Specific Immunity Destroy specific antigens that invade the body.

Specific Immunity

Destroy specific antigens that invade the body

Specific Immune Responses

Take several days to activate

Have immunological memory

2 types: Cell-mediated immunity Antibody-mediated immunity

Meet the players…

MHC

APCs

Lymphocytes

Major Histocompatibility Complex

Group of closely linked genes – polymorphic

Distinguish self from non-self

Genes encode MHC antigens Differ in chemical structure, function and

tissue distribution

3 Types of MHC genes:

Class I – encode glycoproteins found on surface of most cells of body

Class II - glycoproteins expressed on APCs Combine with foreign antigens

Class III – secrete proteins involved in immune response

Complement system

Antigen-Presenting Cells (APCs)

Include: Macrophages Dendritic cells B cells

Inactive until their receptors recognize PAMPs on pathogen

Display foreign antigens + own on cell surface

APCs cont.

APCs ingest pathogen Break down most of it Remaining pieces of antigens displayed on

cell surface along with self-molecules

Signaling molecules are released

Present antigen to T cells

Lymphocytes

3 main types: Natural Killer Cells T cells B cells

All 3 develop from stem cells in bone marrow

Large #s of lymphocytes found in lymph organs

Memory

T cell

B

Lymphocytes, cont.

T cells Travel to site of infection Attack foreign cells & own infected cells

B cells Mature into plasma cells Plasma cells produce antibodies

T cells

Mature in the thymus gland Become immunocompetent Develop surface proteins w/ specific receptor

sites Must recognize self-antigens Must bind with foreign antigens If can’t distinguish between self & non-self,

undergo apoptosis http://www.bio.davidson.edu/courses/Immuno

logy/Flash/Main.html

Types of T cells

Cytotoxic T cells (TC cells) Recognize and destroy foreign antigens

including Grafts Virus-infected cells Cancer cells

Helper T cells (TH cells) Regulatory Secrete cytokines to activate B cells and

macrophages

Cell-Mediated Immunity

APCs

T cells

T cells

TC cells Have CD8 glycoproteins 50,000+ receptors that bind to 1 specific

antigen Recognize antigen-class I MHC complex

TH cells Recognize antigen-class II MHC complex

Less than 1 in 10,000 T cells have same antigen specificity

T cell activation

Cells must be activated before they can respond to pathogen

Activation requires: Properly presented antigen

Co-stimulatory signal Released by APC

Interleukin signal Released from macrophages and lymphocytes

After activation…

TC cells:

Enlarge and clone many TC cells specific for that antigen

Leave lymph nodes and go to infection

Combine with antigen and destroy cells within seconds

Secrete perforins and granzymes

Release and find new antigens to destroy

After activation, cont…

TH cells:

Clone

Release cytokines to attract macrophages and TC cells

Also play a role in antibody-mediated immunity

Both TC cells & TH cells produce memory cells for secondary immunity

Summing up Cell-Mediated Immunity:

Pathogen infects body cell

Cell breaks up pathogen and displays foreign antigen along with MHC-class I or II antigen on surface

Specific T cells activated and clone

TC cells leave lymph, go to infection, and destroy cell

TH cells release cytokines to stimulate TC cells and macrophages; also trigger antibody-mediated immunity

Antibody-Mediated Immunity

B cells

B cell activation

APC presents antigen to TH cell: Multiple chemical signals sent back & forth TH cell becomes activated **B cell can be an APC

Activated TH cell releases interleukins which, along with antigen, activates B cell

http://bcs.whfreeman.com/thelifewire/content/chp18/1802004.html

After activation…

B cell divides by mitosis Clone of identical cells Specific for the activating antigen

B cells mature into plasma cells Secrete specific antibodies

Plasma cells remain in lymph node but secrete antibodies into lymph/blood

Antibody (aka Immunoglobulin) Structure:

Types of Immunoglobulins:

5 classes of antibodies based on amino acid sequences

IgG 75% of human circulating antibodies Along with IgM, interacts with macrophages

and activates complement system Defend against blood pathogens – viruses,

bacteria, some fungi

Immunoglobulins,cont.

IgA – mucus, tears, saliva, breast milk Prevents bacteria and viruses from attaching to

epithelium Defends against inhaled or ingested pathogens

IgD Found on surface of B cells Helps activate B cells Aids in maturation of B cells

IgE Plays a role in allergic response Immune response to parasitic worms

How do antibodies work??

Highly specific

Binds to specific part of antigen Epitope

Activates processes that destroy antigen

Labels antigen for destruction, it doesn’t destroy antigen itself

Usu. Several antibodies bind with several antigens creating an antigen-antibody complex May inactivate pathogen or toxin

Prevent binding to host

Antigen-antibody complex stimulates phagocytosis

IgG and IgM antibodies work mainly through complement system Coat surface of pathogen to increase

phagocytosis Stimulate release of histamine Attracts phagocytes Complement proteins destroy the pathogen

Summing Up Specific Immunity

http://www.learner.org/channel/courses/biology/archive/animations/hires/a_hiv1_h.html

Memory

Responsible for long-term immunity Memory T cells Memory B cells

Primary immune response Occurs when 1st exposed to antigen Antibodies appear in 3-14 days After recognition, antibodies build up for

several days then decline

Secondary immune response Memory B cells persist for many years When exposed to antigen again, secondary

response is much more rapid Often don’t “get sick” because response is so

quick Booster shots given to trigger secondary

immune response

Active vs. Passive Immunity

Active – body develops after exposure to antigen Natural – pathogen enters naturally Artificial – pathogen introduced ex. vaccine

Passive – antibodies given; borrowed immunity Natural – mother to baby Artificial –injection with gamma globulin