Stanford Microbiology and Immunology 104 204 Innate Immunology Lecture 5 Barrier epithelia and antimicrobial peptides Structure of a lung Trachea lead to bronchi to bronchioles to alveoli It is a dead end structure that must deal with inhaled particles which would otherwise accumulate in the alveolae Mucus escalator In the bronchioles the mucus escalator moves material up to the throat This escalator functions in the eustachian tubes nose and lungs Think of the escalator as moving flypaper that traps particles and moves them out of the lung The bronchiolar epithelia are composed of epithelia cells with many cilia goblet cells that secrete mucus and mucus glands In an uninfected state the mucus glands produce most of the mucus but during an infection the goblet cells are induced to produce large amounts of mucus resulting in the production of phlegm Alveoli This is the location where oxygen and carbon dioxide are exchanged A thin epithelium is in close contact with capillaries allowing rapid gas exchange Alveolar lumen contains Macrophages Complement Antibodies IgA Surfactant also an opsonizing lectin Alveolus is a dead end it contains no cilia and cannot cough things out Particles must be removed by macrophages Infection and biowarfare considerations Particles above a certain size 10 um will contact the mucus lined walls of the bronchioles and be swept from the lungs Inhaled pathogens that survive in the alveolae must be smaller than this in the 1 5 m range we remember from the anthrax mail case How do you defeat the innate immune system in the lungs Streptococcus pneumoniae Colonizes nasopharynx Cilliary paralysis following influenza dependent upon the influenza virus allows the bacteria to enter the lung Capsule prevents phagocytosis by macrophages Virulence factor pneumolysin may inhibit ciliated cells Other bugs that do similar things Mycoplasma pneumonaie enter epithelia Stanford Microbiology and Immunology 104 204 Innate Immunology Bordetella pertussis bind microvilli Pseudomonas aeruginosa inhibit cilia beating Chlamydia pneumoniae inhibit cilia beating Neisseria meningitides bind microvilli Anthrax Not a common inhaled pathogen but worth discussing because of the public discussion of particle size Spore clusters must be in smaller than 5 microns to make it into the alveoli without being caught in the escalator The spores are taken up by macrophages in alveoli and germinate within these cells The germinated cell does not appear to divide during its life within the macrophage The germinated cell lyses the lysosomal membrane and lives within the cytoplasm The macrophage moves a lung lymph node where the infection proceeds Upon release from the macrophage vegetative anthrax cells develop a capsule and are no longer phagocytosed Tuberculosis Mycobacterium tuberculosis is infectious through the air This microorganism has evolved methods of surviving for long periods in infected macrophages we ve seen this approach before with microorganisms like Salmonella which can survive an inflammatory event by living within a macrophage Infections of insect tracheoles Will show below that they react by producing antimicrobial peptides It is difficult for them to remove particles there are no macrophages Perhaps as a result of this parasitic mites can live within the trachea of honey bees Insects do not use a mucus layer in the same manner as vertebrates do It is important from a public health point of view as microbes vectored by insects must cross this barrier Insect guts are protected by a peritrophic matrix a highly crosslinked chitin and protein containing semi permeable membrane There are at least three types of peritrophic matrix 1 no matrix 2 Type I matrix synthesized post meal 3 Type II matrix continuously synthesized Stanford Microbiology and Immunology 104 204 Innate Immunology Malaria parasite uses chitinase to cut through this layer after it has formed Baculoviruses carry a virulence protein that degrades mucus Secreted antimicrobial peptides Humans continuously secrete antimicrobial peptides and proteins and can deliver them upon activation by epithelia and immune cells Nasal fluid is a good example of a fluid containing antimicrobial peptides Some antimicrobials are Lysozyme cleaves peptidoglycan recent discussions suggest that it might play an important role in clearing bacterial products to limit inflammation Lactoferrin sequesters iron blocks biofilm development of pseudomonas auriginosa Alpha and Defensins antimicrobial peptides Can be antibacterial fungal viral or in plants anti insect The list of antimicrobial peptides is growing and it is difficult to state exactly how many families of peptides exist In humans there are defensins defensins Cathelicidin HNP1 4 granulocytes HNP5 paneth cells of gut genital tract hBD 1 2 skin lung gut epithelia hBD 3 skin lung tonsils hBD 4 testis Gastric antrum LL 37 granulocytes lung skin testis gut l lymphocytes In humans alpha and beta defensins differ by where they are expressed granules vs epithelia but this is not the case in other creatures They can be distinguished by the order of their 3 disulfide bonds In flies there are arguably 4 groups of peptides in addition lysozymes helical linear cecropin open ended cyclic defensin drosomycin anti fungal Proline rich drosocin Metchikowin Glycine rich diptericin attacin Stanford Microbiology and Immunology 104 204 Innate Immunology In addition there are newly discovered families of cyclical peptides theta defensins and others These small peptides were identified first in the cecropia moth and rabbit neutrophils and were not regarded as being of general interest until their discovery in frogs of all things Cecropia were a useful tool as the pupae overwinter and shut down most of their metabolism in a refrigerator but still raise a rapid immune response and they are relatively large insects The immune response is easy to spot as new protein synthesis Synthesis of peptides All are secreted proteins made with at least a signal sequence defensins are synthesized as pre pro proteins and the pro form is stored in granules In humans these are secreted into the lysosome of neutrophils defensins contain only a pro sequence and are secreted directly into the extracellular milieu Cathelicidins are broadly found throughout mammals These are unusual in that their pro region cathelin is highly conserved and was identified first The actual antimicrobial peptides are highly variable and are cleaved from