Host defences

Question 1

What is the role of the immune system?

Answer 1

To protect against invasion of pathogenic microorganisms, by recognizing and responding to them. Able to generate cells and molecules that can recognise and eliminate foreign invaders

Question 2

What is the difference between the innate and the adaptive immune system?

Answer 2

the innate system had most components present before onset of infection, it’s the first line of defence, rapidly evoked and uses non-specific mechanisms however the adaptive immune system needs an antigen present, is activated slowly, is specific and has memory

Question 3

What are some innate mechanisms?

Answer 3

physical barriers such as skin and mucous, physiologic barriers such as temperature and pH, phagocytosis and inflammatory defensive barriers such as vasodilation and increase in capillary permeability

Question 4

What are the 3 major interfaces between the body and the external environment?

Answer 4

skin, GIT, respiratory tract

Question 5

What are the soluble factors in the innate immune system and their function?

Answer 5

lysozyme which splits the bacterial cell wall, acute phase proteins, complement and interferon prevents virus from replicating

Question 6

What are the cells in the innate immune system and their function?

Answer 6

phagocytes such as macrophages which engulf particles/ used for tissue repair/used for antigen representation in specific immune response, NK cells which recognise cell surface changes occurring on virally infected and tumour cells, Neutrophils take up and kill extra cellular microorganisms. Eosinophils which gather at parasite infection or allergic reaction and release toxins in granules also damage parasite membrane. Basophils are full of granules containing histamine,involved in allergic reactions

Question 7

What do all cells in the immune system arise from?

Answer 7

pluripotent stem cells: myeloid (innate) and lymphoid lineage (adaptive)

Question 8

What growth factor does the development of cells from stem cells involve?

Answer 8

cytokine growth factor

Question 9

What are the stages of phagocytosis?

Answer 9

ingestion of microbes to form a phagosome, metabolic reactions occur in phagosome membrane which generate toxic products such as oxygen and nitrogen radicals which help ingest microbe, phagolysosomes formed by fusion of phagosome with lysosomes which contain damaging enzymes and cationic proteins

Question 10

What are natural killer cells and explain the action of these cells

Answer 10

a distinct type of cytotoxic lymphocyte produced in bone marrow, main function is to attack and kill infected cell using 2 mechanisms. They have Fc receptors to recognise specific antibodies bound to infected cells and kill them. Also able to recognise and kill infected cells by their reduced expression of MH class 1 molecules. They have 2 types of surface receptors which control cytotoxic activity: one is an activating receptor which triggers killing by NK and another inhibits activation to prevent them from killing normal host cells

Question 11

Describe the innate immune response

Answer 11

tissue damage causes release of vasoactive and chemotactic factors which trigger local increase in blood flow and capillary permeability, permeable capillaries allow influx of fluid and cells, phagocytes migrate to site of inflammation, they then destroy the bacteria

Question 12

What cells are involved in the adaptive immune system?

Answer 12

B lymphocytes which produce plasma cells, T lymphocytes which produce T helper CD4+ & T cytotoxic CD8+ cells

Question 13

What do T Helper CD4+ cells do?

Answer 13

They recognise antigen presented on MHC class II molecules by APCs. Categorized into T Helper 1 and T helper 2. T helper 1 produces specific cytokines such as interferon gamma which activates macrophages and stimulates cell mediated immunity and T Helper 2 produces different types of cytokines such as the interleukiene 4 and 6 which stimulate growth of plasma cell clones and antibody secretion. They also stimulate specific immunity

Question 14

What do T cytotoxic CD8+ cells do?

Answer 14

eliminates cells infected with virus or bacteria living in cytosol. When foreign protein binds then specific CD8+ T cells are activated and become effector CD8+ T cells that can directly and rapidly kill any cell with the same antigen

Question 15

What is the purpose of B cells?

Answer 15

activated to produce antibodies. They bind to antigens and bring them inside via endocytosis then the internalised antigen is broken in fragments ant taken back to surface by MHC class II proteins

Question 16

How do t cells and B cells interact?

Answer 16

T helper cells help B cells divide and produce antibodies. B cells present antigen to T helper in order to trigger cytokine release which signals the B cell to divide and secrete the antibodies. T helper cells only help B cells that recognise the same antigens as them making the response very specific

Question 17

What are the characteristics of the adaptive immune system?

Answer 17

activated later during infection, specific, diverse and has memory. Develops later and requires activation of lymphocytes. Different receptors involved depending on the antigen that causes infection.

Question 18

What is the complement system and describe its activation?

Answer 18

Complement system consists of small proteins in blood, when stimulated proteases in the system cleaves specific proteins to release cytokines and initiate a cascade of further cleavages. The end result is the massive amplification of the response and activation of cell killing membrane complex

Question 19

What are dendritic cells?

Answer 19

Highly specialised WBCs found in skin. Mucosa and lymphoid tissues.
They initiate primary response by activating lymphocytes and secreting cytokines. They are efficient APCSs

Question 20

What are antibodies and what is their function?

Answer 20

Protein tetramers which consist of 2 light and 2 heavier chains. Their role is to bind tightly to antigens. A few things can occur when an antibody encounters a foreign antigen: opsonisation which involves binding of opsonin to membrane which attracts phagocytes to the pathogen, neutralization, complement activation or antibody dependent cytotoxicity ADCC

Question 21

What is the Humoral response?

Answer 21

defence mechanism against extracellular microbes and their toxins. Also called antibody mediated response, B lymphocytes secrete antibodies that attack by one of the 4 ways mentioned.

Question 22

What is the cell mediated response?

Answer 22

defence mechanism against intracellular microbes, involves both types of T cells. T helper cell which secretes cytokines and stimulates proliferation and differentiation of T cells and other cells. Cytotoxic T cells act by lysing the infected cells. The lysis is achieved by releasing perforin which makes holes in target cell allowing entry of granzyme B then apoptosis

Question 23

What are the characteristics of a vaccine?

Answer 23

vaccine immunogenicity is the ability of it to produce antibodies/ vaccine efficacy is the reduction in the incidence of a disease among people who’ve received a vaccine / vaccine effectiveness id the ability of vaccine to protect community