Immune System 101
Define the immune system and its primary functions (3).
DEFENSE - against pathogens
SURVEILLANCE - identifying and eliminating abnormal cells
HOMEOSTASIS - removing dead/damaged cells
How does the immune system find antigens?
Continuous recirculation of naive lymphocytes through the peripheral lymphoid organs to which antigen is carried from any side of infection.
Explain how the membrane attack complex kills microbes
Lysis of the microorganism (perforation of the membrane).
What do cytokines do? Where do they travel? Give an example of a cytokine.
Proinflammatory cytokines produced by sentinel cells induce local acute inflammatory responses and also can travel in the blood and lymph to distant sites. Creating effects on other organs that help to fight infection (hypothalamus --> fever, liver --> protein production, bone marrow --> WBCs). Examples: TNF, IL-1, IL-6.
Draw out the general structure of an antibody.
Make sure to include the following features: light chain, heavy chain, constant regions, variable regions, fab region, fc region, hinge region, antigen binding region
Give an example of active and passive immunity.
Active: Immunity acquired by receiving antibodies from another source - ex: maternal antibodies.
Passive: Immunity acquired by the body's own immune response to antigen exposure - ex. vaccination, getting sick.
List the primary lymphoid organs and the secondary lymphoid organs and their functions
Primary lymphoid organs: Bone marrow (hematopoiesis, B-cell maturation), thymus (T-cell maturation)
Secondary lymphoid organs: Lymph nodes --> filter antigen from lymph, site of response/proliferation of T and B cells. Spleen --> filters antigens from blood, stores and filters RBCs. MALT, GALT, BALT.
Indicate which complement proteins are pro-inflammatory.
C3a and C5a
Describe the activation and the function of the natural killer cells.
Activation - Receptors detect stress ligands or antibody-coated cells.
Cytotoxic killing - Release perforin (forms pores) and granzymes → kill virus-infected or cancer cells.
Cytokine production - Secrete IFN-γ to activate macrophages and enhance Th1 immune responses.
Immune surveillance - Patrol tissues, detect abnormal cells (tumors, virus-infected).
What are the 3 functions of antibodies?
Opsonization - tags bacteria for phagocytosis by macrophage
Neutralization - binds to toxin and then complex is ingested by macrophage
Complement activation - classical pathway only
Describe the major components of the immune system (Organs (5), Cells (7 types), and Molecules (4)).
Organs - Primary: Bone marrow and thymus. Secondary: Lymph nodes, spleen, MALT
Cells - WBCS: Neutrophils, lymphocytes, macrophages, dendritic cells, eosinophils, basophils, mast cells
Molecules - Cytokines, complement proteins, antibodies, acute phase proteins
Differentiate between innate and adaptive immunity.
Innate: Fast, non-specific, defense mechanisms present from birth. Examples: skin, mucous membranes, macrophages, neutrophils, NK cells, complement, acute phase proteins.
Adaptive: Slow, specific, has memory (antibodies), develops after exposure to antigens.
Name one way that complement is regulated
DAF, MCP, and CR1 - Act on C3/C5 convertases
Factor H - works on the alternative pathway by inhibiting Factor B
Proteins that inhibit MAC
What is the clonal selection theory? What happens if clonal selection effs up?
The removal of potentially self reactive immature lymphocytes by clonal deletion. No clonal deletion increases risk of self reactive lymphocytes --> autoimmunity.
Describe the structures of IgM, IgG, IgA, and IgE isotype antibodies. List the Characteristics of the different Ig classes.
IgM – first produced, good at complement activation, 5 antigen binding sites
IgG – most abundant, long-term immunity, crosses placenta (species dependent), 1 antigen binding sites
IgA – mucosal immunity, 2 antigen binding sites
IgE – allergy, parasites, binds mast cells/basophils, 1 antigen binding sites
Describe the function of the following WBCs: Neutrophils, Eosinophils, Basophils, Macrophages, Mast Cells, Natural Killer Cell, Dendritic Cells, B Cells, Helper T Cells, Cytotoxic T Cells
Neutrophils - Phagocytosis
Eosinophils - Involved in allergic and parasitic infections
Basophils - Involved in allergic responses and release histamine
Macrophages - APC, phagocytosis
Dendritic Cells - APC
Mast Cells - Release histamine
Natural Killer Cell - Lysis of infected cells
B Cells - Transform into plasma cells and secrete antibodies
Helper T Cells - Stimulate B cells to make antibodies, activate macrophages.
Cytotoxic T Cells - Kill infected cells by inducing apoptosis
Name the components of humoral immunity, both innate and adaptive. Name the components of cell-mediated immunity, both innate and adaptive. Describe the mechanism of each defense level
Humoral Immunity - Innate: Complement proteins, and acute phase proteins. Adaptive: Antibodies
Cell Mediated - Innate: Macrophages, neutrophils, monocytes, mast cells, basophils, Eosinophils, dendritic cells, and Natural killer cells. Adaptive: T and B lymphocytes.
In general terms, what is complement and what does it do (3 outcomes)?
Complement is a cascade of proteins (C1-C9). Initial activation is due to presence of foreign molecules. Opsonization (coating of the pathogen) by C4b and C3b. Chemoattraction of accessory cells.
Lysis of target cells by MAC.
Describe functions of macrophages. Include its function in pro inflammatory and anti inflammatory processes.
Phagocytosis of microbes, dead cells, debris. Clears dead neutrophils and debris → prevents ongoing inflammation.
Antigen presentation - Process antigens & present via MHC II to activate T cells.
Cytokine secretion (pro-inflammatory) - Release TNF-α, IL-1, IL-6 to recruit and activate immune cells.
Bridge innate & adaptive immunity - Recruit/activate lymphocytes, NK cells, neutrophils.
Secretion of anti-inflammatory cytokines (IL-10, TGF-β), Suppresses further immune activation; shifts environment toward healing.
Production of growth factors (VEGF, PDGF, FGF). Stimulates angiogenesis (new blood vessel growth) and fibroblast activity.
Psych! This question is not about antibodies. What are sentinel cells? Name examples.
Their main role is to detect danger (pathogens or injury) and alert the immune system quickly. Examples include: Macrophages, dendritic cells, and mast cells. They detect danger by recognizing PAMPS. They activate other immune cells and initiate adaptive immunity as APCs.
Describe the difference between the following immunology terms: Antigen, Antibody, Pathogen, Immunogen, Epitope
Antigen: Any substance recognized by the immune system as foreign, capable of triggering an immune response.
Antibody: A protein produces by B cells that binds specifically to an antigen to neutralize or detroy it.
Pathogen: A microorganism capable of causing disease.
Immunogen: A substance capable of inducing an immune response.
Epitope: A specific part of the antigen recognized by an antibody or t cell receptor.
List the three lines of immunological defense and their hierarchy order in which they function (first line of defense, second line of defense, third). Describe the mechanism of each defense level.
1st Line (barriers): prevent microbial entry/attachment - intact skin and constant shedding of surface skin cells; normal flora; mucus that covers the respiratory, gastrointestinal, reproductive and urinary epithelia; turbulent airflow in nasal passages and cilia in respiratory airways, intermittent flow in the GI and urinary tracts; and the acid pH of the stomach.
If the first defense is overcome...
2nd Line (cells/proteins): Rapid recognition & attack - Orchestrated by inflammation and release of cells/molecules such as: macrophages, neutrophils, NK cells, complement, acute phase proteins, cytokines.
If the second defense is overcome...
3rd Line: Specific recognition - Adaptive immune responses (B & T lymphocytes, antibodies, memory cells).
What are the 3 complement activation pathways and how are they different?
CLASSICAL PATHWAY: Adaptive Immunity, Antigen-antibody complexes activate C1qrs.
• MBLECTIN PATHWAY: Innate Immunity, lectin binding to pathogen surfaces activates MASP 2 protein.
• ALTERNATIVE PATHWAY: Innate Immunity, Pathogen surfaces cause spontaneous hydrolysis of C3.
Describe the cells and molecules involved in acute
inflammation. How does acute inflammation work?
Infectious agents exhibit PAMPs found on their surface. Sentinel cells (such as dendritic, macrophages, and mast cells) have PAMP receptors called toll-like receptors. When PAMP receptors engage PAMPS, they secrete cytokines that cause local capillaries to dilate, increases blood flow, allowing proteins and phagocytic cells to enter the area. This causes redness, heat, swelling, and pain. It also targets humoral components from plasms such as complement, antibodies, opsonizing agents, and cell mediated innate components.
Explain the results of naïve B-cell activation with and without T-cell help.
B cell activation signal can be delivered by the antigen itself or by non-thymus-derived accessory cells.
T independent - B cell activation can be delivered by the antigen itself
T dependent - Needs Helper 2 T cells to recognize peptides displayed on MHC II on the B cell