C12 - Immunity Flashcards
What are the three examples of non-specific immunity?
Barriers
Inflammation
Phagocytosis
These are the primary responses
What are the two examples of specific immunity?
Cell-mediated response using T lymphocytes
Humoral response using antibodies
What are the barriers for the body’s non-specific response?
Skin - the outer layer has keratin (insoluble protein) which prevents the entry of pathogens. Clotting occurs if the skin is broken
Conjunctiva (membrane covering eye) - thin layer protected by secreted lysozyme from tear ducts. This digests the bacterial cell walls, destroying bacteria
Ciliated epithelial cells in airways, further protected by the mucus it secretes - the ciliated cells waft the mucus and any trapped particles and pathogens out of airways and to the throat where it’s swallowed
Stomach lining - also has mucus layer and glands secreting HCl acid which can destroy pathogens
Vaginal lining - protected by mucus and acidic pH
What occurs during the inflammatory response?
Pathogens cause damage, resulting in local mast cells to release compounds such as histamine, serotonin and prostaglandins.
This causes the arterioles to dilate which causes the capillaries to become more permeable, so phagocytic white blood cells can leave the blood more easily.
Blood flow to the area is also increased, causing pain sensitivity.
This causes soreness, swelling and redness.
What are neutrophils?
Phagocytic (white blood) cells effective against microorganisms used in phagocytosis.
What occurs during phagocytosis?
1) Pathogens release chemicals, causing damage to cells. This results in them releasing cytokines which attracts phagocytes.
2) The pathogen becomes attached to the receptors on the cell surface membrane of the phagocyte either directly or by linking molecules.
Some of these molecules (opsonins) are produced as antibodies by other white blood cells while others (complement) are naturally found in blood plasma
3) The phagocytes surround the pathogen with a vesicle called a phagosome.
4) Lysosomes containing hydrolytic enzymes (e.g. lysozyme) fuse with the phagosome. The enzymes digest and destroy the bacteria within the vesicle. Harmless nutrients are released into the cytoplasm and useful nutrients are absorbed into the cell.
What are monocytes?
White blood cells that differentiate to form macrophages. These are large phagocytic cells found in tissues.
They release more chemicals that attack the bacterial cells, inhibit viral replication and attract more macrophages.
They engulf and destroy pathogens as well as damaged cells that are undergoing apoptosis.
What does the specific immune system do?
Target specific pathogens invading the body. The response to one pathogen will therefore result in different protection to that of another pathogen.
What triggers the specific immune response?
Antigens on the outer surface of organisms.
They can be identified as foreign ‘non-self’ antigens and cells belonging to the body / ‘self’ antigens.
These non-self cells are targeted and destroyed using phagocytes.
Where are T and B lymphocytes produced and matured?
B lymphocytes form and mature in bone marrow.
T lymphocytes form in the bone marrow but mature in the thymus.
What is the role and action of T lymphocytes?
Dendritic cells (type of macrophage) engulf and digest the pathogen and display the pathogen’s antigens on their cell surface membrane, becoming an ‘antigen presenting cell’.
Circulating dendritic cells eventually locate T helper cells. The macrophage activates the T helper cells and causes them to multiply by mitosis and differentiate.
They can differentiate to form T memory cells, cytotoxic / T killer cells, T regulatory cells etc.
How are specific B lymphocytes stimulated?
By cytokines produced by T helper cells.
Cytokines also stimulate phagocytic cells to engulf pathogens.
What is the role and action of B lymphocytes?
They have receptors that are complementary to the antigens on the pathogen.
The selected B cells divide rapidly and repeatedly by mitosis.
They differentiate to form plasma cells which synthesise to secrete antibodies with a complementary binding site to the pathogen’s antigens.
Some form B memory cells which provide immunological immunity.
What is clonal selection and clonal expansion?
The selection and multiplication of specific T and B lymphocytes.
What do cytotoxic / T killer cells do?
They destroy any cells infected by the pathogen by producing a protein which makes holes in the cell’s surface membrane.
The holes ensure the cell is completely permeable, causing the cell to die.
What do T regulatory cells do?
A.k.a. T suppressor cells, they regulate the immune system by maintaining tolerance to self antigens to prevent autoimmune diseases and suppress other T cells, especially after the elimination of invading organisms.
Why are memory cells important?
For long term immunity.
Antigen presentation will be quicker due to the existence of specific T and B lymphocytes so clonal selection and expansion would be much faster since B memory cells produce plasma cells.
