Section 2 5 cell recognition and the immune system

Used Uplearn, compared to textbook for this section

What are Lymphocytes?

• Form part of the specific immune response (involved in humoral and cell-mediated response)

• They identify: pathogens, toxins, cells from other humans and abnormal cells.

• They identify the non-self cells based on their antigen

• Each Lymphocyte has complementary receptors that bind to the antigen

What are antigens?

Proteins in the cell-surface membrane that trigger an immune response.

What are Phagocytes?

• Form part of the non-specific immune response

• They destroy pathogens via Phagocytosis

The steps of Phagocytosis

• The phagocyte is attracted to the chemicals released by pathogen, and moves along a concentration gradient.

• Receptors on the phagocyte binds to the pathogen

• Phagocyte engulfs the pathogen, to form a phagosome

• Lysosomes in the phagocyte fuse with the phagosome

• Lysozymes are released which hydrolyses the pathogen

• The phagocyte engulfs the soluble products of the pathogen and expels the rest.

The steps for Humoral immune response system

Primary response:

• When naive B cell’s receptor binds to the pathogen, it forms an antigen presenting cell.

• The antigen presenting B cell binds to a complementary helper T cell

• Stimulating the B cell to clone itself

• Where each clone differentiates into a plasma cell or a memory B cell

• The plasma cells release antibodies

Secondary response: Quicker, greater conc of antibody

• When memory B cell encounters the pathogen again, it will clone again to more plasma cells and more memory B cells more quickly

The differences between B cells and T cells:

• B cells mature in the bone marrow, T cells mature in the thymus

• B cells are involved in the humoral response, T cells are involved in cell-mediated response

What are antibodies and structure:

• Proteins produced by naive B cells in response to the presence of a specific antigen

• The shape of the antigen-binding site is as a result of antibodies tertiary structure.

What are monoclonal antibodies?

Antibodies with the same tertiary structure produced from cloned B cells

What is Agglutination?

• An antigen and antibody bind to form an antigen-antibody complex.

• Many monoclonal antibodies bind to the pathogens, which makes it easier for phagocyte to engulf.

The steps for Cell-mediated response:

• Naive helper T cells bind to antigen presenting cells

• Stimulating the helper T cell to clone

• Which helps B cells to clone in the humoral response

• Some help with cytotoxic T cells and phagocytosis

• Cytotoxic T cells bind to virus infected cells, and releases protein perferin (causes holes in the cell membrane) and leads to the cell’s death

Types of immunity: passive, active (natural and artificial)

• Passive immunity: Introduction of antibodies from outside source, no memory B cells formed (e.g. antibodies passed from mother, anti-venom)

Active immunity: production of antibodies by individual’s own immune system

• Natural active immunity: Results from individual becoming infected with disease naturally.

• Artificial active immunity: When an immune response is formed, but without suffering from symptoms of the disease.

Herd immunity

When large amount of population are vaccinated, making it difficult for pathogen to spread within that population.

The structure of HIV

• Attachment proteins bind to the receptors of host cell

• Capsid stores the genetic material

• Protective phospholipid layer, called lipid envelope

• Lipid envelope and capsid are connected by matrix

• Contains RNA strands and reverse transcriptase enzyme (important for HIV replication)

How HIV replicates?

• Attachment protein on HIV binds to the helper T cell.

• HIV protein capsid fuses with the helper T cells’ membrane

• Allowing viral RNA and enzymes to enter cells

• Reverse transcriptase converts RNA to DNA

• Viral DNA enters the nucleus and integrated into the hosts’ DNA

• Viral mRNA is formed (transcription)

• mRNA translated to form viral proteins

• Viral proteins are assembled to form a new HIV

How HIV effects immune system, and causes AIDS?

• HIV replication occurs from helper T cells, which are destroyed

• Helper T cells can not help clone B cells

• So, no memory cells are formed or Plasma cells

• So, no antibodies

• Also, no Cytotoxic T cells to destroy virus infected cells

The ELISA test

• HIV complementary antibody is fixed to the bottom of the reaction vessel

• The target antigen forms a complementary enzyme-substrate complex

• The vessel is washed for any unwanted pathogens

• Then a complementary antibody to the pathogen is added with an enzyme linked

• The vessel is washed for any unbound antibody

• The complementary substrate is added, if colour change then HIV (+). Else HIV (-)

Why antibiotics cannot be used on viruses, but on bacteria?

• Antibiotics disrupt cell wall synthesis and interfere with their metabolism

• But Viruses do not have a cell wall, and don’t have same metabolism pathways (rely on host cells)