Introduction to Immune Responses

Question 1

Can you name some barriers in place to combat infection?

Answer 1

• Lysozyme, tears, nasal secretions, sebaceous gland secretions
• Mucus, saliva
• Cilia lining trachea
• Skin
• Sweat
• Cough
• Acid in stomach
• Commensal organisms in gut
• Spermine in sperm

Question 2

How do phagocytes kill?

Answer 2

• Microbe must attach to phagocyte
• Ingestion initiated
• Organism enters phagocyte in a vacuole
• Destroyed within vacuole
• Help needed
• Phagocytes don’t work alone
• Need help in attaching to + destroying organisms (mainly bacteria)
• Complement proteins help

Question 3

How does the complement system help?

Answer 3

• Group of proteins
• Task 1 - to help attachment of microorganisms + phagocytes
• They also act as an enzyme cascade system
• Enhance phagocytic function

Question 4

What do phagocytes do apart from kill?

Answer 4

• Produce chemotactic substances to attract other cells to site
• Increase vascular permeability - allow immune cells to get in

Question 5

Many immune cells make interferons. What do they do?

Answer 5

To interfere with viruses infecting other cells

Question 6

What cells are involved in the innate immune system?

Answer 6

• Natural killer cells
• Neutrophils
• Macrophages

Question 7

What cells are involved in the adaptive immune system?

Answer 7

• B lymphocytes
• T lymphocytes

Question 8

What are the primary lymphoid organs?

Answer 8

• Bone marrow (-> mature B cell)
• Thymus (-> mature T cell)

Question 9

What are the secondary lymphoid organs?

Answer 9

• Blood
• Spleen
• Lymph
• Lymph nodes

Question 10

Each cell has a slightly different cell-surface receptor for antigens, and hence binds to different antigen. How do B-lymphocytes and T-lymphocytes recognise antigens?

Answer 10

• B-lymphocytes recognise antigen through immunoglobulin receptors (antibody) on their surface
• T-lymphocytes recognise antigen through T-cell receptors

Question 11

When do lymphocytes start to proliferate in response to antigen?

Answer 11

• >10⁸ lymphocytes = >10⁸ diff specificities in your body
• the non-dividing cells live for years
• they patrol - wait to meet one (few) antigens their receptors bind to
• when/if their receptors bind to a complementary antigen, they proliferate

Question 12

How are virally infected cells lysed in comparison to bacteria?

Answer 12

• Virally-infected cells lysed by T-lymphocytes
• Bacteria lysed by antibodies

Question 13

What do B lymphocytes do?

Answer 13

• Make antibodies
• Immunoglobulins
• There are 2 types:
  
  • IgM - made first
  • IgG - made later

Question 14

How do antibodies work?

Answer 14

• Neutralisation
• Example - coat virus with antibody - stop it entering cells
• Opsonisation

Question 15

What is opsonization?

Answer 15

• Coat micro-organism with antibody
• Phagocytic cells have receptors for antibody
• Phagocytes can now attach to bacterium
• Engulf
• Kill
• This is team work!

Question 16

How do helper T cells work?

Answer 16

• T helper cells can’t see virus on their own
• So phagocytes phagocytose infectious agent
• They carry + present antigens to T helper cells
• When activated T helper cells release chemicals known as cytokines
• Cytokines encourage B cells to work
• Help B cells make antibody

Question 17

T cytotoxic cells can’t see viruses/bacteria on their own either. How do T cytotoxic cells kill?

Answer 17

• Cell becomes infected eg. virus
• Virus wants to replicate, makes proteins inside cell
• Cell cannot hide infection
• Virus proteins appear on cell surface - attached to a cell called a major histocompatibility antigen MHC
• T cytotoxic cells can see MHC + virus protein together
• Killing begins