Protection against Disease + Genetics Flashcards
Non-specific defense mechanisms
Skin, mucus, cilia, saliva, commensal bacteria, tears.
Cilia
- Minute hairs on epithelial cells in upper parts of respiratory tract.
- Beat to create current which moves mucus and particles to throat. Swallowing carries microbes to stomach where they are killed. Coughing and sneezing removes trapped particles and microbes
Pharynx
Throat
Why skin is a good defense
Outer cornified layer of epidermis consists of dead, tough cells containing indigestible keratin providing resistance to bacterial invasion. Is dry and salty.
Secretions from sebaceous glands have antiseptic properties against certain bacteria.
Sebaceous glands
Associated with the hair follicle. Produce antiseptic sebum.
Commensal bacteria as a defense mechanism
Compete more successfully than pathogenic bacteria for nutrients on skin surface reducing no. of pathogens
Tears as a defense mechanism
Contain enzyme lysozyme.
Saliva as defense mechanism
Contains enzyme lysozyme. Chewing stimulates salivation increasing lysozyme in mouth.
Lysozyme as enzyme used in defense mechanisms
Breaks down bacterial cell walls
Mucus as defense mechanism
Secreted by epithelial cells lining the nasal passages and respiratory tract.
‘Sticky’ trapping bacteria and dust particles entering air passages.
Contains large amounts of lysozyme and other antibacterial substances
During phagocytosis, how does a phagosome form around the pathogen?
Phagocyte extends pseudopodia around microorganism and engulfs it forming a phagosome or phagocytic vesicle
B lymphocytes
Involved in humoral response, secrete immunoglobulins into plasma when exposed to the appropriate antigen, in order to destroy it.
Immunoglobulin
Specific antibody produced during humoral response in response to specific antigen.
Humoral response
antibody-mediated immunity
Immune response
Specific defence mechanism involving activation of lymphocytes against antigens which have entered the body.
T lymphocytes
Involved in cell-mediated immunity.
Mature in Thymus gland. Possess receptors which recognise specific antigens, bind to them and destroy them. Helper T cells + suppressor T cells help regulate antibody production by B cells.
Cell mediated immunity
Attacking pathogens and foreign tissues directly.
Antibody modes of action
- agglutination of antigens
- stimulation of phagocytosis
- precipitation of soluble toxins
- preventing pathogens attaching to cell membranes
Opsonins
Antibodies which label foreign cells for destruction by phagocytic white blood cells.
Precipitation
Antibodies attach to soluble toxin (antigen) molecules causing them to group together forming a precipitate. This neutralises action of toxins, destroying them.
Natural Active Immunity
Results from natural exposure to specific antigen, immunity develops following recovery from disease as memory B cells form.
Artificial Active Immunity
Vaccines contain antigens from a specific pathogen. Injection stimulates an immune response, B cells release specific antibodies against antigen. Some memory B and T cells form, providing protection against specific microorganism.
Booster
Follows vaccine, injection of same antigen is given at a later date to ensure a more effective response (secondary response) to produce long term, often life-long immunity
Natural Passive Immunity
Preformed antibodies are obtained across placenta and through breast milk. Provides short-term protection, as body is not stimulated into producing its own antibodies and memory B-cells.
Artificial Passive Immunity
Involves injection of preformed specific antibodies usually following exposure to particularly virulent antigens. Provides short-term protection.
Methods of reducing rejection of transplants
- Tissue typing - ensuring tissues of recipient and donor are genetically similar.
- Irradiation - of areas producing white blood cells, particularly bone marrow to reduce numbers of T-lymphocytes.
- Immunosuppressive drugs
What causes the differences in ABO blood groups?
The presence of agglutinogen on the surface of red blood cells, + the presence agglutinins in the plasma
Agglutinogen
Specific antigens present in cells which stimulate production of agglutinins in blood serum
Agglutinins
Antibody (immunoglobulins) that causes agglutination
What causes incompatibility to arise during blood transfusions?
Donor’s blood cells possesses specific antigens complimentary to the hosts antibodies resulting in agglutination.
Rhesus blood group
Classification determined by the presence of the Rhesus factor(antigen D) on the surface of red blood cell membranes. Rhesus positive individuals possess antigen D, but rhesus negative individuals do not.
What causes an individual produces rhesus antibodies?
If a rhesus negative individual comes into contact with rhesus positive blood, causing agglutination of the blood.
ELISA test
Enzyme linked immunosorbent assay - a method of measuring the amount of antigen/antibody in a sample. Involves using monoclonal antibodies, some w/ attached enzymes that catalyse easily detectable reactions.
How do haemolytic diseases of the newborn occur?
Rh- mother gives birth to Rh+ child. Rh+ blood cells enter maternal circulation at end of pregnancy (placenta becomes more permeable) or during birth. Mother develops Rh antibodies against antigens Rh+ antigens. 2nd pregnancy w/ Rh+ child results in agglutination of blood.
Monoclonal antibodies
Identical antibodies, w/ same tertiary structure. Have the same antigen binding site.
How are monoclonal antibodies produced?
Antibody-producing cells are made by fusing a specific B cell w/ a cancer cell. Hybrid cell divides to produce clones of cell, all producing the same specific antibody. By using different B cells to form the hybrid cell.
Uses of monoclonal antibodies
1) To target medication to specific cell types by attaching a therapeutic drug to an antibody.
2) For medical diagnosis - detect specific antigen/antibody.
Method for ELISA test
1) Test is performed in plastic tray containing wells, each coated w/ a specific monoclonal antibody. This is irreversibly bound to surface of well.
2) Fluid sample being tested is added to well. If complementary antigen is present, an antibody-antigen complex forms. Well is rinsed.
3) A second monoclonal antibody (specific for same antigen), w/ enzyme attached is added to well. 2nd antibody-antigen complex forms if 1st antigen binds.
4) Well washed again. Substrate for enzyme is added. If a colour forms, indicates complementary antigen was present.
Intensity of colour proportional to amount of antigen present.
Genotype
Genetic constitution of an organism. For a particular gene this refers to the alleles present.
Phenotype
Appearance of a characteristic due to the expression of the genotype and its interaction with the environment.
Alleles
Different forms of the same gene.
Locus
Position of a gene on a chromosome. Alleles occupy the same locus on each member of a pair of homologous chromosomes.
Codominance
Both alleles are expressed in the phenotype.
Multiple allelism
More than two alleles of a particular gene. However, only two alleles can be present in a genotype.
Sex-linked Gene
Gene is carried on one sex chromosome
Autosomal gene linkage
Genes are present on the same chromosome at different loci and as a result are usually inherited together.
Epistasis
When two or more genes contribute to a phenotype. The allele of one gene affects or masks the expression of another gene at another locus.
Main white blood cells involved in phagocytosis
Neutrophils
Macrophages
Cytotoxic T cells
Have surface receptors which allow identification and attachment to antigens. Secretes porphyrin to destroy pathogen.
Helper T cells
Stimulates B cells to divide and produce antibodies
Memory T cells
Remain in blood following infection and produce a quicker immune response upon reinfection.
