Humoral immunity

Question 1

What is the humoral immune system?

Answer 1

A component of the immune system that involves antibodies produced by B cells to fight infections

Question 2

What are acute-phase proteins?

Answer 2

Plasma proteins produced by the liver during inflammation that mimic antibodies and aid in immune responses

Question 3

What are some examples of acute-phase proteins?

Answer 3

C-reactive protein for opsonization and complement activation and haptoglobin for binding hemoglobin

Question 4

What is the role of complement proteins?

Answer 4

They enhance immune responses by opsonizing pathogens promoting inflammation and forming the membrane attack complex MAC

Question 5

What are the three pathways of complement activation?

Answer 5

The classical pathway the alternative pathway and the lectin-binding pathway

Question 6

What triggers the classical pathway?

Answer 6

Binding of antibodies such as IgM or two IgG molecules to antigens on the pathogen surface

Question 7

What triggers the alternative pathway?

Answer 7

Direct activation by microbial surfaces such as lipopolysaccharides LPS or aggregated IgA

Question 8

What triggers the lectin-binding pathway?

Answer 8

Binding of mannose-binding lectin MBL to carbohydrate structures on the surface of pathogens

Question 9

What are the main steps in the classical complement pathway?

Answer 9

C1 binds to antibodies followed by activation of C4 and C2 forming C3 convertase which cleaves C3 into C3a and C3b

Question 10

What is the role of C3 convertase?

Answer 10

It cleaves C3 into C3a and C3b initiating amplification of the complement cascade

Question 11

What happens to C3b after it is formed?

Answer 11

C3b binds to pathogen surfaces aiding in opsonization and forming C5 convertase

Question 12

What is the role of C5 convertase?

Answer 12

It cleaves C5 into C5a a chemoattractant and C5b which initiates the formation of the membrane attack complex MAC

Question 13

What is the membrane attack complex MAC?

Answer 13

A structure formed by C5b C6 C7 C8 and multiple C9 molecules that creates pores in the membrane of pathogens causing osmotic lysis

Question 14

What is the role of C3a and C5a in the complement pathway?

Answer 14

They act as chemoattractants recruiting immune cells to the site of infection and enhancing inflammation

Question 15

What is the difference between opsonization and lysis in the complement system?

Answer 15

Opsonization involves coating pathogens with C3b to enhance phagocytosis while lysis involves the destruction of pathogens via the MAC

Question 16

What is the role of mannose-binding lectin MBL in the lectin pathway?

Answer 16

It binds to mannose residues on pathogen surfaces activating a cascade similar to the classical pathway

Question 17

What is the role of C4 and C2 in the classical and lectin pathways?

Answer 17

C4 and C2 are cleaved to form C3 convertase which is central to complement activation

Question 18

What is the role of factor B in the alternative pathway?

Answer 18

Factor B binds to C3b on pathogen surfaces and is cleaved by factor D to form an alternative C3 convertase

Question 19

What is the role of factor D in the alternative pathway?

Answer 19

Factor D cleaves factor B when it is bound to C3b forming the C3 convertase in the alternative pathway

Question 20

What is the importance of complement regulation?

Answer 20

To prevent excessive activation and damage to host tissues

Question 21

What are some key complement regulators?

Answer 21

Complement inhibitors such as C1 inhibitor decay-accelerating factor DAF and CD59 protect host cells

Question 22

What is the role of C3b in opsonization?

Answer 22

C3b coats the pathogen surface making it easier for phagocytes to recognize and engulf the pathogen

Question 23

What is the role of complement in inflammation?

Answer 23

Complement components like C3a and C5a recruit immune cells and increase vascular permeability to enhance the immune response

Question 24

What is the role of C5b in the complement cascade?

Answer 24

C5b binds to C6 and C7 initiating the assembly of the MAC

Question 25

What are the terminal steps of the complement cascade?

Answer 25

C5b recruits C6 C7 C8 and multiple C9 molecules to form the MAC which creates pores in the pathogen membrane

Question 26

What is the significance of the complement system in humoral immunity?

Answer 26

It enhances the effectiveness of antibodies by promoting pathogen destruction opsonization and immune cell recruitment

Question 27

How does complement activation link the innate and adaptive immune systems?

Answer 27

Complement bridges innate and adaptive immunity by amplifying antibody responses and directly targeting pathogens for destruction

Question 28

What is the primary role of IgM in humoral immunity?

Answer 28

It is the first antibody produced in infections and is efficient at activating the complement system

Question 29

What is the primary role of IgG in humoral immunity?

Answer 29

It provides long-term immunity neutralizes pathogens and enhances phagocytosis

Question 30

What is the primary role of IgA in humoral immunity?

Answer 30

It protects mucosal surfaces by neutralizing pathogens and preventing their attachment

Question 31

What is the primary role of IgE in humoral immunity?

Answer 31

It mediates allergic responses and provides defense against parasites

Question 32

What are the outcomes of complement activation?

Answer 32

Pathogen lysis immune cell recruitment and enhanced phagocytosis

Question 33

What is antibody-dependent cellular cytotoxicity ADCC?

Answer 33

A process where antibodies recruit natural killer cells to destroy target cells

Question 34

How do IgM and IgG differ in complement activation?

Answer 34

IgM is more efficient in activating the complement system while IgG subclasses vary in their efficiency

Question 35

What is the importance of acute-phase proteins during infections?

Answer 35

They act as diagnostic markers of inflammation and enhance immune responses

Question 36

What is the role of antibodies in neutralization?

Answer 36

They block pathogens from binding to host cells and neutralize toxins

Question 37

What are the differences between the three complement pathways?

Answer 37

The classical pathway is antibody-dependent the alternative pathway is triggered by microbial surfaces and the lectin pathway is triggered by MBL binding

Question 38

What are the effector functions of antibodies in humoral immunity?

Answer 38

Neutralization opsonization complement activation and recruiting immune cells

Question 39

What is the order of the classical complement pathway?

Answer 39

1- Initiation: C1q binds to antigen-antibody complexes (e.g., IgM or IgG bound to antigens). 2- Activation of C1 Complex: C1r and C1s are activated, leading to cleavage of C4 into C4a and C4b. 3- Formation of C3 Convertase: C4b binds to the pathogen surface and combines with C2a, forming the C4b2a complex (C3 convertase). 4- C3 Activation: C3 convertase cleaves C3 into C3a (inflammatory mediator) and C3b (opsonin). 5- Formation of C5 Convertase: C3b joins C4b2a to form C5 convertase. 6- MAC Formation: C5 convertase cleaves C5 into C5a (chemoattractant) and C5b, initiating the assembly of the membrane attack complex (MAC).

Question 40

What is the order of the alternative complement pathway?

Answer 40

1- Spontaneous Hydrolysis of C3: C3 undergoes spontaneous hydrolysis to C3(H2O). 2- Formation of C3 Convertase: C3(H2O) binds factor B, which is cleaved by factor D to form the alternative C3 convertase (C3bBb). 3- Amplification Loop: C3 convertase generates additional C3b, which can further amplify complement activation. 4- Formation of C5 Convertase: Additional C3b binds to C3 convertase, forming the alternative C5 convertase. 5- MAC Formation: Similar to the classical pathway, C5b initiates the assembly of the MAC.

Question 41

What is the order of the lectin binding pathway?

Answer 41

1- Initiation: Mannose-binding lectin (MBL) binds to mannose residues on pathogens. 2- Activation of MASPs: MBL-associated serine proteases (MASPs) cleave C4 and C2, forming C3 convertase (C4b2a). 3- C3 Activation: Similar to the classical pathway, C3 convertase cleaves C3 into C3a and C3b. 4- Formation of C5 Convertase: C3b binds to C3 convertase, forming C5 convertase. 5- MAC Formation: C5b initiates the assembly of the MAC.