L3: Adaptive Immunity and B cells

Adaptive Immunity

slower, antigen specific - specific for a certain disease

What are the features of adaptive immunity?

Specificity, Versatility, Memory, Tolerance

Specificity

activated by and responds to a specific antigen

Versatility

ready to confront any antigen at anytime

Memory

“remembers” any antigen it has encountered

Tolerance

responds to foreign substances but ignores normal tissues

How is specificity achieved?

Both B and T cells have receptors that recognize specific shapes

How is versatility achieved?

Different B and T cells have different receptors

How is memory achieved?

Some activated B and T cells are long lasting

How is tolerance achieved?

B and T cells with receptors that recognize self are deleted or not activated

(1) Specificity & (2) versatility of B and T cell receptors

Antibody

Immunoglobulin

• a Y-shaped protein made by the immune system (specifically plasma cells) to identify and neutralize foreign invaders like bacteria, viruses, and toxins (antigens)

B cell receptors bind to _______ ______

extracellular antigens

T cell receptors bind to ________

antigens displayed on the surface of cells

• (macrophages, tissue cells, etc)

T and B cells circulate throughout the body _____ __ _____

searching for antigen

Where are antigens encountered?

secondary lymphoid tissues - lymph nodes or spleen

Clonal selection, expansion and memory

Primary and Secondary Immune Responses i.e. (3) Memory

B and T lymphocytes originate in the bone marrow Need to be educated i.e. (4) Tolerance

Need mechanism to eliminate the ones that have the potential to attack our own body strongly

T cells undergo positive and negative selection in the _____

thymus

B cells undergo positive and negative selection in the

Bone marrow

negative selection

if there are B or T cell receptors that recognize self proteins — those are deleted

Positive selection in T cells

seeing MHC molecules

Antibody structure

B cells make ______

antibodies

Every human has between __________

10⁷ and 10⁹ different shaped Fabs

How are B cells activated?

1. Antigen binds to specific B cell via B cell receptors

2. Antigen is internalized, digested and combined with MHC and then transported to cell surface

3. Specific helper T cell recognizes antigen and MHC becomes activated and secretes cytokines

4. Activated B cell divides. Some daughter cells become plasma cells and secrete antibodies, others become memory B cells

Antibody Functions

1. Antigen clumping

2. Inactivation of bacterial toxins

3. Act as opsonins to tag antigens for phagocytosis

4. Trigger degranulation

5. Activate Complement

6. Activate B lymphocytes

Inactivation of bacterial toxins

prevents toxin from binding to a cell

Antigen clumping

creates bigger structure so it is more likely to be engulfed by phagocytes

Classes of antibodies

IgG, IgM, IgA, IgE, IgD

IgG

Most common type of circulating antibody - Transferred across the placenta from mother to baby

IgM

First type of antibody to be secreted in response to a new antigen

• Good at causing antigen clumping and activating complement

IgA

Crosses epithelial cells. Protects epithelial surfaces and present in breast milk

IgE

Fights parasites. Eosinophils have receptors for the IgE. Release histamine. Associated with allergic reactions

IgD

Are the B cell receptors on the surface of B cells

Types of adaptive immunity

Active and Passive

Active Adaptive Immunity

Exposure to a pathogen. Long lasting generates memory B and T cells

Passive Adaptive Immunity

Transfer of Ab from another organism. Lasts about 3 months because Ab degraded

Types of adaptive immunity diagram

Coordination of innate and specific immune system: response to extracellular bacteria

Summary

• Features of adaptive immunity: Specific, versatile, has memory, tolerant to self

• Features achieved by T and B cells having different receptors with different specificities, the generation of memory cells and deletion or inactivation of T and B cells that react to self

• B cells are activated through binding to antigen to B cell receptors, presentation on MHC class II, activation of specific helper T cells, generation of plasma cells that secrete Ab

• Antibodies protect us by binding to antigen blocking the action of the antigen and further activating the immune system