L6 - Adaptive Immunity (B Cells)

Characteristics of the adaptive immune system

• Discrimination between self & non-self

• Specificity

• Adaptiveness

• Memory

Effector Functions of antibodies

• Neutralisation

• Precipitation

• Opsonisation

• Agglutination

• Complement fixation

Steps of Bone Marrow Development

1. Developing B-cells acquire functional B-cell receptors

2. B-cells whose Ig receptors bind to ‘self’ are eliminated

3. B cells leave bone marrow & move to secondary lymphoid tissue

4. B-cells come into contact with specific antigen

5. B-cells proliferate

6. B-cells differentiate

Clonal selection

Process by which specific B-cells that recognise an antigen are activated to proliferate and develop into memory or plasma cells.

Clonal expansion

Process by which activated B-cells rapidly proliferate to produce a large number of identical cells, enhancing the immune response against a specific antigen.

Clonal Deletion

Process by which B-cells that strongly recognise self-antigens are eliminated during development to prevent autoimmune reactions.

Surface Ig

Molecules expressed on the surface of B-cells that function as antigen receptors, allowing them to bind specific antigens and initiate an immune response.

Secreted Ig

Antibodies produced by activated B-cells that circulate in the serum and help neutralise pathogens by binding to specific antigens.

5 Classes of Immunoglobulin

1. IgM

2. IgD

3. IgG

4. IgA

5. IgE

Immunoglobulin Structure

Immunoglobulins are Y-shaped molecules composed of two heavy chains and two light chains, forming variable and constant regions that determine their antigen-binding specificity.

Fc

Crystallisable fragment at the stalk of the Y, which is composed of only the constant region of an immunoglobulin, responsible for interactions with immune cells and complement proteins.

Fab

Antigen-binding fragments that are composed of a constant & variable region, formed by the combination of one heavy chain and one light chain of an immunoglobulin.

Constant region

The part of an immunoglobulin that remains the same among different antibodies, providing structural support and mediating interactions with other immune cells.

Variable Regions

The part of an immunoglobulin that differs among antibodies, allowing for the specific binding to various antigens. It is formed by the combination of heavy and light chains.

Bonds connecting antibody together

Disulfide bonds

How many segments is the variable domain of the heavy chain?

3 segments - V, D, J.

How many segments is the variable domain of the light chain?

V, J.

IgM

The first antibody produced in response to an infection, characterized by a pentameric structure and important in early immune response.

IgG

Major class in the secondary response, activates complement and can cross the placenta

IgA

Antibody found in mucosal secretions with 4 antigen-binding sites

IgD

Antibody that is co-expressed in IgM that is rarely seen in a secreted form

IgE

Antibody associated with allergic reactions and defense against parasitic infections, binds to mast cells and basophils.

What type of antibody do all antibodies start at?

IgM