Topic 1: Introduction:

Question 1

What are the 3 layers of defence of the immune system?

Answer 1

1. Physical barriers: physical structures e.g. skin, mucous lining; to keep the pathogen out
2. Innate Immune Response: rapid response once the pathogen enters the body aimed at dealing with the threat occurs in minutes to hours
3. Adaptive Immune Response: very specific response to a target which takes longer to develop but provides the immune system with memory of the pathogen and ongoing protection

Question 2

Describe innate immunity and some of the components that make it up:

Answer 2

• Immune response that provides protection against infection by mechanisms that existed before infection
• Rapid
• Responds the same to the pathogen every time; even after repeated infections
• Made up of:
  1. Epithelial barriers (skin, muscosal membranes)
  2. Phagocytic cells (neutrophils and macrophages)
  3. NK cells (cytotoxic cells that recognise infected/tumourous cells without antibodies)
  4. Complement system (small proteins in blood that enhance the function of antibodies and phagocytic cells
  5. Cytokines- mainly produced by mononuclear phagocytes that regulate and control many functions of the immune cells

Question 3

What is adaptive immunity?

Answer 3

• A more complex antigen specific immune response
• It is a slower response as antigens must first be processed by antigen presenting cells and then B and T cells with complementary receptors for that antigen must undergo clonal expansion
• Divided into a humoral response (B cells bind ‘whole’ antigen in fluid and release antibodies) and the cellular response (T-cells recognise antigen proteins presented by MHC II on APCs and proliferate into helper T-Cells and cytotoxic T-cells which target infected cells in the body)
• This response results in the production of B and T memory cells specific to the antigen and therefore provides the body with immunological memory

Question 4

What are primary lymphoid organs?

Answer 4

• Sites where the cells of the immune system are generated and/or matured
  1. Bone marrow
  2. Thymus

Question 5

What are secondary lymphoid organs?

Answer 5

• Collective structures where an adaptive immune response is generated
  1. Lymph nodes: tonsils, Peyer’s patches, linguinal nodes etc.
  2. Spleen: deals with circulating blood

Question 6

Describe the function and structure of a lymph node:

Answer 6

• Small nodular encapsulated aggregates of lymphocyte-rich tissue situated throughout the body where adaptive immune responses to antigens are initiated
• Structure: nodule coated by the capsule and subcapsular sinus, interspersed with trabeculae.
• The outer portion contains B cell zones (with germinal centres) and more proximally T cell zones which contain high endothelial venules
• The inner portion of the node is the medulla
• The bottom of the node central to the medulla is the hilium where efferent lymphatic vessels exit and the blood supply enters/exits

Question 7

Describe the function and structure of the spleen:

Answer 7

• Secondary lymphoid organ in upper left quadrant of the abdomen
• Major site of adaptive immune responses to blood-borne pathogens
• Contains:
• Red pulp: blood filled vascular sinusoids lined by phagocytes to ingest opsonised antigens and damaged RBCs
• White pulp: contains lymphocytes and lymphoid follicles where B cells are activated

Question 8

Describe the function and structure of the thymus:

Answer 8

• Primary lymphoid organ where the maturation of T lymphocytes occurs
• Consists of an outer cortex: packed with immature and maturing T cells (thymocytes) that will undergo further maturation as they move into the central part of the thymus (the medulla)
• The medulla contains T-lymphocytes and epithelial cells (that support the thymus and help develop tolerance against self antigens). Also contains Hassall’s corpuscles
• The thymus degnerates with age

Question 9

Describe haematopoietc stem cells:

Answer 9

• Found in the bone marrow
• An undifferentiated bone marrow cell that divides continuously and gives rise to additional stem cells and cells of multiple different lineages. These cells in the bone marrow will give rise to cells of the
  lymphoid, myeloid, and erythrocytic lineage

Question 10

Describe the lymphatic system:

Answer 10

A system of vessels throughout the body that collects tissue fluid called lymph, originally derived from the blood, and returns it, through the thoracic duct, to the circulation. Lymph nodes are interspersed
along these vessels and trap and retain antigens present in the lymph.

Question 11

Describe a neutrophil:

Answer 11

• They are the most abundant type of circulating white blood cells and are the major cell type mediating acute inflammatory responses to bacterial infections.
• A phagocytic cell characterized by a segmented lobular nucleus and cytoplasmic granules filled with degradative enzymes.

Question 12

What are myeloid cells?

Answer 12

Refers to the lineage of blood cells that includes all leukocytes except lymphocytes.

Question 13

What is a macrophage?

Answer 13

• A tissue-based phagocytic cell derived from blood monocytes that plays important roles in innate and adaptive immune responses.
• These cells are activated by microbial products such as endotoxin and by T cell cytokines such as IFN-γ. Once activated, these cells phagocytose and kill microorganisms, secrete proinflammatory cytokines, and present antigens to helper T cells.

Question 14

Describe a basophil:

Answer 14

• Type of granulocyte (PMN)
• Structural and functional similarities to mast cells
• Express a high affinity for IgE
• Recruited into tissues where antigen is present and may contribute to immediate hypersensitivity reactions
• Large cytoplasmic granules often obscure nucleus when stained

Question 15

Describe a dendritic cell:

Answer 15

• Characterised by thin membranous projections (dendrites)
• Presents antigens on MHC II markers (mainly to naive T cells)
• Key role in bridging the gap between innate and adaptive immunity

Question 16

Describe a eosinophil:

Answer 16

• A type of granulocyte
• Characterised by a 2 lobed nucleus and a red/pink appearance when stained with eosin
• Abundant in the inflammatory infiltrates of immediate hypersensitivity late-phase reactions and that contributes to many of the pathologic processes in
  allergic diseases
• Important in defense against
  extracellular parasites, including helminths

Question 17

What are granulocytes/polymorphonuclear leukocytes?

Answer 17

• White blood cells with multilobed nuclei and cytoplasmic granules.
• They comprise the neutrophils, eosinophils, and basophils