CMT Immunology & Serology 2

Question 1

Which component binds antigen-antibody complexes to initiate the classical complement pathway?

Accepted Answer

C1q

Answer

C1q binds the Fc regions of IgM or at least two adjacent IgG molecules, which starts the classical pathway.

Question 2

The membrane attack complex (MAC) is made up of which complement components?

Accepted Answer

C5b-C9

Answer

C5b, C6, C7, C8, and multiple C9 molecules assemble into a pore that lyses the target cell.

Question 3

A patient has an anaphylactic reaction to a bee sting. Which antibody class mediates this reaction?

Accepted Answer

IgE

Answer

Type I hypersensitivity happens when IgE bound to mast cells crosslinks with allergen and triggers histamine release.

Question 4

Serum sickness is a classic example of which type of hypersensitivity?

Accepted Answer

Type III

Answer

Serum sickness happens when immune complexes deposit in tissues and activate complement, which is the Type III mechanism.

Question 5

A positive tuberculin (PPD) skin test read at 48-72 hours shows which type of hypersensitivity?

Accepted Answer

Type IV, T cell-mediated

Answer

Delayed-type hypersensitivity is driven by sensitized T cells and macrophages, not by antibody.

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