Insufficient or Overactive Immune Response

Question 1

Describe Severe Combined Immunodeficiency (SCID)

Answer 1

• X-chromosome linked disease, therefore more common in XY-males.
  Note: XX-females are ‘carriers’
  Patients lack functional T cells and B cells.

Question 2

Describe Virus-induced immune suppression

Answer 2

• Measles, HIV and many other viruses interfere with normal host immune system
• HIV targets and can kill CD4 T cells
• This leads to a diminished level of CD4 T cells unable to provide “help” for antibody and cytotoxic response

Question 3

Describe Human immunodeficiency Virus (HIV)

Answer 3

• HIV-receptor is CD4 molecule on CD4 T cells
• Infection leads to loss of CD4 T cells
• CD4 T cells help both humeral (B cell/antibody) and cytotoxic responses,
• HIV infection impacts on immunity to microbes (fungi, bacterial and virus)

Question 4

Describe autoimmune disease

Answer 4

• Normally prevented by host mechanisms of immune tolerance
• Although the innate system can trigger autoimmunity or exacerbate autoimmunity
• Autoimmune attack is mediated by the adaptive immune response

Question 5

Describe immune tolerance

Answer 5

• Immune tolerance is critical to avoid autoimmunity
• The thymus to delete auto reactive (self-reactive) T cells
• In the periphery there are other mechanisms to ensure that auto-reactive T and B cells are silenced
• Failures (due to your genes or triggering infection) in immune tolerance can lead to autoimmunity

Question 6

Describe rheumatoid arthritis (RA)

Answer 6

It is an autoimmune disorder that primarily affects joints
- Autoreactive T cell and B cells attack self-antigens present in the joints

Question 7

Describe Type I Diabetes

Answer 7

Beta islet cells are attacked, causing a low secretion of insulin.
The other cells remain unharmed, which shows how specific this is.

Question 8

Describe allergic reactions

Answer 8

• ‘Allergens’ are the antigens that trigger allergy
• Are normally ‘harmless’ environmental antigens: non-toxic plant, animal or other food materials
• Chemicals can induce allergy (eg. penicillin)
• Range of outcomes: from hay fever to systemic anaphylaxis

Question 9

Describe the actual allergic response

Answer 9

• Dendritic cells present peptides from peanut proteins (allergens) to (CD4) helper T cells
• Primed helper T cells activate B cells to become plasma cells that secrete IgE (and some B cells will class switch to IgE)
• Secreted IgE binds to mast cell receptors (FcR)
• Binding of peanut proteins to FcR on mast cells triggers mast cell degranulation and release of histamine and other inflammatory regulators.

Question 10

Describe Fc receptors

Answer 10

• Fc receptors (FcR) bind to the Fc domain (on constant region) of antibody. FcR facilitate a number of functions, including phagocytosis and mast cell activation.
• The Fc portion of the antibody is the part that will bind to the Fc receptors and is part of the constant region that may undergo class switching during immune response.

Question 11

Describe the order of events for changes in antibody structure

Answer 11

1. The antigen binding sites (top ‘arm’ bits of the Y shape) are rearranged in bone marrow (during generation of diversity)
2. Constant region (bottom part of Y shape) may switch during immune response