Announcements

• Chapter 14 Part 2 homework due today by end of class

• Today you received back your group project comments-between now and Thursday share with group members

• By Thursday sign-up for a time to meet with me in lab as a group about your project

• Chapter 15 Part 1 homework due on Wednesday

Ch. 15 Part 1Adaptive Immune Response

Where We Left Off…

You stepped on a nail, how do cells of the innate immune system know how to go to your foot

rather than your head?

Answer: They have different types of receptors on their membranes that allow them to 1)

detect various stimuli and 2) respond to it by chemoattractant gradients.

Well there’s a problem…

Remember, you stepped on the nail and the innate immune cells (PMNs, Macrophages, Monocytes,

Dendritic Cells) came to your rescue but the infection gets worse INSTEAD of better…

NOW WHAT??

Your adaptive immune response kicks in! But, by now it has been a couple of days…remember it’s a delayed response because it relies on the innate response first!

Question

How does the innate response help start the adaptive response?

Answer: The innate cell called dendritic cells are the link for T cell (an adaptive immune cell type)

activation.

Dendritic Cells Are Critical To Activate or “Turn On” T Cells (Cell-Mediated). B Cells (Humoral) Activate Themselves But

Rely On T Cells For Help.

Question

Where are dendritic cells located in the nail example?

Answer: In the foot

Why? They need to pick up antigens.

Let’s Talk Antigens…

• Dendritic cells and B cells pick them up, while T cells can only respond to antigens that have been presented and degraded by dendritic cells and B cells

• What are they? Antigens are molecules that react with a receptors on immune cells.

• They include a variety of materials such as invading microbes and their products

• 2 general categories:– T cell dependent: B cells responding require T cell help

• ***MOST ANTIGENS ARE THIS***

– T cell independent: B cells responding do NOT require T cell help

Did you know…

Naïve (unactivated, never seen infection) T cells reside in the lymph nodes.

So, how do dendritic cells get to the T cells?

Lymph Node And Lymphatic System: Your Highway for

Immune Cells

For the foot example, what lymph node do the dendritic cells traffic to?

Your throat?

Everyone’s In the Lymph Node, Now How Do T Cells Become Activated?

• T cells see antigens that dendritic cells picked up in the foot

• A specific interaction• Example: T cell specific for flu

only sees flu antigen to be activated. A T cell specific for the cold virus cannot become activated by flu antigen

• There’s two different types of T cells and they see antigens differently…

T-cell receptor(TCR)

Antigen-bindingsite

CD marker

Antigen

MHC Class I and II Antigen Recognition• MHC-Major

Histocompatibility Complex

• Way to present antigens by degrading them

• Looks like a bun (MHC) with a hot dog (degraded antigen)

• CD8 T cells see MHC class I

• CD4 T cells see MHC class II

3 Signals for Full T Cell Activation

• Signal 1: TCR:Antigen Signal presented by MHC

• Signal 2: Costimulatory molecules to help enhance the signal

• Signal 3: Cytokines to help polarize the cell to one type over another

Wait…What About the B Cells? Where are they? How do they become activated?

• Naïve B cells constantly use the lymph highway and recirculate to body to find antigens.

• Where would they find the antigen in the nail example?– The Foot!

• Then what? They traffic back to the lymph node closest to the infection. (Knee for nail example)

• Why? Some need help from T cells to become fully functional/activated

How B Cells Become Activated to T Cell Dependent Antigens

How B Cells Become Activated to T Cell Independent Antigens

• Leads to full activation due to multiple receptors engaged

Question To Think About…

Your B and T cells are now activated in response to the foot infection. Now what? How do they get back to the site of infection? What do they

produce?