KMU Past Paper Practice

Question:

A 19-year-old medical student receives a vaccine containing microbial antigen. Several weeks later, antigen-specific antibodies and memory lymphocytes can be demonstrated. Which type of immunity has been produced?

Options:

Correct Answer: Artificial active immunity

Explanation: Vaccination introduces antigen deliberately and stimulates the recipient’s own lymphocytes, producing both an immune response and immunological memory.

Question:

A patient receives a preparation containing preformed antibodies after a potentially dangerous toxin exposure. Protection begins rapidly but does not produce long-term immunological memory. Which form of protection is illustrated?

Options:

Correct Answer: Artificial passive immunity

Explanation: Administration of preformed antibodies gives immediate artificial protection, but the recipient’s lymphocytes are not activated sufficiently to establish memory.

Question:

During the early phase of a viral infection, several infected cells reduce expression of normal MHC class I molecules. A lymphoid cell recognizes this abnormal pattern and destroys the affected cells before a specific adaptive response is fully established. Which cell is responsible?

Options:

Correct Answer: Natural killer cell

Explanation: Natural killer cells are innate lymphoid cells that can detect abnormal host cells, including cells with reduced normal MHC class I expression, without antigen-specific T-cell receptors.

Question:

A bone marrow disorder damages the common precursor responsible for production of both myeloid and lymphoid immune-cell lineages. Which cell has been primarily affected?

Options:

Correct Answer: Hematopoietic stem cell

Explanation: Hematopoietic stem cells in bone marrow are the common precursors from which both myeloid and lymphoid immune-cell lineages develop.

Question:

A tissue leukocyte engulfs bacteria, removes necrotic material, releases inflammatory mediators and can display processed microbial antigen to T lymphocytes. Which cell best fits these combined functions?

Options:

Correct Answer: Macrophage

Explanation: Macrophages combine phagocytosis, removal of damaged material, inflammatory mediator production and antigen presentation, linking innate and adaptive responses.

Question:

A soluble bacterial protein enters a lymphoid follicle. One lymphocyte binds the intact three-dimensional protein directly through membrane immunoglobulin without requiring prior peptide presentation. Which mode of recognition is being demonstrated?

Options:

Correct Answer: Direct recognition of native antigen

Explanation: B-cell receptors are membrane immunoglobulins capable of binding many antigens in their native form, unlike T-cell receptors that recognize processed peptide-MHC complexes.

Question:

A large microbial protein contains several small regions that are recognized independently by different lymphocyte clones. What is the term for each individual recognizable region?

Options:

Correct Answer: Epitope

Explanation: An epitope is the specific antigenic determinant recognized by an individual antibody or lymphocyte receptor; one complex antigen may contain several epitopes.

Question:

Flow cytometry of mature naïve B lymphocytes demonstrates a surface immunoglobulin class that functions mainly as an antigen receptor together with surface IgM. Which immunoglobulin is being detected?

Options:

Correct Answer: IgD

Explanation: IgD is expressed mainly on mature naïve B cells, where it functions as a membrane antigen receptor together with IgM.

Question:

A 21-year-old woman develops wheezing, itching and urticaria shortly after exposure to an allergen. The responsible antibody is bound with high affinity to receptors on mast cells before the exposure occurs. Which immunoglobulin class mediates this reaction?

Options:

Correct Answer: IgE

Explanation: IgE binds strongly to mast cells and basophils; subsequent allergen-mediated cross-linking can trigger rapid release of inflammatory mediators.

Question:

Serum obtained early during an antibody response contains a large polymeric immunoglobulin that is particularly efficient at initiating the antibody-dependent complement cascade. Which class best fits this description?

Options:

Correct Answer: IgM

Explanation: Secreted IgM is pentameric and is an important early antibody; its structure makes it particularly effective at activating the classical complement pathway.

Question:

Tumor cells in a laboratory preparation are first coated with specific antibody. Effector leukocytes then attach to the antibody-coated cells through receptors for the antibody constant region and kill the target. Which antibody function is demonstrated?

Options:

Correct Answer: Antibody-dependent cellular cytotoxicity

Explanation: In antibody-dependent cellular cytotoxicity, an effector cell recognizes the Fc portion of antibody coating a target and then contributes to target-cell destruction.

Question:

A bacterial antigen in plasma becomes coated with specific antibody. A complement component then binds to the antigen-antibody complex and initiates a cascade that ultimately activates C3. Which pathway has been initiated?

Options:

Correct Answer: Classical pathway

Explanation: The classical pathway is characteristically initiated when complement interacts with antibody bound to antigen, linking humoral adaptive immunity with complement.

Question:

Complement activation during an acute inflammatory response generates a small C3-derived fragment that promotes inflammatory mediator release and increases vascular reactions. Which fragment is responsible?

Options:

Correct Answer: C3a

Explanation: C3a is a soluble inflammatory complement fragment that promotes mediator release and vascular changes, whereas C3b remains an important surface-bound opsonin.

Question:

Electron microscopy of a complement-sensitive bacterial cell shows circular pores forming in its plasma membrane after terminal complement activation. Which complex directly produces these membrane defects?

Options:

Correct Answer: C5b-C9 membrane attack complex

Explanation: C5b recruits C6-C9 to form the membrane attack complex, which creates pores in susceptible membranes and can produce cell lysis.

Question:

A young woman has recurrent manifestations caused by deposition of antigen-antibody complexes. Testing suggests defective clearance of these complexes rather than a defect of the terminal lytic pathway. Deficiency of which group of complement proteins best explains this pattern?

Options:

Correct Answer: Early classical components C1-C4

Explanation: Deficiency of early classical components, particularly C1, C2 or C4, impairs immune-complex handling and is associated with lupus-like immune-complex disease.

Question:

A patient with severe chronic hepatic dysfunction is found to have reduced concentrations of several circulating complement proteins. Which organ normally provides the major source of these plasma proteins?

Options:

Correct Answer: Liver

Explanation: The liver is the principal source of many circulating complement proteins, although some immune and tissue cells can also produce complement locally.

Question:

A normal host cell is exposed to activated complement but avoids progressive amplification because a surface protein accelerates the breakdown of C3/C5 convertase complexes. Which regulator performs this protective function?

Options:

Correct Answer: CD55

Explanation: CD55, also called decay-accelerating factor, protects host cells by promoting dissociation of complement convertase complexes.

Question:

During complement activation, C3b is generated continuously. On normal host surfaces, two regulatory proteins work together to limit persistence and activity of this fragment. Which pair provides this control?

Options:

Correct Answer: Factors H and I

Explanation: Factors H and I regulate C3b and help prevent inappropriate amplification of complement on normal host-cell surfaces.

Question:

A naïve T lymphocyte binds its specific peptide-MHC complex on an antigen-presenting cell, but the cell fails to receive the additional activation signal required for a full response. Which process is missing?

Options:

Correct Answer: Co-stimulation

Explanation: Antigen recognition gives T-cell specificity, but naïve T cells also require a co-stimulatory signal for effective activation and subsequent clonal expansion.

Question:

A culture contains thousands of lymphocytes with different antigen receptors. After addition of one defined antigen, only a small matching population becomes activated and proliferates extensively. Which principle of adaptive immunity does this experiment demonstrate?

Options:

Correct Answer: Clonal selection

Explanation: An antigen selects pre-existing lymphocytes with matching receptors; those specific clones then proliferate to generate the focused adaptive immune response.