Download Specific Responses

Specific Responses
All sorts of fun stuff
What is this anyway?
• Non-Specific defense has failed to stop the infection
• Against particular pathogens
• Exhibit memory
Let’s get to know the bad guys: Antigens
• A particular molecule, usually part of a pathogen or cancer cell
• Also foreign antigens, those that the body does not produce
• As well, self-antigens, which are those made by the body itself
The process
• We know our opponents, but how do we emerge victorious?
• The first step is recognition
• A particular antigen is recognized
• Then comes the response
• Takes 5-7 days to mount a response
• More on this later
• And then, we remember
• The immune system remembers the antigens that it has previously seen
• Reaction time significantly decreases the next time
Microscopic guardian angels: Lymphocytes
• Two types:
• B Cells
• T Cells
• Both manufactured in red bone marrow
• B cells mature in red bone marrow
• T cells mature in the thymus
How do they battle infections?
• Each has a specific antigen receptor
• B-cell receptor for B-cells
• T-cell receptor for B-cells
• Each has receptors that only combine with one type of antigen
• Kind of like a lock and key mechanism
• There exist specific B and T cells for any possible antigen we are
likely to encounter during our lifetime!
B-cells
• They do antibody-mediated immunity
• When they encounter an antigen, the receptor immediately recognizes it
• B-cell gives rise to plasma cells
• These produce specific antibodies
• The antibodies have the same specificity as the B-Cell Receptor
• The progeny (descendants) of the B-Cell that was activated
become memory B-cells, and can recall that particular illness
T-Cells
• They do cell-mediated immunity
• Do not immediately recognize an antigen directly
• Must be brought to them by an antigen-presenting cell
• Exist primarily as:
• Helper T-Cells
• Regulate specific immunity
• Cytotoxic T-Cells
• Take care of cancer cells and viral cells
• Some also become memory T-Cells
• Defend against the same virus or a same type of cancer
The Clonal Selection Model
• What happens when a B-Cell Receptor combines with an antigen?
• Only the BCR that combines with the specific antigen clone will go
on to divide and produce many new cells
• Called antibody-mediated because most clones become the
plasma cells that produce the specific antibodies
• Also called humoral immunity
• Antibodies are present in blood and lymph
• Some progeny of the activated cells become B memory cells
• When the infection has passed, plasma development halts
Active and Passive Immunity
• Active Immunity
• An individual produces a supply of antibodies
• Body produces antibodies as a result of infection, infection is stopped
• Can be brought on by Immunization
• Use of vaccination to expand cloning of B and T Cells
• Most often are the pathogens themselves
• Passive Immunity
• Antibiotics are prepared for the individual to combat a disease
• Short-lived because not made by their plasma cells
• Breastfeeding promotes extended passive immunity after birth
Structure of Antibodies
• Y-shaped protein molecule with two arms
• Has a “heavy” (long) polypeptide chain
• Has a “light” (short) polypeptide chain
• Have a constant region, located at the trunk of the Y
• Variable regions form an antigen-binding site, specific to a specific antigen
• Antibodies also called immunoglobulin (Ig)
• Most typical is IgG, a Y-shaped molecule
• These cross the placenta from a mother to a fetus
• Also IgM antibodies, w2hich are pentamers
• Five Y-shaped molecules
Antigen-Antibody Combat
Antigen-Antibody Combat
• Several different ways
• If antigens are part of a pathogen, antibodies may completely cover them
• Called Neutralization
• This reaction leaves a mixed clump of antigens and antibodies
• Called an immune complex
• These antibodies attract white blood cells that move in and finish the job