Immunology Exam 3

What are the three pathways of the complement system?

Classical, MB Lectin, and Alternative pathways.

What are the functions of the complement system?

The complement system enhances the immune response by promoting inflammation, opsonizing pathogens for phagocytosis, and directly lysing microorganisms through the formation of the membrane attack complex.

What is the difference between humoral and adaptive immunity?

Humoral immunity involves the production of antibodies by B cells, while adaptive immunity encompasses the entire immune response, including both humoral and cell-mediated components, primarily involving T cells.

List and describe the functions of the complement system.

Opsonization (pathogens are coated by C3b making them easier for phagocytes to recognize and engulf), chemotaxis (complement proteins like C3b and C5a attract immune cells to the site of infection), cell lysis (the complement system can directly attack and destroy pathogens by forming a membrane attack complex that forms pores in the pathogen cell membrane), and agglutination (antibodies cause agglutination forming clumps that are more easily ingested by phagocytes reducing the number of infectious units the immune system must deal with).

Describe the general characteristics of components of the complement system.

Protect from infection, remove particular substances, and help modulate adaptive immune responses.

The >25 components of the complement system can be categorized into functional
protein classes. List and describe these classes of proteins. ins.

• activation pathways

  • C1, C3, C5, convertases

• opsonization and phagocytosis

  • C3b, C4b

• chemotaxis

  • C3a, C5a

• regulations

  • C6, C7, C8, C9 (MAC)

Differentiate between the passive and active mechanisms of complement regulation.
Why is regulating this pathway so important?

• Passive: regulatory proteins

• Active: spontaneous inactivation of components.

• Prevents it from getting out of control.

Describe the membrane attack complex (MAC). Why is it so effective at cytolysis?

The membrane attack complex (MAC) is typically formed on the surface of pathogenic bacterial cells as a result of the activation of the host's alternative pathway, classical pathway, or lectin pathway of the complement system, and it is one of the effector proteins of the immune system. The membrane-attack complex (MAC) forms transmembrane channels. These channels disrupt the phospholipid bilayer of target cells, leading to cell lysis and death.

Describe mechanisms microbes have evolved to evade complement-mediated damage.

• 1. capsule-outer polysaccharide coating that's outside of the cell wall prevents MAC binding.

• 2. Elastase-enzyme that is protease evades host system by destroying (breaking down) complement protein.

• 3. LPS (long polysaccharide chains) prevent MAC formation.

• 4. molecular mimicry- molecule is similar to one of the regulatory proteins.

How do the innate immune response and the complement system relate to one another?

The complement system is a part of the immune system that helps or complements the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is also part of the innate immune system.

What are the major groups of pathogens?

• Viruses- influenza

• Bacteria- smallpox

• Fungi- ringworm

• Parasites- malaria

n general, why are infectious diseases such a huge problem world wide?

Infectious diseases pose a major global health threat due to factors like rapid population growth, increased human mobility, urbanization, and the emergence of new pathogens, as well as the re-emergence of old ones, leading to widespread outbreaks and pandemics.

What is the basic structure of a virus?

Genetic material (DNA) enclosed within a protein coat called a capsid.

Explain the viral replication process, in generic terms.

Attachment
Penetration
Uncoating
Replication
Assembly
Release

Describe the host immune response to viral infection. Be sure to discuss the innate
response as well as the humoral and cell-mediated adaptive responses. What role do
INF- and INF- play in host antiviral activity?

- inhibition of viral infection via type I interferons
- NK-cell mediated killing of infected cells

The humoral response (or antibody‐mediated response) involves B cells that recognize antigens or pathogens that are circulating in the lymph or blood ("humor" is a medieval term for body fluid). The response follows this chain of events:

The cell‐mediated response involves mostly T cells and responds to any cell that displays aberrant MHC markers, including cells invaded by pathogens, tumor cells, or transplanted cells. The following chain of events describes this immune response:

Describe mechanism viruses have evolved to evade complement-mediated damage. (This question comes from the complement system objectives!). Provide examples of mechanisms that viruses use to evade the host immune system.

Host defence system= multistep, sequential intercommunication

Summarize the host immune response to extracellular bacterial infection. Provide specific examples of how the host immune system responds to the four primary steps in bacterial infection and how bacteria may evade those host immune responses.

nonspecific mechanisms, innate immune responses, and adaptive immune responses.

The incubation period (silent stage-the pathogen has gained entry into the host and starts replicating) is the period between exposure to a pathogen and when symptoms and/or signs are first apparent. This phase signifies the period taken by the multiplying organism to reach a population necessary to produce symptoms in the host.

The prodromal period (itchy, runny nose, dry eyes)of infectious illness is the period between the end of the incubation period and the point at which the characteristic symptoms of the illness appear. A person in the prodromal stage of an infectious illness often displays nonspecific symptoms, such as fatigue or malaise.

The acute period (the disease reaches its highest point of development, severe aches, chills, vomiting) is the phase of rapid multiplication of the pathogen with exponential growth and peak in its' population. Symptoms are very pronounced, both specific to the organ affected as well as in general due to the strong response of the immune system.

Convalescence period is the time the host recovers gradually and returns to baseline. The pathogen load starts to decline, but may not be completely eliminated immediately, hence the host may continue to be a source of infection even if feeling better.


1. Limit viral replication and gene expression - innate defense: interferon and apoptosis

2. Capture and destroy all virus - Innate defense: phagocytosis and complement/ Acquired immunity: antibodies

3. Kill virus infected cells - Innate defense: NK cells/Acquired cellular immunity CTLs

4. Prevent reinfection - memory: antibody and T cells