IMMUN: Respiratory Immunology

Question 1

what does BALT stand for and where is it located within the tissue?

Answer 1

• bronchus-associated lymphoid tissue
• located in lamina propria

Question 2

what does the lamina propria contain? (immune wise)

Answer 2

• BALT
• plasma cells
• Tc cells
• macrophages
• mast cells

Question 3

mucociliary escalator

Answer 3

• goblet cells in epithelium secrete mucus
• cilia (pseudostratified ciliated columnar epithelium) beat in an asymmetric rhythm
• mucus moves 1cm/minute

Question 4

what can interfere with the mucociliary escalator

Answer 4

• smoking
• anaesthetic
• infection
• immotile cilia syndrome
• CF (makes mucus thicker)

Question 5

function of respiratory epithelial cells

Answer 5

• express PRRs which recognise PAMPs
• secrete chemokines and cytokines to recruit immune cells
• secrete antimicrobial compounds e.g. defensins into the lumen of the airway

Question 6

two types of lung macrophages

Answer 6

• alveolar: phagocytose inhaled particles
• interstitial: activated if epithelial barrier is breached

Question 7

why are neutrophils a good inflammatory marker?

Answer 7

• in healthy lungs: they are found in blood, not in lung tissue
• in an infected lung, they are recruited so good marker of inflammation

Question 8

how can immune cells capture antigens?

Answer 8

• dendritic cells can extend their ‘arms’ across the epithelium and capture antigen from airway lumen
• M(icrofold) cells lining the epithelium take antigen from lumen to basal surface, where it is taken up by APCs

Question 9

3 APCs

Answer 9

• dendritic cell (best)
• macrophage
• B lymphocyte

Question 10

2 types of IgA

Answer 10

• serum IgA (IgA1 monomers) = pro-inflammatory (leads to phagocytosis, cytokines etc)
• secretory IgA (IgA2 dimers) = non-inflammatory = neutralisation of pathogens, toxins and antigens in lamina propria or airway lumen

Question 11

how does secretory IgA move from the lamina propria to airway lumen

Answer 11

• made in lamina propria by plasma cells
• transported to mucosa via poly-Ig receptor
• poly-Ig receptor cleaves - the ‘secretory component’ remains attached to IgA and prevents secretory IgA from binding to Fca receptor on innate immune cells = non-inflammatory

Question 12

why is secretory IgA non-inflammatory?

Answer 12

• b/c we want to be gentle to our own microflora since much of it is in the mucosa

Question 13

how is all the mucosa in the body connected (immune-wise)?

Answer 13

• mucosal lymphocytes express their own homing receptors which are diff to other lymphocytes
• therefore they will circulate in mucosa all around the body

Question 14

how do innate immune cells recognise pathogens?

Answer 14

• detect PAMPs and DAMPs (damage-associated) using pattern recognition receptors (PRRs)
• e.g. lipopolysaccharides in gram-negative bacteria

Question 15

lineage of T cells

Answer 15

Question 16

sensitisation (first step in allergy)

Answer 16

• allergen enters body and is phagocytosed (if skin > langerhans cell or if elsewhere, dendritic cells)
• presented to naïve Th cell on MHC II marker> TH2 cell secretes IL-4,5,13
• B cells differentiate into plasma cells > secrete IgE (class switching due to IL-4) which binds to mast cell and basophils by Fc region

Question 17

allergic response (second step)

Answer 17

• upon secondary exposure to allergen, allergen binds to IgE on mast cells > crosslinks
• leads to degranulation and release of histamine > allergic response
• 2 phases: immediate reaction phase using existing chemical mediators (histamine) or late reaction phase using new chemical mediators (phospholipids, arachidonic acid, cytokines, prostaglandins)

Question 18

pathological features of the asthmatic lung

Answer 18

• goblet cell hyperplasia > excessive mucus > wheezing
• remodelling of lung tissue = collagen deposition = less elasticity
• eosinophils = Th2 response

Question 19

why is IgE involved in allergies?

Answer 19

• IgE evolved to protect from helminths and is essentially doing the same thing to allergens

Question 20

allergen immunotherapy

Answer 20

• subcutaneous injection of allergen to induce immunological and physiological tolerance
• diverts Th2 response towards Treg and Th1

Question 21

4 main lung lymph nodes

Answer 21

• pulmonary: angles of bifurcation of branching lobar bronchi
• bronchopulmonary (hilar)
• tracheobronchial: above/below bifurcation of trachea
• paratracheal: next to trachea