(L26) CIS - Lymphocyte Activation

Question 1

What is hyper IgM syndrome (HIGM) and what is characteristic of it and what is the cause?

L26 S38

Answer 1

Characteristics:

• elevated IgM
• reduced IgG, IgA, and IgE (failure of class switching)
• thrombocytopenia

Causes:

• deficient CD40L (X-linked)
• deficient CD40
• deficient AID
• deficient UNG

Question 2

What differences are seen in HIGM due to CD40L deficiencies and AID deficiencies?

L26 S40

Answer 2

Without CD40L, B cells are retained in the lymph node as they do not receive activating signals. This results in enlarge lymph nodes and and sensitivity to opportunistic infections as the B cells are not in circulation to fight infections.

These two features are not present in B cells without AID as they receive activating signals still so they leave the lymph nodes and fight infections.

Question 3

What are examples of opportunistic infections?

L26 S48

Answer 3

• candida
• C. difficle
• Pneumocystis jiroveci
• cryptosporidium
• toxoplasma Gondi
• cytomegalovirus

Question 4

What cytokine promotes switching from Th2 response to Th1 response?

L26 S56

Answer 4

IFN-γ

Inhibits type 2 response; stimulates type 1 response, activates macrophages

Question 5

What is toxic shock syndrome?

L26 S68-69

Answer 5

Caused by superantigens binding to β chain of TCR with high affinity causing excessive activation.