Immunology Notes

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Western University
Microbiology and Immunology
Microbiology and Immunology 3300B
Rodney Dekoter

Immunology NotesSept 1312 Innate immunity Functions without antigens and is immunity derived from nonantigen recognition of pathogens and passive mechanisms like barriers It is generated from germline encoded genes and is inheritable It recognizes general features of pathogens no fine specificity and has no memory of past pathogen encounters It is a mixture of physical barriers chemical defenses and cellular responses It is present in all individuals at all times Adaptive immunity Recognizes antigens produced by pathogens It is immunity directed against antigens It is generated by recombination of genes in somatic cells and is not inheritable It recognizes specific antigens fine specificity and has memory of past antigens It involves cellular responses and is generated as pathogens are encountered Evolution of the immune system foreign DNA and barriers selfnonself immune cells specialized immune cells and enzyme cascades antibodylike genes adaptive Epithelium is specialized tissue that provides the first line of defense against infection It is our barrier with the outside world Epithelial cells are held together by tight junctions located between the cells very restrictive The basement membrane located on the inner side of the cells gives the cells mechanical strength Cilia are located on the outer side of the cells and they sweep mucus that has been secreted by goblet cells out which traps and ejects pathogens Chemical defenses in epithelium Lysozyme is a glycosidase that degrades the bacterial cell wall Peptidoglycan is present on the outer side of the cell membrane of bacteria and is composed of alternating sugars Lysozyme cleaves the 14 bond between these two sugars GlcNAc and MurNAc creating a defect in the peptidoglycan layer and exposing the underlying cell membrane to other antimicrobials It exposes the lipid bilayer of the bacteria allowing it to be killed It is stronger against grampositive bacteria than gramnegative bacteria Gramnegative bacteria have an outer layer of lipopolysaccharide LPS covering the peptidoglycan making it less accessible Chemical defenses in epithelium Secretory phospholipasesPL is an enzyme that can enter through the open bacterial cell wall and hydrolyzes phospholipids in the cell membrane degrades pathogen plasma membrane It breaks down the lipid bilayer by cutting the hydrophobic tails off of the phospholipids killing the bacteria Chemical defenses in epithelium Defensins and cathelicidins are attracted to charged bacterial membranes and insert their hydrophobic region into the membrane bilayer which forms a hole or pore and makes the membrane leaky The amphipathic domain must be cleaved by proteases to be activated this happens once they are released from the cell or when they enter the phagosome Ctype lectins bind to peptidoglycans in bacterial cell walls and exert direct bactericidal activity They bind to unique carbohydrates found on the surface of bacteria and kill bacteria by disrupting the bacterial membrane The carbohydrate recognition domain of lectin must be cleaved to be active Defensins are amphipathic peptides that disrupt the cell membranes of microbes They have a positive end and a hydrophobic end The positive end is attracted to the charged surface of the cell membrane and it becomes inserted in the lipid bilayer The defensins rearrange themselves within the membrane creating holes or pores which results in lysis of the pathogen Detection of self Innate immune cells have receptors on their surface that bind to our own cells MHCbunding receptors sialic acid and glycosaminoglycans keep molecules from inserting into our cells are other mechanisms of innate selfrecognition Detection of nonself Pattern recognition receptors PPRs on the surface on innate immune cells such as macrophages neutrophils and dendritic cells recognize pathogenassociated molecular patterns PAMPs that are present on pathogens but not on the bodys own cells These are things
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