Infection: The adaptive immune response

Question 1

What are the different types of antigen presenting cells? Where are they found and what cell type do they present to?

Answer 1

Dendritic cells: found in lymph nodes, mucous membranes and blood. They present to T and B cells.

Macrophages: present in many tissues, and present to T cells.

B cells: present in lymphoid tissue, and present to T cells

Question 2

What are the 2 types of major histocompatibility complex and what are their roles?

Answer 2

Class 1 MHC: found on all nucleated cells, and present antigens from intracellular microbes.
Class 2 MHC: found on antigen presenting cells (dendritic, macrophages, B cells) and present antigens from extracellular microbes.

Question 3

Which T cells (and receptors) do the 2 types of MHC molecule bind to?

Answer 3

MHC class 1 binds to the CD8 receptor on T killer cells (MHC class 1 presents antigens from intracellular microbes so is therefore infected and the whole cell needs to be destroyed)

MHC class 2 binds to the CD4 receptor T helper cells to lead to activation of the B cells to destroy the pathogen

Question 4

What are some clinical problems with MHC molecules?

Answer 4

MHC mismatch is a major cause of organ transplant rejection.
Certain types of MHC predispose to autoimmune disease eg ankylosing spondylitis

Question 5

What is the role of T helper cells?

Answer 5

They enhance the immune response by activating B cells, T killer cells and macrophages.

They cause proliferation and differentiation of B cells into either plasma cells (secrete antibodies) or memory B cells for second exposure to the pathogen.

Question 6

What is the role of antibodies?

Answer 6

1. Neutralise the pathogen
2. Opsonisation
3. Activate the compliment pathway

Question 7

What is the structure of an antibody?

Answer 7

There is a constant region - determines which type of antibody it is eg IgM IgA
There is a variable region which is adapted to be specific to each different antigen