Biology - Immunity

What is an antigen

Foreign protein that triggers immune respone

What is an antibody

A protein specific to an antigen, released by B cells

Outline phagocytosis

• pathogen recognized by phagocyte because it’s foreign

• pathogen is engulfed by endocytosis

• vesicle fuses with pathogen and then lysosome containing enzymes

• so the enzyme hydrolyses & destroys pathogen and then it is released via exocytosis

How does vaccination work?

• vaccine contains antigen from pathogen

• Macrophage presents antigen on its surface

• T helper cell with complementary receptor binds to antigen

• T helper cell stimulates B cells to undergo mitosis and secrete large amount of antibodies

Describe how B-lymphocytes respond when they are stimulated by antigens

• B lymphocyte engulfs antigen and becomes antigen presenting

• T helper cell with complementary receptor binds to antigen

• T helper cell stimulates B lymphocyte to undergo mitosis and make plasma cells which can secrete antibodies and memory cells which can differentiate into plasma cells and secrete antibodies upon re-exposure to pathogen

Suggest why it is advisable for people to be vaccinated against influenza every year

• Influenza mutates so its antigens change

• So influenza antibodies need replacing

Describe cell-meditated immunity

• T helper cell with complementary receptor binds to antigen on antigen presenting cell

• T cell clones by mitosis to:

• stimulate phagocytosis and mitosis of B cells, and activate cytotoxic T cells and become memory cells

How are monoclonal antibodies made ?

Why are they called monoclonal ?

• mouse injected with vaccine

• B cells are collected and fused with tumor cells

• forms hybridoma and then antibodies are collected

• Monoclonal → antibody made from single group of identical B cells

Give two ways pathogens might cause disease when they enter the body

• release toxins

• kill cells

Why are antibodies specific ?

It has specific primary structure meaning its tertiary structure is also specific so it is only complementary to one antigen

Describe the replication of HIV

• HIV’s attachment proteins bind to host helper T cell

• RNA & reverse transcriptase enters cell

• reverse transcriptase makes single complementary DNA strand from RNA

• Viral protein produced

• Virus assembled and released

Describe how HIV is replicated once inside helper T cells

1. RNA converted into DNA using reverse transcriptase

2. DNA inserted into T helper cell

3. DNA transcribed into mRNA

4. mRNA is translated into new viral proteins

What is herd immunity

Vaccinating a large amount of the population so most of the people are immune and the virus can’t spread

Difference between active and passive immunity

• Active is long term because antibodies are produced in response to antigen while passive is short term because antibodies given are broken down

• Active can take time to work while passive is fast acting

• Active involves memory cells while passive doesn’t

• Active involves antibodies from plasma cells while passive involves antibodies from outside source

how do cytotoxic t cells work

• kills abnormal or infected cells

• produces perforin which makes pores in cell surface membrane which kills cells

explain active immunity

memory cells differentiate into plasma cells rapidly to release lots of antibodies quickly upon exposure to same pathogen

describe and explain differences between primary and secondary response

• primary response releases less antibodies slower because it takes time to locate B cells with correct antigen

• secondary response is immediate and produces more antibodies faster because memory cells are roaming around ready for reinfection and differentiate quickly into plasma cells which release lots of antibodies rapidly upon second exposure to pathogen

describe the structure of an antibody antigen complex

• antibodies are flexible and so can bind to many antigens which help attract phagocytes so they destroy pathogens easier

• antibodies have different antigen binding sites because different primary structures create specific tertiary structures

how to identify non-self cells

• pathogen

• organ transplant

• toxins

• abnormal cells

what is AIDS

• viruses replicate in helper T cells and kill them

• immune system cant properly function since B cells cant be stimulated

• no antibodies produced

• person is vulnerable to infections

how does the pregancy ELISA test work

1. First mobile antibody, complementary to antigen being tested has colour dye attached to it

2. Second antibody, complementary to antigen is immobilised

3. Third antibody, complementary to first antibody is immobilised

ELISA test

1. Add first antibody complementary to antigen to base of beaker

2. Wash to remove unbound antibodies

3. Add second antibody, complementary to first, which contains enzyme

4. Wash to remove unbound antibodies

5. Add colourless substrate which produces coloured solution in presence of enzyme

6. Antigen is present if colour changes