Lesson 2: Adaptive Immunity Flashcards
(12 cards)
Adaptive Immunity
There are parasites, viruses and diseases that the body cannot deal with using non-specific methods
Also called acquired immunity, it is only found in vertebrates.
Adaptive immunity is different for every individual as it is based on previous pathogen exposure
Lymphocytes
Lymphocytes are the cells responsible for adaptive immunity.
There are two types of lymphocytes produced in the bone marrow; B lymphocytes (B cells) and T lymphocytes (T cells)
The immune system uses 2 specific defense mechanisms:
Cell Mediated Immune
Response – attacks infected cells
Humoral Immune Response –
attacks pathogens in the body
fluids
Clonal Selection
As B and T lymphocytes mature, certain genetic sequences are activated that
determine the antigen receptors that cell will display.
There are thousands of different antigen receptors and therefore types of B and T lymphocytes that are found in the lymph and lymphatic organs
When an antigen is present and detected by a lymphocyte, that lymphocyte becomes activated and begins the cloning process that produces thousands of genetically identical cells.
Clonal Selection of B Lymphocytes
An antigen binds with the antigen receptors on one B lymphocyte.
This lymphocytes is activated. It grows and divides into two genetically identical yet physically different types of cells.
One cell type becomes plasma cells that are short lived effector cells active in the primary immune response
The other becomes memory cells that initiate a secondary immune response
Primary Immune Response
Occurs upon first exposure to an antigen.
The cloned plasma cells secrete antibody molecules at a rate of about 2000 per second.
These antibodies circulate in the blood and lymph and are effective at combating the infection.
Each of these cells lasts only about 5 days before dying.
Secondary Immune Response
Occurs upon second exposure to an antigen.
When memory cells that were
produced during the primary
response are activated by a
second exposure to an antigen, clonal selection begins again.
This response is faster and
stronger than the first.
Humoral Immune Response
Bone marrow produces mature B lymphocytes which are stored and replicated in the lymph nodes.
B lymphocytes have receptors that bind to specific antigens.
Antigens (bacteria, fungi, viruses) stimulate the production of B lymphocytes
Eventually the antigen is detected by a B lymphocyte with a specific receptor that matches the antigen.
Activated lymphocytes begin clonal selection, to produce clones of identical cells.
Some of the cloned lymphocytes produce and release antibodies into the bloodstream.
Some of the cloned lymphocytes remain in the bloodstream as memory
cells, which provide protection against infection by the same antigen at a later date.
Antibodies
Antibodies are protein molecules produced in response to any antigen that
enters the body.
There are millions of antibodies and each is specific to an antigen
Fragments of pathogens or the presence of their toxins might also stimulate
antibody production.
Antibody Structure
Each antibody has a basic Y
shape.
It is the arrangement of
molecules at the top of the Y
that forms antigen specific
binding sites. This is what
makes each type of antibody
unique. The antigen binding sites attach to the corresponding antigen on the surface of the pathogen or its toxin.
Once an antibody has attached to an antigen it can destroy it in a number of
ways:
Agglutination – clumping together of pathogen
Neutralization of viruses and bacteria – prevent the entry of pathogens to cells
Neutralization of toxins – prevent cells from being affected by toxins
Opsonization – makes pathogens more recognizable to phagocytes
Activate complement system – the complement system is a collection of proteins that result in the rupture of the pathogen cell membrane
Cell Mediated Immune Response
T lymphocytes respond to antigens present on the cells of the body.
They undergo clonal selection and produce two types of effector cells; Cytotoxic T cells and Helper T cells.
Clonal selection also produces memory T cells which function like memory
B cells.
Helper T Cells
Helper T cells have many functions, including activating cytotoxic T cells and macrophages and stimulate B cells to produce antibodies.
Helper T cells function through their interaction with other white blood cells that are antigen-presenting cells (APCs)
Once activated, helper T cells function to activate other cells.
A typical APC is a macrophage. It will ingest a foreign particle and break it
into fragments.
A protein known as a self protein will bind with a foreign antigen (nonself
molecule) and be displayed on the surface of the macrophage as a self-nonself complex.
Helper T cells recognize and bind to this complex if the T cell contains the correct receptors.
The now activated helper T cell begins the secretion of a stimulatory protein known as interleukin-2. This protein does three things;
Cause the helper T cell to grow and divide to produce more cytotoxic T cells and memory cells.
Activate B cells to produce antibodies
Stimulates the activity of cytotoxic T cells
Cytotoxic T Cells
Cytotoxic T cells identify infected cells by detecting foreign antigens on those cells and binding with the self-nonself complex on the infected cell.
Binding activates the T cell to produce perforin which is a toxic protein that acts on the infected cell by making holes in it.
T cell enzymes can then enter the cell and cause apoptosis.
