1. Cell mediated response What the B-cells miss or are not programmed to deal with T-cells are able to handle. Usually 1

2. 2 T Cells 80% of circulating lymphocytes. Much more complex structure. All T cells get “primed” to fight a certain antigen in the Thymus gland. Some of the types: – Regulatory T cells – Cytotoxic T cells – Memory Cells – Suppressor T cells

3. T Cell response How T-cells respond is similar to B-cells. – They identify the antigen – The correct T-cell goes through colonial selection and proliferation. – Then the correct T-cell performs it’s specific function (phaocytosis, chemical secretion, or signaling other cells) 3

4. Regulator T-Cells Once regulatory (helper) T-cells have bound with an antigen they stimulate proliferation of B cells and other Tcells. Without helper T-cells your body would not know to send out the killer Tcells nor what antigen to fight. 4

5. Cytotoxic T cells – Cytotoxic (killer) T cells: attack foreign cells or body cells infected by viruses (“cell-mediated immunity”). – They roam freely around the body looking for infected cells to chemically Kill. – They can be called to action in a certain area by helper T-cells. 5

6. Memory Cell Memory T cells: produced by the division of activated T cells following exposure to a particular antigen (remain on reserve, to be reactivated following Basically they remember the shape of a certain antigen and upon coming in contact know exactly which immune cell to call. 6

7. Suppressor T Cells Also a type of regulator cell, but this one releases the chemical signal that stops the production of B and T cells. 7

8. 8 Development of lymphocytes Originate in bone marrow from lymphoid stem cells B cells stay in bone marrow, hence “B” cells T cells mature in thymus, hence “T” cells These divide rapidly into families Each has surface receptors able to recognize one unique type of antigen= immunocompetence

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10. 10 The immune system protects organisms with layered defenses of increasing specificity Most simply, 1. physical barriers prevent pathogens such as bacteria and viruses from entering the body If a pathogen breaches these barriers, the 2. innate immune system provides an immediate, but non-specific response – Innate immune systems are found in all plants and animals If pathogens successfully evade the innate response, vertebrates possess a third layer of protection, the 3. adaptive immune system – Here, the immune system adapts its response during an infection to improve its recognition of the pathogen – This improved response is then retained after the pathogen has been eliminated, in the form of an immunological memory, and allows the adaptive immune system to mount faster and stronger attacks each time this pathogen is encountered