April 6-7 th 2015. The specific defense system (aka immune system) recognizes and attacks specific pathogens. The immune system has 3 important characteristics:

Immune System April 6-7th 2015

The specific defense system

The specific defense system (aka immune system) recognizes and attacks specific pathogens.

The immune system has 3 important characteristics:» Antigen specific What is an antigen?

Antigens are molecules (usually sugars or proteins on cell surfaces) that incite an immune response



The immune system has 3 important characteristics:» Antigen specific » Systemic

What does systemic mean?Systemic means ‘whole body’. The specific immune system mounts an attack that circulates throughout the body, not just at the initial site of infection.



The immune system has 3 important characteristics:» Antigen specific » Systemic» Has memory

The body ‘remembers’ antigens that it has previously fought, and mounts an even stronger & faster attack if it encounters them again.

Cells (and chemicals) of the Immune System

» Lymphocytes• Natural killer cells function in non-specific defense* to kill virus

infected or cancerous body cells

• B-lymphocytes mature in bone marrow. They become activated by binding to specific antigens then divide to form:• Plasma cells which release antibodies• Memory cells which ‘remember’ specific antigens

• T – lymphocytes mature in the thymus. They become activated by binding to specific antigens then divide to form:• Cytotoxic (killer) T cells kill virus infected or cancerous body cells• Helper T cells stimulate the production of immune cells and release

chemicals which help destroy pathogens• Suppressor T cells stop activity of immune cells after infection is over• Memory T cells ‘remember’ specific antigens


» Lymphocyte quick review

• What do the B and T refer to? The place where the lymphocyte matures – the bone marrow or thymus.• Which cell has a similar function to

NK cells? How are these two cells different?

Cytotoxic T and NK cells both attack and kill virus-infected or cancerous body cells. They differ in that NK cells attack any abnormal cell, whereas cytotoxic Ts only attack cells displaying specific antigens.

Fill out the visual!


» Lymphocyte quick review

• Which cells directly attack pathogens?

None of these! • The NK and cytotoxic T cells

attack virus –filled cells.• The B cells produce

antibodies (which do directly attack pathogens)• The helper Ts produce

chemicals which will kill pathogens

Fill out the visual!


» Macrophages• Play a role in non-specific AND specific defense system

• Engulf foreign particles (non-specific system)• Act as antigen presenters (specific system) by displaying

fragments of these particles on their surface and activating T lymphocytes.


» Antibodies• Proteins produced by plasma cells (B cells) that bind to specific

antigens• Binding of antibodies to pathogen causes their destruction /

inactivation in one of a few ways• Complementation: Encourages other chemicals (complements)

to punch holes in the surface of the pathogen, destroying it. • Neutralization: Binding prevents viruses or toxins from entering

healthy body cells• Agglutination / Precipitation: clumping of antibody-bound

particles, which makes them unable to enter healthy cells and more likely to be eaten by phagocytes

• Increased phagocytosis – the presence of antibodies ‘flags’ a pathogen, increasing the chance that it will be eaten by a phagocyte.


» Other important chemicals• Complements – proteins in blood that bind to pathogens; activity

increased by presence of antibodies• Interferons – proteins that bind to virus-infected cells and reduce

the ability of viruses to multiply; also work with T cells to increase recognition of virus infected or cancerous cells.

• Histamines and kinins – cause inflammatory response• Lymphokines and monokines – released by T cells, increase

immune response and directly destroy pathogens

Fun FactInterferon therapy is used in combination with other treatments to fight many cancers and Hepatitis B and C.

Fun FactHistamines are involved in allergic response

You are responsible for knowing: complements, interferons, and histamines

Two Branches of Immune System

There are two branches of the immune system:

» The humoral immune response which involves the production of antibodies that fight extracellular pathogens (pathogens including viruses and bacteria that are among our cells, but not inside them).

» The cell-mediated immune response which involves the activation of cytotoxic T cells that destroy virus-infected body cells and cancer cells.

But, before we talk about these, I need to tell you about …

The story of the lucky lymphocyte

The body naturally produces a HUGE array of B- and T- lymphocytes, with widely diverging receptors. *

Each receptor is capable of binding with only one type of antigen.

These mature, but inactive, lymphocytes take up residence in lymphatic organs and wait to meet their antigen.

Most never will.

The lucky few lymphocytes that do bind to their antigen will undergo clonal selection so that they, and their multitude of offspring, can fulfill their destiny by participating in the humoral or cell-mediated immune response.

Humoral Immune Response

1. B-lymphocytes bind to specific, free-floating antigens and become activated.

2. The activated B-lymphocyte divides many many times, forming identical clones, also capable of binding to the antigen.

3. Most of these clones will become plasma cells that specialize in producing antibodies that bind only with that specific antigen.

4. A few will become long-lived memory cells that will persist for years, waiting in case the same antigen is encountered again.

Fun fact: A plasma cell can produce 200 antibodies each second!

Primary vs. Secondary Humoral Immune Response

» The primary humoral immune response occurs the first time the immune system encounters a specific antigen.

» The secondary humoral immune response occurs any time after the immune system first defeats an antigen. This response is much faster and produces more antibodies.

Why?It takes time because the matching B lymphocyte must find the antigen, and be activated before the clones can be made.

Why?Because the body already has many matching B memory cells, and these will divide to produce even more plasma cells than in the 1st response.

Primary vs. Secondary Humoral Immune Response

How does this graph explain the function of vaccines?

Secondary response is why you become ‘immune’ to diseases

Why are boosters necessary?

Types of acquired immunity

The least common method is artificial passive immunity. Used for exposures / disorders that are likely to be fatal before the body can mount its own immune defense.

Includes: antivenom, botulism, rabies, & tetanus

Types of acquired immunity

Will passive immunity protect a person in case of secondary exposure? Why or why not?

No, because the person will not have memory cells.

Cell-Mediated Immune Response

The humoral immune response involves the production of antibodies and memory B lymphocytes.

What does the cell-mediated immune response involve?The production of cytotoxic T lymphocytes

and memory T lymphocytes.


» T-cell activation• Like B-cells, T-cells must bind to their one, specific antigen before

they are activated.• Unlike B-cells, T-cells cannot bind to free-floating antigens and

must bind to an antigen-presenting cell, like a macrophage.

» Activated T cells will clone (multiply)» T cells will do their specific jobs


» Types of T cells• Cytotoxic Ts… do what?


» Types of T cells• Cytotoxic Ts kill virus infected or cancerous body cells by shooting

them with chemicals that destroy their cell membrane• Helper Ts have many jobs

• Encourage division of activated B cells and cytotoxic Ts• Encourage production of antibodies from plasma cells• Release chemicals (lymphokines) which attract white blood cells

and enhance activity of phagocytes• Suppressor Ts

• Release chemicals that inhibit B and T cells, to slow immune response once antigen is destroyed

• Memory Ts• Long-lived cells that remain for quick response upon

subsequent infectionWhy might helper Ts be thought of as the bridge between cell-mediated immunity and humoral immunity?

Closure

» What were our objectives, and what did you learn?

» How does this relate to our unit question?» What learner profile trait did we demonstrate,

and how did we show it?

Exit Ticket

1. The cells that produce antibodies are calleda. Macrophages b. Memory cellsc. Plasma cells d. Cytotoxic cells

2. The cells that stimulate the production of immune cells area. B-lymphocytes b. Helper Tsc. Cytotoxic Ts d. Macrophages

3. Which of the following is not part of the specific defense system?

a. Macrophages b. Antibodies c. Natural killer cells d. Plasma cells

Exit Ticket

4. Which bind directly to antigens, causing their destruction or inactivation?

a. Antibodies b. Natural killer cells c. Helper Ts d. Cytotoxic Ts

5. Antibodies that pass from mother to infant through breast milk are an example of which type of immunity?

a. Passive natural b. Active naturalc. Passive artificial d. Active artifical

6. Vaccines are an example of which type of immunity? a. Passive natural b. Active naturalc. Passive artificial d. Active artifical

Exit Ticket

7. Which of the following does not bind to specific antigens? a. Antibodies b. Macrophages c. Memory cells d. T cells

8. Which type of immunity does not protect against future exposure to the same antigen?

a. Active immunity b. artificial immunity c. Natural immunity d. Passive immunity

9. The repeated division of a specific immune cell and its progeny is calleda. Activation b. Cloningc. Neutralization d. Agglutination

Exit Ticket

10. Which type of cell frequently serves as an antigen presenting cell?

a. Antibody b. macrophagec. Cytotoxic T d. Plasma cell

Extra Credit 1 (2 pts):What is the primary difference between humoral and cell-mediated immunity?

Extra Credit 2 (2 pts)Compared to primary humoral immunity, secondary humoral immunity occurs more ___________ and produces more ________________.

Documents

April 6-7 th 2015. The specific defense system (aka immune system) recognizes and attacks specific pathogens. The immune system has 3 important characteristics: