What cells present antigen via MHC II? (What cells are Antigen Presenting Cells/APCs)?
- Answer Macrophages and dendritic cells (both derive from monocytes)
B-cells
All of these cells load their antigens onto MHC II proteins in the phagosome
Types of T cells - Answer CD8/Killer T cells: in response to antigen binding, secretes
chemical to kill cells infected by intracellular pathogen
CD4/Helper T cell: stimulate B-cell antibody production via cell-cell interaction. Further
defined by the types of cytokines they release.
TH0 cells are the initial response, releases cytokines and can be transferred to TH1 or
TH2
TH1 cells produce IFNgamma to activate macrophages and dendritic cells, promotes
intracellular (viral/bacterial) response and fungal response
Classes/isotypes of antibodies - Answer IgG (FIXES COMPLEMENT, most common
antibody)
IgA (ON MUCOUS MEMBRANES, doesn't fix complement)
IgM (FIXES COMPLEMENT)
IgD (receptor on B-cells)
IgE
Complement System - Answer Classical Complement Activation: Uses all components
C1-C9. ANTIBODY DEPENDENT, starts with C1 binding antibody that is bound to
bacterial surface.
Alternative Complement Activation: Free circulating C3b binds surface of bacterial cell.
Required FACTOR B, FACTOR D, C3 (a+b), C5 (a+b)
Mannose-Binding Lectin Activation: macrophage phagocytosis releases cytokines that
tells the liver to make lectin (which binds bacterial surface mannose). Uses C2, C4, C3
(convertase, a, and b), and C5
,Strep pyogenes treatment - Answer penicillin, amoxicillin, or cephalosporin
Strep pyogenes Virulence Factors - Answer Group specific carbohydrate (Lancefield
Antigen)
Fimbriae/pili
F protein (binds fibronectin to adhere to respiratory cells)
M protein (adhesion, inhibits C3b binding which inhibits opsonization)
Capsule
C5a peptidase (ScpA)
Strep toxins - Answer Streptolysin S (SLS) cytotoxin that disrupts membranes,
nonimmunogenic
Streptolysin O (SLO) cytotoxin that forms pore to lyse cell, very immunogenic (causes
beta hemolysis)
Streptococcal pyrogenic exotoxins (SpeA-D) acts as superantigen, need one of these to
be able to cause Scarlet Fever, Streptococcal Toxic Shock Like Syndrome, and
Necrotizing Fasciitis
Staph aureus treatments - Answer Flucloxacillin
For MRSA: vancomycin
Strep pyogenes diseases - Answer Pharyngitis
Scarlet Fever (untreated infection by strain that has Spe toxin): characterized by
strawberry tongue, rashes on chest and extremities
Rheumatic fever
Necrotizing fasciitis
Strep pyogenes diagnosis - Answer Rapid antigen test (tests for Lancefield A antigen by
swabbing oropharynx)
Beta hemolysis on BAP along with Gram + cocci chains
Exfoliative toxins (ETA and ETB or just ET toxins) cause SSSS by breaking down cell
junctions in the epidermis
Staph aureus surface proteins/virulence factors - Answer MSCRAMM binds elastin,
collagen, fibronectin to adhere to host cells
Protein A: binds the heavy chain Fc region (the bottom end) of antibodies (especially
IgG, but some IgM, E, and A) which blocks opsonization and inhibits complement
activation
Coagulase binds fibrin and converts to fibrinogen which causes clots which shields
bacteria from immune cells but makes it hard to disseminate.
Staph aureus diseases - Answer Mostly cutaneous infections, impetigo, with furuncles
and carbuncles
Toxic Shock Syndrome caused by TSST-1
Staphylococcal scalded skin syndrome (SSSS) caused by exfoliative toxin (ET toxins,
ETA and ETB) which breaks down cell junctions, causing the sloughing of epidermis.
S. aureus food poisoning (this is an intoxication, not infection)
Strep pneumoniae diseases - Answer Pneumonia
Sinusitis and otitis media (usually preceded by viral infection of URT) (otitis externa is
the one with seasonal incidence, not otitis media, but both are treated with antibiotic ear
drops)
Urine antigen test for C-polysaccharide/teichoic acid (doesn't have a Lancefield
antigen)
Strep pneumoniae virulence factors/toxins/important surface proteins for pathogenesis
- Answer Phosphorylcholine: binds platelet active factor (PAF) receptors which allows
bacteria to be transcytosed to the basolateral side of epithelial tissue
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