Immunobiology Flashcards (Lecture 1-8)
innate immune system
consists of complement, granulocytes, NK cells, antigen presenting cells
Adaptive (specific) immune system
B cells, T cells, to antibodies
Immune system organs- primary lymphoid organs
Bone marrow, thymus
Basophyls
Similar to mast cells but found in blood.Release inflammatory mediators (histamine, cytokines).
Support adaptive immunity, particularly antibody responses.
Neutorphyls
Most abundant white blood cells.
First responders to infections.
Short-lived but potent:
- Phagocytose microbes.
- Secrete cytokines.
- Form Neutrophil Extracellular Traps (NETs) to trap bacteria.
Monocytes/Macrophages
Monocytes in blood migrate to tissues to become macrophages.
Functions:
- Phagocytosis (engulfing pathogens).
- Cytokine secretion.
- Antigen presentation to T cells.
Antigen Presenting Cells
Capture and present antigens to T cells.
Types:
- Macrophages.
- Dendritic cells.
- B cells.
Immune system organs- Secondary lymphoid organs
Spleen, lymph nodes, peyer’s patches, appendix, tonsils and adenoids
Inflammatory mediators
Increased blood flow causes increased capillary permeability, attracts cells, alerts immune system, clotting.
Innate immune response to cuts
Mast cells secrete histamine that cause nearby capillaries to dilate. Neutrophils and monocytes leave capillaries. Antigen presenting cells, Etc. I missed the rest of the tutorial slide
What are Eosinophils
Attack parasites and helminths. Derived from myeloid progenitors in bone marrow.
Contain granules with enzymes that:
- Attack parasites and helminths.
- Can also damage host tissue.
Increase during inflammation and allergic responses.
Natural Killer (NK) Cells
Target and destroy infected or cancerous cells. Recognize stressed cells lacking MHC-I. Release perforins and granzymes to induce cell death. AntiVIRAL immunity.
Dendritic Cells
Strategically positioned in tissues.Function: Detect pathogens and Present antigens to T cells in lymph nodes.
Cell morphology
Shape, size, and internal structures (microscopy).
Surface molecule expression
Using flow cytometry and CD markers.
CD Nomenclature (Cluster of Differentiation)
CD molecules help in classifying immune cells.
- CD1 to CD371 represent various immune markers.
- Groups of antibodies recognizing the same molecule form a “cluster”
Reside in epithelial tissues.Different types:
ILC1 (defense against viruses).
ILC2 (allergic inflammation).
ILC3 (gut barrier function).
ILC4 (form secondary lyphoid tissues)
ILC5 (Anticribrobia peptides, phaogcyte)
Myeloid Cells
Myeloid cells include:
- Phagocytes (neutrophils, monocytes/macrophages).
- Granulocytes (mast cells, eosinophils, basophils).
These cells originate from common myeloid progenitors.
Mast Cells
Immature mast cells migrate to tissues where they mature.
Reside in skin, lungs, gut (exposed to the environment).
Function:
- Release histamine and cytokines during allergic reactions.
- Long-lived cells.
What are the three main components of the immune system?
A: Epithelial barriers, immune cells, and immune molecules (cytokines, plasma proteins).
Innate immunity: Rapid, non-specific, no memory.
Adaptive immunity: Slower, highly specific, provides long-term memory.
What are the primary lymphoid organs and their function?
Bone marrow: Produces all blood cells, site of B-cell maturation.
Thymus: Site of T-cell maturation.
What are the secondary lymphoid organs, and what do they do?
Lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).
Function: Site where immune responses are initiated.
What is the main function of lymph nodes?
Filter lymph, trap pathogens, and activate lymphocytes.
What is the role of the spleen in immunity?
Filters blood, removes old RBCs, and traps bloodborne antigens.
What are phagocytes, and what is their function?
Cells that engulf and digest microbes, including neutrophils and macrophages.
Which innate immune cells release histamine and inflammatory mediators?
Mast cells, basophils, and eosinophils.
What are dendritic cells, and why are they important?
Antigen-presenting cells (APCs) that bridge innate and adaptive immunity by activating T cells.
What are natural killer (NK) cells, and what do they do?
Lymphocytes that kill virus-infected and cancerous cells by releasing perforins and granzymes.
What are B cells and T cells, and how do they differ?
B cells: Produce antibodies.
T cells: Direct cell-mediated immunity.
What are the five hallmarks of the innate immune system?
Rapid response (within hours).
Short duration (response fades quickly).
Repetitive response (same reaction every time).
Interacts with adaptive immunity.
Does not attack self (tolerance to host tissues).
How does the innate immune system recognize pathogens?
Through pattern recognition receptors (PRRs) that detect pathogen-associated molecular patterns (PAMPs).
What are PAMPs and DAMPs?
PAMPs (Pathogen-Associated Molecular Patterns) – Microbial molecules (e.g., LPS, viral RNA).
DAMPs (Damage-Associated Molecular Patterns) – Host molecules from injured or stressed cells.
What are Toll-Like Receptors (TLRs)?
Membrane-bound PRRs that recognize extracellular and endosomal pathogens.
Where are TLRs located?
Cell surface (detect extracellular microbes) and endosomes (detect viral RNA).
What signaling pathway is activated by TLR engagement?
The NF-κB pathway, which induces inflammatory cytokine expression.
What adaptor protein is used by most TLRs?
MyD88 (except for TLR3, which uses TRIF).
What are the steps of phagocytosis?
Recognition (microbe binds PRRs).
Engulfment (phagosome forms).
Fusion (phagosome + lysosome = phagolysosome).
Microbial killing (by ROS, NO, enzymes).
How do neutrophils kill microbes?
Through phagocytosis, release of reactive oxygen species (ROS), and Neutrophil Extracellular Traps (NETs), netosis.
What are antimicrobial peptides (AMPs), and how do they work?
Small proteins (e.g., defensins) that disrupt bacterial membranes, causing lysis.
What is the difference between alpha-defensins and beta-defensins?
Alpha-defensins: Produced by leukocytes and Paneth cells (gut).
Beta-defensins: Produced by epithelial cells (continuous secretion).
What are NOD-Like Receptors (NLRs), and where are they located?
Cytoplasmic PRRs that detect intracellular bacterial components and stress signals.
What are NOD1 and NOD2, and what do they recognize?
NOD1 → Recognizes Gram-negative bacteria (Meso-DAP).
NOD2 → Recognizes both Gram-negative & Gram-positive bacteria (MDP).
How does NOD receptor signaling work?
NOD receptors activate RIPK2, which triggers NF-κB to induce inflammation.
What is the function of DAMP recognition in innate immunity?
Detects host cell damage, triggering inflammation.
What is an example of a DAMP-recognizing receptor?
TLR9, which detects unsequestered host DNA as a danger signal.
What is the complement system?
A system of circulating and membrane-bound proteins that assist immune responses by:
- Opsonizing pathogens (C3b).
- Inducing inflammation (C3a, C5a).
- Forming Membrane Attack Complex (MAC) (C5b-C9).
What are the three pathways of complement activation?
- Alternative pathway: Direct activation by microbial surfaces (innate immunity).
- Classical pathway: Triggered by antigen-antibody complexes (adaptive immunity).
- Lectin pathway: Initiated by mannose-binding lectin (MBL) binding to microbial sugars.
What is C3 “tick-over” in the alternative pathway?
C3 undergoes spontaneous low-level hydrolysis to C3b.
If C3b binds a microbial surface, it initiates the alternative pathway.
If no microbe is present, C3b is quickly inactivated in the fluid phase.
What are the functions of C3a, C3b, C5a, and MAC?
C3a & C5a: Anaphylatoxins (cause inflammation, recruit immune cells).
C3b: Opsonization (coating pathogens for phagocytosis).
MAC (C5b-9): Pore-forming complex that lyses pathogens.
What diseases are associated with complement deficiencies?
C3 deficiency → Severe, recurrent pyogenic bacterial infections.
C2 deficiency → Autoimmune diseases (lupus-like symptoms).
C1 inhibitor (C1-INH) deficiency → Hereditary angioedema (excess inflammation, swelling).
DAF (Decay-Accelerating Factor) deficiency → Paroxysmal nocturnal hemoglobinuria (PNH) (uncontrolled complement activation on RBCs).
What is the role of MHC in immunity?
MHC molecules present peptide antigens to T cells.
MHC Class I → presents intracellular peptides to CD8+ cytotoxic T cells.
MHC Class II → presents extracellular peptides to CD4+ helper T cells.
How are antigens processed for MHC Class I vs. MHC Class II?
MHC I Pathway (Cytosolic Pathway):
- Proteasome degrades intracellular proteins.
- Peptides are transported into the ER via TAP (Transporter Associated with Antigen Processing).
- Loaded onto MHC I and transported to the cell surface.
MHC II Pathway (Endocytic Pathway):
- Antigens are phagocytosed and degraded in endosomes/lysosomes.
- Invariant chain (Ii) blocks premature peptide binding in the ER.
- HLA-DM removes CLIP, allowing antigenic peptides to load onto MHC II.
What is cross-presentation and why is it important?
Cross-presentation: APCs can present extracellular antigens on MHC I to activate CD8+ T cells.
Importance: Allows DCs to stimulate cytotoxic T cell responses against viruses and tumors, even if they don’t infect APCs directly.
What is MHC polymorphism and why is it significant?
MHC genes are highly polymorphic, meaning many alleles exist within the population.
Ensures diversity in antigen presentation and prevents pathogen escape.
What are the functions of B cells?
Produce antibodies for humoral immunity.
Differentiate into plasma cells (secrete antibodies) or memory B cells (long-term immunity).
What are the key structural features of an antibody?
2 heavy chains + 2 light chains (Y-shaped structure).
Fab region (binds antigen) and Fc region (binds receptors for effector functions).
What are the 5 antibody isotypes and their roles?
IgM- First antibody produced, strong complement activation.
IgG- Most abundant, neutralization, opsonization, ADCC.
IgA- Mucosal immunity, protects gut & respiratory tract.
IgE- Binds mast cells → involved in allergies & helminth defense.
IgD- Functions in B cell development.
What is somatic hypermutation and affinity maturation?
Somatic hypermutation: B cells undergo mutations in the variable region to increase antibody affinity.
Affinity maturation: Selection for higher-affinity B cells in germinal centers.
What is class switching and why is it important?
Class switching: B cells change antibody isotype (IgM → IgG, IgA, etc.).
Does not change antigen specificity.
Requires T cell help (CD40-CD40L interaction).
What are the two main types of T cells and their functions?
CD8+ Cytotoxic T Cells: Kill virus-infected or cancerous cells.
CD4+ Helper T Cells: Activate macrophages, B cells, and other immune cells.
How do T cells recognize antigens?
T Cell Receptors (TCRs) bind peptide-MHC complexes.
CD4+ T cells → Recognize MHC Class II.
CD8+ T cells → Recognize MHC Class I.
How are TCRs generated?
V(D)J recombination generates TCR diversity.
Junctional diversity (nucleotide additions) increases specificity.
What are the stages of T cell selection in the thymus?
Positive Selection (Cortex):
- Ensures T cells recognize self-MHC.
- Cells that fail → die by neglect.
Negative Selection (Medulla):
- Removes self-reactive T cells.
- Prevents autoimmunity.
What are the major T cell subsets and their roles?
Th1- Activates macrophages, fights intracellular pathogens.
Th2- Helps B cells, fights helminths, mediates allergic reactions.
Th17- Enhances neutrophil response, protects barrier tissues.
Treg- Suppresses immune responses, prevents autoimmunity.
