2.4-Cell recognition and the immune system Flashcards
What is an antigen?
- Cell-surface molecule which stimulates the immune response.
- Usually (glyco)protein, sometimes (glyco)lipid or polysaccharide.
- Immune system recognises as ‘self’ or ‘non-self’ = enables indentification of cells from other organisms of sam speciec, pathogen, toxins & abnormal body cells.
How does phagocytosis destroy pathogens?
- Phagocyte moves towards pathogen via chemotaxis.
- Phagocyte engulfs pathogen via endocytosis to form a phagosome.
- Phagosome fuses with lysosome (phagolysosome).
- Lysozymes digest pathogen.
- Phagocyte absorbs the products from pathogen hydrolysis.
Explain the role of antigen-presenting cells (APCs).
- Macrophage displays antigen from pathogen on its surface (after hydrolysis in phagocytosis).
- Enhances recognition bu T(H) cells, which cannot directly interface with pathogens/ antigens in body fluid.
Give 2 differences between specific and nonspecific immune responses.
Nonspecific:
- immediate
- (inflammation, phagocytosis) = same for all pathogens
Specific:
- time lag
- (B & T lymphocytes) = complementary pathogen
Name the 2 types of specific immune response.
- Cell-mediated
- Humorol
Ouline the process of the cell-mediated response.
- Complementary T(H) lymphocytes bind to foreign antigen on APC.
- Release cytokines that stimulate:
a. clonal expansion of complementary T(H) cells (rapid mitosis): become memory cells or trigger humoral response.
b. clonal expansion of cytotoxic T cells (Tc): secrete enzyme perforin to destroy infected cells.
Outline the process of the humoral response.
- Complementary T(H) lymphocytes bind to foeign antigen on antigen-presenting T cells.
- Release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes.
- B cells differentiate into plasma cells.
- Plasma cells secrete antibodies with complementary variable region to antigen.
What is an antibody?
- Proteins secreted by plasma cells.
- Quaternary structure: 2 ‘light chains’ held together by disulfide bridges, 2 longer ‘heavy chains’.
- Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen.
- The rest of the molecule is known as the constant region.
How do antibodies lead to destruction of a pathogen?
Formation of antigen-antibody complex results in agglutination, which enhances phagocytosis.
What are monoclonal antibodies?
Antibodies producd from a single clone of B cells.
What are memory cells?
- Specialised T(H)/ B cells produced from primary immune response.
- Remain in low levels in the blood.
- Can divide very rapidly by mitosis if organism encounters the same pathogen.
Contrast the primary and secondary immune response.
Secondary response:
- Faster rate of antibody production.
- Shorter time lag between exposure and antibody production.
- Higher concentration of antibodies.
- Antibody level remains higher after the secondary response.
- Pathogen usually destroyed before any symptoms.
What causes antigen variability?
- Random genetic mutation changes DNA base sequence.
- Results in different sequence of codons on mRNA.
- Different primary structure of antigen = H-bonds, ionic bonds & disulfide bridges form in different places in tertiary structure.
- Different shape of antigen.
Explain how antigen variability affects the incidence of disease.
- Memory cells no longer complementary to antigen = individual not immune = can catch the disease more than once.
- Many varieties of a pathogen = difficult to develop vaccine containing all antigen types.
Compare passive and active immunity. Give examples of both types.
- Both involve antibodies
- Can both be natural or artificial
Passive natural: antibodies in breast milk/ across placenta
Passive artificial: anti-venom, needle sick injections
Active natural: humoral response to infection
Active artificial:vaccination
