The Alternative Pathway in Immunity

Which complement protein is primarily responsible for inactivating C1r and C1s, thereby halting the classical pathway?

C4b-binding protein (C4BP)
Membrane cofactor protein (MCP)
Complement receptor type 1 (CR1)
C1-inhibitor (C1INH) (correct)

Which complement regulator is the most efficient cofactor for factor I-mediated cleavage of C3b?

Decay accelerating factor (DAF)
C4b-binding protein (C4BP)
Membrane cofactor protein (MCP) (correct)
Complement receptor type 1 (CR1)

Which complement regulator can dissociate C4b2a complexes, thereby causing the cessation of the classical pathway?

C4b-binding protein (C4BP) (correct)
Membrane cofactor protein (MCP)
Decay accelerating factor (DAF)
Complement receptor type 1 (CR1)

Which complement regulator is found on virtually all epithelial and endothelial cells, except erythrocytes?

Membrane cofactor protein (MCP) (A) Signup and view all the answers

Which complement regulator is a large polymorphic glycoprotein found mainly on peripheral blood cells?

Complement receptor type 1 (CR1) (C) Signup and view all the answers

Which complement regulator is capable of combining with either fluid-phase or bound C4b, to prevent C4b from binding to C2?

C4b-binding protein (C4BP) (C) Signup and view all the answers

What is the main function of the Membrane Inhibitor of Reactive Lysis (MIRL) or CD59?

To bind to C8 and prevent insertion of C9 into host cell membranes (C) Signup and view all the answers

What is the role of the S protein (also known as vitronectin) in the regulation of terminal complement components?

It interacts with the C5b67 complex and prevents it from binding to cell membranes (B) Signup and view all the answers

Which of the following is true about the complement receptors found on host cells?

They amplify and enhance the immune response by augmenting phagocytosis and stimulating accessory cells (A) Signup and view all the answers

What is the relationship between the activation of complement and the inflammatory response?

Activation of complement is a very effective means of amplifying the inflammatory response to destroy and clear foreign antigens (A) Signup and view all the answers

Which of the following is a function of the Membrane Inhibitor of Reactive Lysis (MIRL) or CD59?

To bind to C8 and prevent the insertion of C9 into host cell membranes (A) Signup and view all the answers

What is the role of complement proteins in the immune system?

Complement proteins serve as a means of linking innate and natural immunity, as well as amplifying the inflammatory response to destroy and clear foreign antigens (B) Signup and view all the answers

What is the function of Factor D in the complement system?

To cleave factor B into two pieces (A) Signup and view all the answers

Which of the following is NOT a triggering substance for the alternative pathway of complement activation?

Lectins (A) Signup and view all the answers

What is the role of lectins in the lectin pathway of complement activation?

Recognize carbohydrates on microbial cell walls (C) Signup and view all the answers

What is the main difference between the lectin pathway and the alternative pathway of complement activation?

Involvement of lectins (A) Signup and view all the answers

Why is Factor D essential in the complement system?

To cleave factor B, initiating complement activation (B) Signup and view all the answers

What distinguishes the mannose-binding lectin pathway from the other complement pathways?

Carbohydrate recognition by lectins (A) Signup and view all the answers

What is the primary function of mannose-binding lectin (MBL) in the lectin pathway?

To bind to mannose or related sugars found on the surface of pathogens, initiating the lectin pathway (A) Signup and view all the answers

Which of the following statements about MBL is correct?

MBL deficiencies have been associated with serious infections in neonates and infants (A) Signup and view all the answers

Which of the following MBL-associated serine proteases (MASPs) is involved in the activation of the lectin pathway?

MASP-2 (B) Signup and view all the answers

What is the primary function of C1 inhibitor (C1INH) in the complement system?

To inhibit the activation of the classical and lectin pathways at the first stages (A) Signup and view all the answers

What is the primary reason for the regulation of the complement system?

To ensure that the reaction remains localized and infectious agents, not self-antigens, are destroyed (B) Signup and view all the answers

Which of the following statements about the lectin pathway is correct?

The lectin pathway is initiated by the binding of MBL to mannose or related sugars found on pathogens (B) Signup and view all the answers

What is the main role of opsonins in the immune response?

Facilitating destruction by phagocytic cells (A) Signup and view all the answers

Which complement protein is considered the most potent anaphylatoxin?

C5a (C) Signup and view all the answers

What effect does binding of C5a to basophils and mast cells have?

Increasing vascular permeability and causing smooth muscle contraction (C) Signup and view all the answers

Which cells does C5a act as a chemotaxin for?

Neutrophils, basophils, and eosinophils (C) Signup and view all the answers

Which effector molecules are produced by neutrophils upon C5a binding?

Oxygen radicals and hydrolytic enzymes (A) Signup and view all the answers

How do anaphylatoxins contribute to the immune response?

Increasing vascular permeability (D) Signup and view all the answers