The Second Line of Defence Expected Learning: to investigate the second line of defence of immunity, including phagocytes, natural killer cells, inflammation and complement proteins.

Second Line of Defence o As mentioned in Eden and Theresa’s presentation, the body has a first line of defence against infection o If this fails, a second line of defence must take place in the body o The following are a number of way in which the body’s second line of defence takes action against disease and infection

Phagocytes  Phagocytes are white blood cells that engulf and destroy micro- organisms and other foreign material  They are produced in the bone marrow  They include neutrophils (most common white blood cell) and monocytes (largest white blood cell)  Bacteria and other microorganisms engulfed by phagocytes are broken down by enzymes and other factors released into the vacuoles containing the foreign material, and the bacterium is killed.

Natural killer cells  Type of white blood cell that kills virus-infected body cells  Most aggressive of all the white blood cells  Important in the fight against cancer  In the picture, the natural killer cell is the purple cell, attacking the foreign green cell

Complement Proteins  About 20 different complement proteins circulate in the blood  They work in different ways: -Stimulating phagocytes to become more active -Coating microorganisms so that they are more easily identified by phagocytes -Lysing (break open) bacterial membranes -Attracting phagocytes to the site of infection  Can help with specific immune responses (that we will learn later on) Page 248 of textbook

Interferon o Group of proteins o Secreted by some cells when they are infected by virus particles o Act on uninfected cells to make then more resistant to the virus o If a person develops a cold or flu, interferon has failed to prevent infection

Cytokines  Protein molecules that act as messengers between cells.  Produced by virtually all cells of the immune system  Communicate with cells in other body systems, including the nervous system  A cell can only respond to a message from a cytokine if it has an appropriate receptor.

Inflammation  Inflammation increases the blood supply to a site of infection, thereby increasing the number of white blood cells at the site  Caused by a number of plasma enzyme systems such as serotonin  Serotonin increases dilation of arterioles and permeability of vascular tissue (allowing more blood cells to pass through)  Phagocytes are carried to the area  The used up white blood cells that have already engulfed bacteria are stored in the form of pus in the infected area  Skin eventually repairs as infection disappears, reducing inflammation over time

Page 249 of textbook

Past Exam Questions

Answers

Reflection and Homework  What have you learnt about the second line of defence against infection?  How do complement proteins assist phagocytes?  What is pus?  Quick check  Biochallange 1