Hr 2 immune response

CHAPTER 11 : IMMUNITY (5 hrs)

11.1 Immune Response (2½)

11.2 Development of Immunity (1½)

11.3 Immune Disorder ( 1 )

• Describe what is meant by immunity.• Describe the structure of antibody

and state the classes of antibodies.• Explain and compare humoral and cell

mediated immune response• Describe the roles of lymphoid organs

in immunity.• Describe various types of antigen and

antibody reactions.

11.1 : Immune Response (Objectives)

What is: Immunity ? Antigen ? Antibody ?

Structure of antibody

Classes of antibody

Immune response

Antigen & antibody reactions

11.1 : Immune Response

Immune response

Cell mediatedHumoral

Immune Response

Involve mainly B cell Produce antibody in

plasma (body fluid ~ humor)

With the help of TH cell

Involve mainly T cell

Our cells has a special glycoprotein on the plasma membrane MHC

Major Histocompatibility Complex (MHC)

MHC

Class I Class II

found on all cells (except RBC)

found on cells involved in immune response (macrophage, B cell)

Classes of T cells

Lymphocyte T

T4 / CD4 cell

Cytotoxic T cell (TC)

Suppressor T cell (TS)

T8 / CD8 cell

Helper T cell (TH)

a.k.a killer T cell

Has receptor forclass II MHC-Antigen complex

Has receptor for class I MHC-Antigen complex

Macrophage ingest & destroy the antigen by phagocytosis

Fragment of antigen is displayed on the cell surface together with a class II MHC

To form a class II MHC-antigen complex

These cells Antigen Presenting Cells (APC)

1. Humoral Immune Response

Antigen Presenting Cell

TH with a specific receptor bind to the complex Macrophage secrete Interleukin-1 (IL-1) Which activates TH to secrete Interleukin-2 (IL-2)

Which stimulate the activated TH to proliferate & differentiate to form 2 clones:-

Activated TH cloneMemory TH clone

1

2


Divide rapidly to form many TH which has identical MHC-antigen receptor (clone)

Proliferate

Differentiate Form different types of TH (activated TH &

memory TH)




When B lymphocyte binds to a specific antigen, it becomes activated (with the help of TH)

These activation causes B cells to proliferate & differentiate to form: Plasma / effector cells Memory B cells

Plasma cells secrete the same antibody that can bind to the invading antigen to form antibody-antigen complex

Antibody-antigen complex does not destroy the antigen but only prepare them for further process


Effective to protect against free antigen found outside the host cells

Antigen receptor on B cell can only bind directly to antigen


Involve mainly T cell

Effective against antigen found inside the host cells, cancer cell & transplant

Receptor on T cell can bind to MHC-antigen complex

2. Cell Mediated Immune Response

Classes of T cells

Lymphocyte T

T4 / CD4 cell

Cytotoxic T cell (TC)

Suppressor T cell (TS)

T8 / CD8 cell

Helper T cell (TH)

a.k.a killer T cell

Has receptor forclass II MHC-Antigen complex

Has receptor for class I MHC-Antigen complex

Also involve macrophage & TH cell *refer humoral immune response


Antigen infect cells with class I MHC Fragment of antigen is displayed on the cell

surface together with class I MHC molecule Forming a class I MHC-antigen complex Tc with a specific receptor binds to the

complex on infected cell When activated TH secrete IL-2

Cell Mediated Immune Response


IL-2 stimulates TC to proliferate & differentiate to form 2 clones:-

Stimulate TC to release perforin Which form pores in the infected cell’s membrane Causes it to lyse Activated TC clone circulate & kill other infected cells


Activated TC cloneMemory TC clone

1

2



3 possibilities : Ingested by macrophage Infect cells (not involved in immune

response) Bind with B cell with a specific receptors


B & T cells has a unique receptor on the cell surface Receptors bind to a specific antigen Each cell has the same receptors can only bind to

the same epitope B cell recognize antigen & bind to antigen (antigen

receptor T cells cannot bind to free antigen T cell can only recognise & act on the processed

antigen displayed on APC

Lymphocytes

Humoral Immune Response

Engulf & destroy antigen by phagocytosis Display fragments of antigen & class II MHC Secrete IL-1 Which activates TH cell to secrete IL-2

Role of Macrophage

Bind with class II MHC – antigen complex Secrete IL-2 Which stimulates proliferation &

differentiation of : Itself (activated TH & memory TH)

TC (activated TC & memory TC) B cells (plasma cell & memory B cell)

Role of TH cell

Bind to free antigen With the presence of IL-2, B cell proliferate

& differentiate into Plasma cell : secrete antibody Memory B cell

Role of B cell

Display fragments of antigen & class I MHC To warn other cells, intruder is present

Role of infected cell

Bind to class I MHC – antigen complex With the presence of IL-2, TC cell proliferate

& differentiate into Activated TC cell : secrete perforin to lyse

antigen Memory TC cell

Role of TC cell

Regulatory cell Release lymphokine That suppress / slow down the activity of B

& T cells When antigen has been successfully

destroyed Important to prevent unnecessary immune

response Help prevent autoimmune reaction

Role of TS cell

If exposed to the same antigen:- Proliferate faster to form clone Differentiate faster to form activated cells &

memory cells

Role of memory cell (all types)

Antibody binds to antigen to form Antigen-antibody complex

Antigen-Antibody Interaction

Antigen-antibody Interaction

NeutralizationAgglutinationPrecipitationComplement fixation

Simplest mechanism Virus / bacterial toxin have receptors that is

needed to infect our cells Antibodies block these receptors cannot

infect our cell ~ inactive Antibody is called antitoxin

Neutralization

Antibody : usually involves Ig M Antigen : foreign cell Ig M is large can bind to many antigen at

a time Form cross-linkage to form a large complex

clump This process is called agglutination Antibody is called aglutinin Basic test for blood typing Antibody bounded to antigen ~ stimulate

macrophage to conduct phagocytosis

Agglutination

Antigen : soluble (in form of molecules, not cell)

Antibody bind to antigen Form cross-linkage to form large complex

become insoluble & settle out of the solution (precipitate)

Antibody is called precipitin

Precipitation

Antibodies bind to antigen antigen-antibody complex

Stimulate plasma protein (complement) to bind to the antigen-antibody complex

Complement protein form a membrane attack complex (MAC)

Causing formation of pore on the target cell’s membrane

Cell lyse Antibody is called lysin

Complement Fixation

Complement Fixation

Antigen-Antibody Interaction

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Hr 2 immune response