Humoral Immunity Terms Flashcards
Humoral Immunity Functions
-Host defense mediated by secreted Ig
Functions: - Neutralization
Opsonization-phagocytosis - Antibody Dependent Cellular Cytotoxicity
Complement Activation
Complement System Functions
- Lysis (MAC from C5b, C6,7,8,9)
- Inflammation (C3a and C5a)
- Phagocytosis (opsonized by C3b)
Fab
- Variable Ag binding site (N termini) made of L and H chains
- Cleaved from Fc by Papain
- Binds to Ag
Fc
- Made of constant H chains
- Cleaved from Fab by Papain
- Initiates complement activity
- Binds to cell receptors non immunologically to be able to move in body
- Has binding sites for other proteins and cells
- Deliver Ig to anatomical sites that would be otherwise inaccessible
- Link bound Ag to molecules/cells that affect their destruction
Thymus Independent Antigens (TI Antigens)
- Bacterial complex polysaccharides, lipopolysaccharides, peptidoglycans (are very distinct from mammalian products)
- Can activate naive B cells w/out CD4 T cell (Toll like receptor)
Thymus-dependent Antigens
- Activate B cells in secondary lymphoid tissue
- DC/APC+ specific Ag → Ag presenting to CD4 T cell → B cell activation
Clonal Selection
- B cell capable of responding to a particular Ag will be induced to produce Ig and differentiate into:
- Plasma cells, secrete Ig
- Memory B cells, capable of Ig response to any subsequent exposure of Ag
Isotype Switching
- Can occur as B cell response to infection progresses
- Diversifies functional properties of Fc region
- Can allow Ig to travel to different parts of body and attach Ag to molecules/cells for destruction
IgM
-1st Ig produced
-In blood and ECF
-Pentamer, valence is 10 (can efficiently bind microorganisms/Ag cant leave blood)
-Bind/activate complement
-No IgM Fc region receptors on phagocytic cells - cant recruit phagocytes
-Natural antibody
(Can bind specific Ag in absence of prior immunization)
-Helps prevent septicemia
IgG
- Second Ig response
- Dominant blood borne Ig
- Monomer
- Can go to extracellular spaces
- Bind/activate complement
- Can cross placental barrier (passive immunity for fetus)
- Helps prevent septicemia
IgA
-Monomeric: Provides Ig binding protection in fluids and tissues
-Dimeric: Protects surfaces of epithelial cells in contact w external enviro -Produced in MALT
(connective tissue that underlies basement membrane of mucosal epithelium)
-IgA secreting plasma cells on one side of epithelium and target Ags on other side
-Passed from mother → baby in breast feeding = passive immunity
IgE
- Binds to Fc receptor of mast cells/basophils/eosinophils
- Monomer
- Causes inflammation by binding mast cells in GI, resp. tract, dermis
- Once IgE binds to Fc receptor on mast cell, individual is sensitized to that Ag = allergic response
- Ag binding to FcERI receptors = immediate effector function
- Results are strong/quick
- Individual cells can have polyspecificity
IgD
- Function unclear
- May substitute IgM functions when IgM isn’t present
- Monomer
Neutralization
-Ig prevents bacterial/ toxin/virus adherence
-Bacteria binds to cell via adhesisn
→ B cell ingests virus + adhesins → produces adhesin antibody → Ig blocks adhesin binding
-B cell binds virus via coat protein → internalizes/degrades it
→ Presents viral peptides to T cell → activates B cell → B cell produces virus coat protein Ig →
Ig blocks binding to virus receptor
Opsonization
-Ig promotes phagocytosis
Fc: Ig coats bacteria → Ig binds Fc on phagocytic cell → bacteria engulfed → phagocytosis
C3b: Complement cascade activation → C3b cleavage from C3 → Complement fixation (C3b binds pathogen surface → aids in opsonization
