Lecture 10 - Immunology - Adaptive Immunity

State the differences between innate and adaptive immunity

Adaptive immunity

* Antigen dependent
* Offers no immediate protection
* Has a slow response to a first encounter to antigens
* Exposure results in immunologic memory

State the two types of adaptive immunity

1. Antibody mediated immunity
2. Cell mediated immunity

State the function of B lymphocytes

Provide antibody mediated immunity

State the function of T lymphocytes

Provide cell mediated immunity

Describe what occurs during an antibody mediated immune response

* B cells develop into plasma cells which produce antibodies and immunoglobulins in the presence of specific antigen
* Antibody fits like a key into specific shape of antigent like a lock

Define immunoglobulins

Glycoproteins that are produced by plasma cells in response to specific antigens

Describe the function of immunoglobulins

* Neutralisation of antigen
* Immobilisation of bacteria
* Agglutination of antigen
* Activation of complement

Define antigens

Chemical substances that are recognised as foreign by the immune system

Describe the five principal classes antibodies are grouped into

1. IgG
2. IgA
3. IgM
4. IgD
5. IgE

Describe IgG

* 75% in serum
* Only class that crosses the placenta
* Fixes complement
* Neutralises toxins and viruses

Describe IgA

* Major class in secretions - tears, saliva and mucus
* Important in local immunity from toxins, viruses and bacteria
* Does not fix complement unless aggregated

Describe IgM

* First Ig made by foetus
* The first Ig to be made by virgin B cells when it is stimulated by antigen
* Good complement fixing
* Very efficient in leading to the lysis of microorganisms

Describe IgD

* Role in serum uncertain
* Found on B cell surfaces where it functions as a receptor for antigen
* Does not bind complement

Describe IgE

* Binds very tightly to Fc receptors on basophils and mast cells even before interacting with antigen - involved in allergic reactions
* Helps in killing parasites
* Does not fix complement

Describe how a cell mediated response begins

* Begins with activation of a small number of T cells by a specific antigen

Name the two classes T lymphocytes are divided into

1. Helper T cells - regulatory cells
2. Cytotoxic lymphocytes - destroy viral infected cells

Describe the role of T lymphocytes in cell mediated responses

* Helper T cells secrete cytokines which act as a costimulator for cytotoxic T cells and B cells
* B cells become activated and secrete antibodies in response to antigenic challenge
* Activate cytotoxic T cells eliminate microbes by releasing granzymes and perforins
* Helper T cells also stimulate the nonspecific immune response

Define primary response

Immune response that occurs as a result of the first exposure to an antigen

Define secondary response

›Immune response that occurs when the immune system is exposed to an antigen against which it has already produced a primary response

Define immunisation

Process by which a subject is rendered immune by deliberately introducing an antigen or antibody into the subject

Name a natural acquired immunity pathway

Active

* Antigens enter the body naturally, body produces antibodies and specialised lymphocytes

Passive

* Antibodies pass from mother to foetus via placenta or breastmilk

Name an artificially acquired immunity pathway

Active

* Antigens introduced in vaccines, produces antibodies and specialised lymphocytes

Passive

* Preformed antibodies in immune serum introduced into body by injection

How do defects in the immune system occur?

* Overactive immune response - hypersensitivity reactions
* Inappropriate reaction - autoimmunity
* Ineffective immune responses - immunodeficiency