* - Maternal antibodies provide **good passive immunity** in early infancy. - Mumps in young infants is rare due to this maternal protection. *RSV (Respiratory Syncytial Virus)* - Maternal antibodies provide **limited but present** passive immunity. - Unlike pertussis where protection is nearly absent, RSV maternal antibodies can **reduce severity** of illness. - However, RSV remains a major cause of bronchiolitis in infants despite this partial protection. - The key difference: RSV has **some** maternal protection (inadequate but present), whereas pertussis has **almost none** (most inadequate).

Q: Which type of antibody is primarily involved in the secondary immune response?

IgG. ***IgG*** - **Immunoglobulin G (IgG)** is the predominant antibody in the **secondary immune response**, offering long-term immunity and protection. - It is produced in large quantities and has a longer half-life compared to other immunoglobulins, allowing for sustained defense against pathogens. *IgA* - **Immunoglobulin A (IgA)** is primarily found in **mucosal secretions** like tears, saliva, and breast milk, providing local immunity. - While important for first-line defense, it is not the main antibody elevated during a secondary systemic immune response. *IgM* - **Immunoglobulin M (IgM)** is the first antibody produced during the **primary immune response** to a new pathogen. - Although it indicates an immediate immune reaction, it is gradually replaced by IgG in the later stages and during secondary responses. *IgE* - **Immunoglobulin E (IgE)** is primarily involved in **allergic reactions** and defense against **parasites**. - Its levels significantly increase during these specific conditions, but it does not play a major role in a typical secondary immune response to common pathogens.

Q: Which of the following diseases is not associated with congenital passive immunity?

Pertussis. ***Pertussis*** - While maternal antibodies can be passed to the fetus, the protection against **pertussis (whooping cough)** is generally **incomplete and short-lived**, making it a disease where congenital passive immunity is often insufficient. - Infants remain vulnerable to severe pertussis despite maternal antibodies, necessitating early vaccination (starting at 6 weeks of age). - This is why **maternal immunization during pregnancy** (Tdap vaccine) is now recommended to boost antibody levels. *Tuberculosis* - While maternal antibodies to *Mycobacterium tuberculosis* antigens may cross the placenta, they provide **minimal to no protective immunity** against TB. - TB immunity is predominantly **cell-mediated (T-cell based)** rather than antibody-mediated, so passive transfer of IgG offers little clinical protection. - However, **BCG vaccination at birth** can provide some protection, and maternal antibodies are generally considered to transfer, making TB traditionally included in diseases with some degree of congenital passive immunity transfer (even if not highly protective). *Rubella* - **Maternal IgG antibodies** against **rubella** virus are efficiently transferred across the placenta, conferring **strong and long-lasting passive immunity** to the newborn. - This protection typically lasts for several months, preventing rubella infection in infancy. *Measles* - Babies born to mothers immune to measles receive **maternal antibodies** that provide **excellent passive immunity** for the first 6-9 months of life. - This congenital protection is crucial for preventing measles in early infancy before the first routine measles vaccine is administered (at 9 months in India).

Question 1

Which of the following is not considered an antigen-presenting cell?

Accepted Answer

Thymocytes

Answer

Macrophages

Answer

Langerhans cells

Answer

B lymphocytes

Question 2

Viral infection is differentiated from bacterial infection by:

Accepted Answer

Interferon production

Answer

Toxin production

Answer

Lymphocytosis

Answer

Neutrophilia

Question 3

Adoptive immunity is by what mechanism?

Accepted Answer

Injection of lymphocytes

Answer

Vaccination with killed pathogens

Answer

Natural infection

Answer

Passive transfer of antibodies

Question 4

A 62-year-old woman presents with fever, cough, sputum production, and pleuritic chest pain. Chest X-ray reveals a right middle lobe infiltrate, and she is started on antibiotics for the treatment of pneumonia. Her sputum Gram stain is positive for S. pneumoniae. Which of the following immunologic mechanisms is the most specific host defense against pneumococcal infection?

Accepted Answer

IgG antibody directed against capsular antigens

Answer

complement system activity

Answer

macrophage activity in the alveoli

Answer

functional splenic activity

Question 5

An 80-year-old woman, a retirement home resident, has multiple bouts of pneumonia caused by Streptococcus pneumoniae. In an attempt to prevent such infections, polyvalent vaccines directed at multiple serotypes of the organism have been administered but have not elicited long-acting immunity. Which of the following is the probable explanation for this phenomenon?

Accepted Answer

Memory T lymphocytes respond poorly to polysaccharide antigens.

Answer

The bacterial capsule binds C3b, facilitating activation of the alternative complement pathway, inducing complement-mediated lysis, and preventing immunization.

Answer

The capsular polysaccharides of S. pneumoniae have limited hapten potential.

Answer

S. pneumoniae evades host immune response by forming capsular coatings composed of host proteins and recognized as "self" antigens.

Question 6

All of the following forces are involved in antigen-antibody reactions, except:

Accepted Answer

Covalent bond

Answer

Electrostatic bond

Answer

Hydrogen bond

Answer

Van der Waals forces

Question 7

Congenital passive immunity is INADEQUATE in -

Accepted Answer

Pertussis

Answer

Measles

Answer

Mumps

Answer

RSV (Respiratory Syncytial Virus)

Question 8

Which type of antibody is primarily involved in the secondary immune response?

Accepted Answer

IgG

Answer

IgA

Answer

IgM

Answer

IgE

Question 9

Which of the following diseases is not associated with congenital passive immunity?

Accepted Answer

Pertussis

Answer

Measles

Answer

Tuberculosis

Answer

Rubella

Immunology — MCQs

Immunology — MCQs

On this page

Practice by Chapter

Want unlimited practice?