Lecture 24 Flashcards
Define humoral immunity
Production of antibodies by B cells; circulating antigens are identified and targeted; the cells producing these antigens are then targeted for destruction by macrophages
Define cellular immunity
Depends on T cells and is directed against cells infected with a pathogen and expressing the pathogen’s protein, i.e. the antigen on the host cell surface
Explain antibody structure
Immunoglobulin molecule consisting of 4 polypeptide chains (2 light and 2 heavy chains) that combine to form a Y-shaped structure
Explain how antibody diversity is generated
It is produced by somatic recombination; genes encoding antibody segments are diverse and reshuffled to produce a variety of segmental combinations; diversity is increased by differing combinations of light and heavy chains, occasional deletions of nucleotides at the segment junctions, and high mutation rates in the immunoglobulin genes
What is the significance of the MHC?
Major function is to bind to peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T cells; in an organ transplant, you have to have a genetic match; the greater the mismatch, the stronger the immune rejection
What are some diseases of the immune system?
Graves disease (Hashimoto thyroiditis): thyroid gland
Rheumatic fever: heart muscle
Systemic lupus erythematosus: joints, skin, other organs
Rheumatoid arthritis: joints
Insulin-dependent diabetes mellitus: insulin-producing cells in pancreas
Multiple sclerosis: myelin sheath around nerve cells
What is the hygiene hypothesis and how is it used to explain increased asthma in wealthy nations?
Hypothesis: explains the increased prevalence of hay fever and eczema in families with small size and higher standards of cleanliness and studies have shown an inverse association between growing up on a farm and atopic diseases; wealthy nations tend to have smaller family sizes, live in urban homes, and use more antibiotics, leading to more disorders and allergies
Define an antigen
Molecules that elicit an immune reaction
Define an antibody
Proteins that bind to antigens and mark them for destruction by phagocytic cells
Explain the process of clonal selection
- In a large pool of lymphocytes each is specific for one antigen
- When an antigen binds to a B cell, the B cell divides and gives rise to a clone of B cells, all specific for the same antigen
- This proliferation of lymphocytes is the primary immune response
- Some cells differentiate into antibody-secreting plasma cells
- Antibodies are specific for the antigen
- Memory cells remain in circulation
- If a second exposure of the same antigen occurs, the antigen binds to the memory cells, which rapidly give rise to a secondary immune response
Define neutralisation
Neutralizing antibodies block parts of the surface of a bacterial cell or virion to render its attack ineffective
Define agglutination
Antibodies “glue together” foreign cells into clumps that are attractive targets for phagocytosis
Define precipitation
Antibodies “glue together” serum-soluble antigens, forcing them to precipitate out of solution in clumps that are attractive targets for phagocytosis
Define complement activation (fixation)
Antibodies that are latched onto a foreign cell encourage complement to attack it with a membrane attack complex, which leads to the following:
Lysis of the foreign cell; activating inflammatory processes by chemotactically attracting inflammatory cells
