Download The Immune System of the Upper Respiratory Tract

Location
Host Defense Mechanism*
Upper Airways (trap particles > 10 um)
Nasopharynx
Nasal hair
Turbinates
Waldeyer’s Ring: pharyngeal and tubal tonsils
(pathologies: acquired or congenital
immundeficiency disorders, lymphomas, CLL,
myeloma)
Mucociliary apparatus (pathologies: increased
mucosal viscosity & thickness: CF, asthma, chronic
bronchitis OR
Mucocilliary dyskinesia due to smoking,
anaesthetics, bronchiectasis, immotile cilia
syndrome)
IgA secretion (selective IgA deficiency: common
1:400)
Location
Host Defense Mechanism*
Upper Airways (trap particles > 10 um)
Oropharynx
Saliva (contains fibronectin, IGA, lactoferrin,
lysozyme, peroxidase, secretory leukocyte
proteinase inhibitor. (Saliva secretion reduces with
ageing)
Waldeyer’s Ring palatine and lingual tonsils
(pathologies: acquired or congenital
immundeficiency disorders, lymphomas, CLL,
myeloma)
Sloughing of epithelial cells
Cough reflex (pathologies: CVA, ventilator, lung
transplant, elderly, neonates, smoking, paralysis,
neuromuscular disorders)
Complement production (low levels C3 & C4 with
SLE)
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The MALT tissues relevant to the respiratory
system are:
NALT (Waldeyer’s ring of tonsilar tissue from
the upper nasopharynx (adenoids) to the
posterior tongue – inducer and effector
LALT laryngeal lymphoid tissue
BALT (bronchus associated lymphoid tissue:
found in peribronchial, perivascular and
interstitial areas of the lung
Conducting Airways (trap 2-10 um particles)
Sharp-angled branching of airways (particle
Trachea & Bronchi
forward momentum causes lodgement in
airway surface liquid)
Mucociliary apparatus
Airway surface liquid (lysozyme, lactoferrin,
secretory leukocyte proteinase inhibitor)
Dendritic cells
Antigen processing
and presentation to
Bronchus-associated Th lymphocyte →
stimulation of
lymphoid tissue
memory and effector
(BALT)
T cells and B cells
Immunoglobulin production (IgG, IgM, IgA)
Lower Respiratory Tract (most bacteria are 0.5-2 um and can reach alveoli)
No mucocillary apparatus but alveolar lining fluid
Terminal airways, alveoli contains surfactant, FFAs, fibronectin, IGG,
complement, iron-binding proteins)
Alveolar & intravascular macrophages
(phagocytosis, cytokines)
Neutrophil recruitment
(pattern recognition receptors→transcription factor
stimulation→proinflammatory and antiinflammatory cytokine and chemokine production)
Interstitial macrophages
(lung connective tissue)
Dendritic cells (alveolar
septa)
Bronchus-associated
lymphoid tissue (BALT)
Antigen processing and
presentation to CD4+Th
& secretion of
cytokines→
stimulation of effector T
cells (by IL2) and B cells
(by IL4, IL13 & IFN-γ)
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Impaired epiglottic closure: stroke, seizure, drug
abuse, normal sleep -> aspiration of oropharyngeal
flora
Alcohol
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Impairs epiglottic and cough reflex
Alters colonisation of oropharynx – G+ve to G-ve
Decreased neutrophil mobilisation & effectiveness
Blocks TNF response to endotoxin
Induces macrophage secretion of IL10 (antiinflammatory)
Tobacco impairs mucociliary & macrophage
functions
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Mycoplasma and H.influenza
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Influenza A
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Impair ciliary function
Destroys cilia causing mucus buildup and 2nd infections
Extrapulmonary sepsis decreases lung clearance of bacteria
Burn inhalation injury with ventilator support (50% incidence of
pneumonia, 37% mortality rate).
Drugs: especially cancer chemotherapy, immunosuppressants, proton
pump and H2 inhibitors
Other factors that impair pulmonary host defenses include old age,
premature birth, hypoxaemia, acidosis, toxic inhalations, pulmonary
oedema, malnutrition
Lymphadenopathy due to compression from sarcoidosis, solid tumours
Bronchial obstruction due to adenocarcinoma
Systemic disease: diabetes, renal failure, GORD, COAD, CHF, HIV
Splenectomy: encapsulated bacteria like S.pneumoniae must be
opsonised then removed by splenic macrophages, or else!