Immuno 1 Flashcards
(13 cards)
What are the three lines of defense in the immune system?
- Epithelial surfaces (skin, mucosa) as physical barriers
- Innate immune system (macrophages, neutrophils, NK cells, dendritic cells)
- Adaptive immune system (B cells and T cells)
What is the role of the innate immune system?
Provides immediate, non-specific defense using cells like macrophages, dendritic cells, NK cells, and neutrophils. It recognizes pathogens via pattern recognition receptors (PRRs) and initiates inflammation.
Name the key cells involved in innate immunity and their functions.
- Polymorphonuclear leukocytes PMNs (neutrophils): Aggressive, short-lived, engulf debris, activate T cells
- Macrophages: M1 (pro-inflammatory), M2 (anti-inflammatory)
- NK cells: Kill cells with low MHC-I via perforin/granzymes (via effector cells)
- Dendritic cells: Antigen-presenting, activate naive T cells
How do epithelial barriers defend against pathogens?
Skin forms a waterproof barrier (stratum corneum with keratin);
mucosal surfaces use mucus (e.g., mucociliary escalator in airway) to trap and remove pathogens. Damaged epithelial cells release pro-inflammatory cytokines.
What do T cells do in the immune response?
T helper cells (Th) assist other immune cells
Cytotoxic T lymphocytes (CTL) kill infected cells
T regulatory cells (Tregs) suppress immune response to prevent tissue damage
T cells recognize antigens presented by MHC on APCs.
What are Pattern Recognition Receptors (PRRs) and what do they detect?
PRRs detect Pathogen-Associated Molecular Patterns (PAMPs). Examples include:
- Cytoplasmic: NOD1, NOD2
- Membrane-bound: Toll-like receptors (e.g., TLR4 for LPS)
They activate NF-kB to trigger cytokine production and inflammation.
Describe the signaling pathway activated by TLR4 in response to LPS.
- LPS binds to TLR4 on dendritic cell
- TLR4 recruits adaptor proteins (Mal)
- Activates NF-kB transcription factor
- NF-kB enters nucleus and promotes expression of cytokines (e.g., IL-1, TNF-α, IL-6, IL-8, IL-12)
What cytokines are produced following TLR4 activation and what are their functions?
IL-1 and TNF-α: Promote inflammation
IL-8: Attracts neutrophils
IL-6: Stimulates B cells
IL-12: Activates T cells
How do NK cells distinguish between healthy and abnormal cells?
NK cells use activating and inhibitory receptors. Inhibitory receptors detect MHC-I on healthy cells and suppress killing. If MHC-I is missing (e.g., in tumor or virally-infected cells), activation dominates and NK cells release cytotoxins.
What are chemokines and what do they do?
Chemokines are peptides that attract immune cells by creating a chemical gradient. They guide cells like leukocytes to sites of infection (via leading edge) through chemotaxis. Subfamilies: CXC, CC, CX3C, C.
What is the complement system and what are its functions?
A group of 30 proteins in plasma that support innate immunity. Functions:
1. Opsonization (coated with molecules that help recognition) (C3b)
2. Cell lysis (via membrane attack complex)
3. Promote inflammation
4. Enhance phagocytosis
What are the three pathways of complement activation?
- Classical pathway: Activated by antibody-antigen complexes
- Alternative pathway: Activated by microbial surfaces
- Lectin pathway: Triggered by mannose-binding lectin
Why is C3 protein important in complement?
C3 is the most abundant complement protein. Its cleavage products (C3a, C3b) drive opsonization, inflammation, and formation of the membrane attack complex for cell lysis.
