Introduction to the immune system Flashcards
What is the function of the immune system?
1.Defend against invading microbes and injury/damage
1.Identify and destroy cancer cells that arise in body
3.Function as a “cleanup crew” that removes worn-out cells and tissue debris
Describe barrier immunity.
First line of defence.
3 types:
-Physical:
Skin, Epithelial lining, Commensal Bacteria
-Mechanical:
Tears, Mucus, Cilia, Rapid turnover of epithelial cells, Peristalsis
-Chemical:
Acid, antimicrobial enzymes (lysozymes breaks down walls), antimicrobial peptides (defensins, cathelicidins and histatins which disrupt the membranes of bacteria, fungi and virus)
How are pathogens recognised?
1.Self molecules (proteins, DNA, lipids,
Carbohydrates) are found on our
cells/tissues/organs (PAMPs).
2.Our immune system as it matures learns to recognise our own ‘self’ molecules and not react – tolerance.
3.In contrast we have evolved mechanisms to specifically recognise bacterial and viral Antigens
4.We have evolved families of cell-surface receptors that can distinguish self and non-self antigens (PRRs, TCRs, BCRs).
What are the cells of the immune system?
Cells of the innate immune system:
1. Granulocytes: Neutrophils, basophils, eosinophils, Mast cells
2. A-granulocytes: Monocytes (dendritic cells and macrophages)
3.Natural killer cells
Cells of the adaptive immune system:
1. T cell progenitor: helper, cytotoxic & memory T cells
2. B cell progenitor: Plasma and memory B cell
What is a neutrophil and what is its principal function?
1.Identified by a multi-lobed nucleus and granules.
2.Patrol the bloodstream and rapidly infiltrate tissue in the case of infection. Stains pink with H&E.
2Phagocytosis, Degranulation, Neutrophil extracellular trap (NET). Neutrophils die after this process.
What is a basophil/ mast cell and what is its principal function?
1.Basophils are circulating, mast
cells are resident in many tissues.
- Granules have histamine
- Stains dark purple with H&E.
- Plays a huge role in inflammation and allergy/asthma
What is a eosinophil and what is its principal function?
- Circulate
- Contain acidophilic granules containing toxic substances to kill target and proteins to trigger an inflammatory response (degranulation).
- Brick red stained with eosin, has 2 lobes
- Evolved to protect against parasites
What is a monocyte and what is its principal function?
- Circulate in the blood, 50% stored in spleen
- Differentiate into macrophages or dendritic cells
- Replenish tissue-resident cells or migrate to tissues in response to infection
What is a macrophage and what is its principal function?
- Infiltrating or tissue resident
(Liver= kupffer, lung= alveolar macrophages, CNS= microglia, bones= osteoclast) - Main function is phagocytosis to induce killing
What is a dendritic cell and what is its principal function?
- They are tissue resident and circulating
- Perform phagocytosis and present the antigens to T cells (antigen presentation)
What is a natural killer cell and what is its principal function?
- Lymphoid in origin but act rapidly thus are an innate immune cell
- Surveil and quickly kill virally-infected cells and
tumour cells - Contain cytotoxic granules: Perforin and Proteases
4.Create pores in target cells and cause cell death
What is a B cell and what is its principal function?
- Cell of adaptive immunity. Made and develops in BM. Activated by antigen to become a plasma cell
- Plasma cell is specialised to secrete antibodies that will recognise the antigen
- Antibodies are secreted forms of the BCR (single specificity). These circulate blood stream (globulins) and mucosal surface
What is a T cell and what is its principal function?
- Cell of adaptive immunity. Made in BM and develops in thymus. Differentiation continues after leaving thymus.
- Express TCR of a single specificity
- Two types:
-T helper cells (CD4+): 4 subsets that help to mount the appropriate immune response (Th1, Th2, Th17 & T regulator subsets)
-Cytotoxic T cells: kill infected or altered cell (killer T cell)
What are the primary lymph organs and what are their function?
- Bone Marrow:
- Hematopoietic organ. Source of all blood cells.
- Site of maturation of B cells, which contributes to humoral immunity. - Thymus:
- Site of development of T lymphocytes, which orchestrate adaptive immune responses.
What are the secondary lymph organs and what are their function?
- Lymph nodes:
- Encapsulated nodular aggregates of lymph tissue
located along lymph channels. Major centre of immune cells
- Lymph is drained here
- Site of B cell proliferation & generation of antibodies for specific antigen - Spleen:
- Major lymph and blood filtration organ
- Located in left cranial abdomen
-Stores and removes erythrocytes from blood and
filters blood for blood-borne infection - Mucosal and cutaneous lymphoid tissue:
- Nodes located under epithelial cells of skin, GI & respiratory tract
- Discrete collections of dendritic cells, macrophages, T and B cells
- Respond to microbes that breech the epithelial barrier
