adaptive immune response

Describe the structure and function of lymph nodes

• Afferents lymphatic = antigens arrive from antigen-presenting cells and activate T and B cells - produce antibodies

• Efferent lymphatic = antibodies exit

• Non lymphoid cells pass through blood vessels

• Lymphoid cells move from blood to lymph nodes through high Endocytic venules

What to B and Th lymphocytes do

• Have antigen receptors on their surface

• Each cell has 1 type of receptor

  • Each receptor is specific for 1 antigen

    • Different from PRRs that recognise generic molecules

Describe the process of lymphoid circulation

• Dendritic cells arrive in lymph

  • Loaded with antigens to present to B and T cells

• B and T cells arrive from blood - each with its own receptor

  • Waiting to be activated by an antigen on the dendritic cells

• B cells move to the follicle = gets activated by antigen presenting dendritic cells

• T cells also get activated

  • Activated T cell interacts with activated B cell (cytokines) to stimulate it

  • B cell makes antibodies

How is the germinal centre formed

1. B cells leave blood and form primary follicles —> controlled by Chemokines

2. Antigen and lymph cells enter node via afferents lymphatic

3. Ag activated B cells move under Chemokines control to the T/B zone border and proliferate

4. Germinal centre = a short but intense proliferation

5. B cells released by germinal centre differentiate into plasma and memory cells

How is colonial selection achieved

• Without activation, lymphocytes tend to die via apoptosis

  • To proliferate, B cell needs to bind an antigen and receive stimulation from Th cells B

• Primary immune response occurs on the first occasion a pathogen is encountered

  • Occurs in secondary lymphoid organs

• Pathogen is phagocytoed by a macrophage

• Macrophage activates Th cells

  • Activate B lymphocytes = clinal expansion produces antibodies

  • Natural killer cells

Importance of antigen-receptor variability

Recognise a wide variety of potential pathogens

Generated via:

• V(D)J recombination - random arrangement of:

  • V = variable

  • J = joining gene segments

  • D =

    • T cells receptor beta chain

    • B cell receptor heavy chain

• Junctional diversity

  • Additional/removal of nucleotides at the junctions between gene segments during recombination

• Somatic hypermutation

  • Introduction of point mutations in the variable regions of antibody genes

Self tolerance

Ability of immune system to recognise and not react against the body’s own antigens

Describe the selectivity of self tolerance

Positive selection:

• T cells whose receptors can bind to self-MHC molecules with low affinity

Negative selection

• T/B cells whose receptors bind strongly to self-antigens are:

  • Removed = central tolerance

  • Rendered non-responsive = peripheral tolerance

• Anergy = inactivation of self-reactive T cells

• Regulatory T cells = suppress activity of other T cells

• Clinal deletion = eliminate self-reactive lymphocytes in the periphery