Unit4 AOS1 - Bio

How pathogens can enter a body

ingestion, injection, inhalation

What initiates the adaptive immune system

the innate immune system through antigen-presenting cells such as dendritic cells or macrophages

Where are dendritic cells located

on and in epithelial tissues of skin and linings of gut and airways

two components of initiating immune response

phagocytosis, antigen presentation

Steps involved in antigen presentation and initiation of an immune response

The pathogen is engulfed into a phagosome, which fuses with a lysosome

The pathogen is digested by enzymes in the lysosome.

Some of the fragments (digested parts of an antigen) are released by exocytosis.

Some of the digested fragments of antigen (or peptides) are displayed on the MHC-II receptors on the surface of the macrophage or dendritic cell.

These dendritic cells/macrophages move to the lymph node and present them to naïve helper T cells that carry specific receptors for that antigen. (antigen presentation)

These helper T cells undergo expansion, clones are produced.

Helper T cells assist other immune cells by releasing specific cytokines (interleukins). These can initiate either the humoral adaptive immune system (stimulating the clonal selection/expansion of B cells) or the cell-mediated immune system (stimulating the clonal selection/expansion of cytotoxic T cells).

function of helper T cells

secrete cytokines that:

- activate cytotoxic T cells (to seek and destroy cells infected by viruses with a specific antigen)

- activate B cells (into becoming antibody-producing plasma cells to defend against pathogens carrying that antigen)

- activate macrophages (to remove antibody-coated pathogens by phagocytosis)

branches of adaptive immunity

cell mediated and humoral

acquired immunity

Immunity that is present only after exposure and is highly specific.

adaptive immunity

an immune response that is specific to a particular antigen and develops through contact with an antigen

allergen

an antigen that causes an allergic reaction

allergic response

rapid immune response to normally harmless antigens - e.g. dust/pollen. involves production of IgE antibodies by B lymphocytes and release of histamines by mast cells

Antibody

protein produced by plasma cells in response to antigens, react specifically with the antigen that induced their formation. immunoglobulins

antigen-binding sites

regions of an antibody molecule to which an antigen binds; also called variable regions

antigen-presenting cells

dendritic cells, macrophages, B cells. cells of the immune system that use MHC-II markers on their surface to present antigens to helper T cells to elicit an immune response

artificial active immunity

administration of disabled antigens to elicit the production of antibodies (fake but you put in the work)

artificial immunity

immunity formed through deliberate exposure and intervention

artificial passive immunity

the administration of antibodies to provide an immediate, specific immune response (fake but no work)

autoimmune diseases

diseases in which the immune system fails to identify 'self' material and makes antibodies against the body's own tissues

B lymphocytes/B cells

type of white blood cell that recognise antigens or pathogens and produce a large number of antibodies specific to an antigen - matures in the bone marrow.

How many antigen-binding sites do antibodies have?

At least 2 sites that must be identical on both sides of the antibody.

main structural regions of an antibody

Hinge region, variable region, and constant region.

function of hinge region

connects light and heavy chains of antibody

function of variable region

It forms the antigen-binding sites.

PIANO (antibody function)

Precipitation, Inflammation, Agglutination, Neutralisation of bacterial toxins/pathogens, Opsonisation

precipitation

antibodies bind to soluble antigens, causing them to become insoluble and precipitate out of solution

function of cytotoxic T cells

kill virus-infected cells with or without antibodies.

MHC full name

major histocompatibility complex

MHC

receptor proteins on the surface of cells that identify the cell as 'self'

MHC-I

- on all nucleated cells of the body

- presents antigens from inside the cell to determine whether the cell is infected or cancerous.

- if antigen is non-self, then the cell has been infected

- presents antigens to CD8+ cells.

MHC-II

- Only present on specific white blood cells (antigen presenting cells)

- Presents antigens that come from outside the cell.

- If antigens presented are non-self then there has been an infection.

Presents antigens to CD4+ T cells.