Immunology & Serology Flashcards

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

Answer: C1q

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

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

Answer: C5b-C9

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

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

Answer: IgE

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

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

Answer: Type III

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

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

Answer: Type IV, T cell-mediated

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

To inactivate complement in a patient serum sample before certain serologic tests, the serum is heated to:

Answer: 56°C for 30 minutes

Heating to 56°C for 30 minutes destroys heat-labile complement components (mainly C1 and C2) without denaturing antibody.

Which immunoglobulin class crosses the placenta and gives the newborn passive immunity?

Answer: IgG

IgG is the only immunoglobulin actively carried across the placenta, through the neonatal Fc receptor (FcRn).