Infectious DiseasesUnit 5 Lesson 3 plan

Do now

• Why might the innate response be unable to control an infection?

• What happens then?

Do now

• Why might the innate response be unable to control an infection?

• What happens then?

• What is ADAPTIVE IMMUNITY?

Do now• What is adaptive immunity?• What happens when innate responses don’t

control the infection?

B lymphocytes are made in the blood– Secrete antibodies

T lymphocytes are made in the thymus– Some help activate immune system responses.– Others attack and kill cells infected with

bacteria or viruses.

Adaptive immune cells are called

Lymphocytes.

• Antigens are:– Not usually found in the host – they are specific to the

pathogen.– They are recognized by a specific receptors on B and T

cells.

The T cell receptor binds antigen that is presented by an innate cell

Adaptive cells ‘see’ Antigens

The B cell receptor can be attached to the cell surface …

….or released from the cell surface as an antibody.

Small group brainstorming:

• At your table, take 10 minutes to complete the worksheet.

Each B and T cell responds to only one antigen

– There are millions of kinds of B cells and T cells

– Each randomly makes one antigen receptor.– They wait in the lymphatic system.– If they ‘see’ their antigen they will respond.

Only the B cells that ‘see’ their antigen respond!

Antigen

How do B cells recognize ‘their’ antigen?

• B cells bind to extracellular antigen.• They cannot ‘see’ an antigen that is inside cells!

• T cells only bind to antigen when it is presented to them by an antigen presenting host cell

• T cells can ‘see’ both extracellular and intracellular antigens!

Extracellular antigen (bacterial infection)

How do T cells recognize ‘their’ antigen?

• T cells only bind to antigen when it is presented to them by an antigen presenting host cell

• T cells can ‘see’ both extracellular and intracellular antigens!

Intracellular antigen (viral infection!)

How do T cells recognize ‘their’ antigen?

How do B and T cells respond?

At your table, discuss the following question:

– Each B and T cell receptor is unique because it was made randomly.

– So, if only one B cell has a receptor that recognizes H1N1, how could this lone cell control the infection?

1. B cells with antigen receptors

2. Bind to a specific antigen

3. Then begin to replicate – clonal expansion increases the pool of B cells available.

Remember, only the antigen specific cells respond.This creates a pool of adaptive recognition specialists!

As soon as B and T cells bind an antigen they begin to replicate – this is called clonal expansion!

Clonal expansion

Homework

• Write one paragraph that summarizes the main points of today’s lesson.