The Immune Response to Infection

Question 1

Which antibody is present in secreted mucous?

Answer 1

IgA

Question 2

What are the polymorphonuclear cells?

Answer 2

Neutrophils

Eosinophils

Basophils

Mast cells

Question 3

What are the mononuclear cells?

Answer 3

Monocytes

Macrophages

Question 4

What is the difference between monocytes and macrophages?

Answer 4

Monocytes are produced in the bone marrow, circulate in the blood and migrate to tissues where they differentiate into macrophages.

Question 5

What do macrophages differentiate to in the liver?

Answer 5

Kupffer cells

Question 6

What do macrophages differentiate to in the kidneys?

Answer 6

Mesangial cells

Question 7

What do macrophages differentiate to in the bone?

Answer 7

Osteoclasts

Question 8

What do macrophages differentiate to in the spleen?

Answer 8

Sinusoidal lining cell

Question 9

What do macrophages differentiate to in the lung?

Answer 9

Alveolar macrophages

Question 10

What do macrophages differentiate to in neural tissue?

Answer 10

Microglial cells

Question 11

What do macrophages differentiate to in connective tissue?

Answer 11

Histiocyte

Question 12

What do macrophages differentiate to in the skin?

Answer 12

Langerhans cell

Question 13

What do macrophages differentiate to in the joints?

Answer 13

Macrophage-like synoviocytes

Question 14

How do immune cells detect pathogens?

Answer 14

Express pattern recognition receptors

Express Fc receptors for Ig

Question 15

How are phagocytes recruited?

Answer 15

Cellular damage and bacterial products trigger the local production of inflammatory cytokines and chemokines which leads to either cytokines activating the vascular endothelium, thus enhancing permability OR chemokines attracting the neutrophiles

Question 16

How do immune cells recognise pathogens?

Answer 16

PRR e.g. toll-like receptors and mannose receptors which recognise generic motifs known as pathogen-associated molecular patterns (PAMPs), e.g. bacterial sugars, DNA, RNA.

Question 17

What happens during opsonisation?

Answer 17

Opsonisation facilitates endocytosis by covering the pathogens to attract neutrophils and macrophages

Question 18

What are opsonins?

Answer 18

Act as a bridge between the pathogen and the phagocyte receptors; they include:

Antibodies binding to Fc receptors

Complement components binding

Question 19

What are the two methods of killing pathogens?

Answer 19

Oxidative

Non-oxidative

Question 20

What is oxidative killing?

Answer 20

NAPDH oxidase complex converts oxygen into reactive oxygen species e.g. Hydrogen peroxide, superoxide.

Myeloperoxidases catalyses production of hydrochlorous acid from hydrogen peroxide and chloride.

Hydrochlorous acid is a highly effective oxidant and anti-microbial.

Question 21

What is non-oxidative killing?

Answer 21

Within the granules there are bacteriocidal enzymes that each have a unique
antimicrobial spectrum, resulting in broad coverage against bacteria and fungi

e.g. Lysozyme which can kill and lyse bacterial cell wall and lactoferrin to deprive iron. These are released.

Question 22

How do phagocytes die?

Answer 22

As the cells die, residual enzymes are released causing liquefaction of closely adjacent tissue.

Accumulation of dead/dying neutrophils within infected tissue results in the formation of pus.

Extensive localised formation of pus causes abscess formation.

Question 23

How do NK cells function?

Answer 23

Express inhibitory receptors for self-HLA which are usually dominant, as well as other receptors as well. If the target cell does not express self-HLA then apoptosis will be induced.

Question 24

Which HLA type do dendritic cells express?

Answer 24

HLA class I

Question 25

What are the primary lymphoid organs?

Answer 25

Organs involved in lymphocyte development.

Bone marrow - T and B cells are derived from haematopoietic stem cells and B cells mature.

Thymus - T cell maturation. Thymus is most active in foetal and neonatal period, involutes after puberty.

Question 26

What are the secondary lymphoid organs?

Answer 26

Anatomical sites of interaction between naïve lymphocytes and microorganisms.

Spleen

Lymph nodes

Mucosal associated lymphoid tissue

Question 27

What are CD4+ T cells?

Answer 27

Recognise peptides derived from extracellular proteins presented on HLA Class II molecules (HLA-DR, HLA-DP, HLA-DQ).

Perform immunoregulatory functions via cell-cell interactions and
expression of cytokines. Specifically provide help for development of full B cell response and help for development of some CD8+ T cell responses.

Many different CD4 subtypes, different cytokines encourage
development along different routes. T reg keep the immune system under control, inhibitory. Follicular helper T cells involved in development of B cell responses.

Question 28

What are CD8+ T cells?

Answer 28

Specialised cytotoxic cells,. Recognise peptides usually derived from intracellular proteins in association with HLA class I (HLA-A,B, C).

Kill cells directly with perforin (forms pore and then empties
granzymes into the pore) and express Fas Ligand (Death receptor). Secrete cytokines e.g. IFNy and TNFa.

Particularly important in defence against viral infections and tumours.

Question 29

What is the function of B-lymphocytes?

Answer 29

Secrete antibodies

If they do not come into contact with an antigen, they secrete IgM, if so, they can secrete IgA, IgG and IgE after priming of CD4 cells by the dendritic cells (CD40-CD40L interaction required).

Question 30

What are the three pathways of complement cascade?

Answer 30

Classical

Mannose binding lectin pathway

Alternative

Question 31

What is the classical pathway?

Answer 31

C1, C2. C4

Activated by antibody-antigen immune complexes, results in change in antibody shape that exposes binding site for C1.

Binding of C1 to the binding site on antibody results in activation of the cascade.

Dependent upon activation of acquitted immune response (antibody) so doesn’t occur very early in infection.

IgG binds pathogens and these complexes than activate the complement pathway.

Question 32

What is the mannose binding lectin pathway?

Answer 32

C4. C2

Activated by the direct binding of MBL to microbial cell surface carbohydrates.

Directly stimulates the classical pathway via C4 and C2 but not C1. Not dependent on acquired immune response.

Question 33

What is the alternative pathway?

Answer 33

Directly triggered by binding of C3 to the bacterial cell wall components e.g. lipopolysaccharide of gram negative bacteria or teichoic acid of gram positive bacteria.

Not dependent on acquired immune response.
Involves factors B, I, and P.

Question 34

How is the final common pathway (C5, C9) triggered?

Answer 34

The three pathways converge on C3 which activates final common pathway (C5, 9) and forms the activate the membrane attack complex.

C3 activation is major amplification step, triggers the formation of the membrane attack complex via C5 to C9. MAC makes holes in membranes.

Question 35

What are cytokines?

Answer 35

Small protein messengers that have immunomodulatory function. Can act back on same cell (autocrine) or on other cells (paracrine) dependent action. Examples include IL-2,6,10,12, TNFa, TGFb.

Question 36

What are chemokines?

Answer 36

Subset of cytokines, Chemotactic cytokines ie chemoattractant involved in direct recruitment/homing of leukocytes in an inflammatory response.

CCL19 and CCL21 are ligands for CCR7 and important in directing dendritic
cell trafficking to lymph nodes. Other examples of chemokines include IL8, RANTES, MIP-1 alpha and beta.

Chemokine receptors can act as co-receptors for HIV.