Immune System Quiz: Innate Immunity Basics

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Questions and Answers

What is the primary function of the immune system?

To recognize and neutralize foreign and aggressive structures (correct)

To provide energy to the body during infections

To regulate body temperature during illness

To produce antibodies against all foreign substances

Which of the following is NOT a characteristic of the innate immune system?

Acts immediately after exposure

No immunologic memory

Specific to particular pathogens (correct)

Present from birth

How quickly is the innate immune system activated after pathogen exposure?

Within 20-30 minutes (correct)

Only after several days

Within seconds

After a few hours

What role do pattern-recognition receptors (PRRs) play in the immune response?

They recognize microbial patterns and interact with them Signup and view all the answers

Which cells are specifically recruited first to sites of inflammation?

Neutrophils Signup and view all the answers

What is one method by which neutrophils can neutralize invading microbes?

Phagocytosis and forming neutrophil extracellular traps (NETs) Signup and view all the answers

What do pathogen-associated molecular patterns (PAMPs) include?

Bacterial lipopolysaccharides and viral DNA/RNA Signup and view all the answers

Which of the following components is NOT part of the innate immune system?

Memory B cells Signup and view all the answers

What is the main function of the Lectin pathway in the complement activation process?

Initiates the formation of the membrane attack complex Signup and view all the answers

Which cytokine is primarily associated with the activation of endothelial cells and synthesis of acute phase proteins?

Interleukin 1 (IL-1) Signup and view all the answers

What characteristic do NK cells lack that distinguishes them from T and B lymphocytes?

Antigenic specificity Signup and view all the answers

Which part of the spleen is responsible for the phagocytosis of senescent erythrocytes?

Red pulp Signup and view all the answers

How do antibodies mediate tumor and viral cell destruction?

Through antibody-dependent cellular cytotoxicity (ADCC) Signup and view all the answers

Which characteristic of the adaptive immune system allows for a stronger response upon subsequent exposures to the same antigen?

Memory Signup and view all the answers

Which lymphoid organ is primarily involved in T cell maturation?

Thymus Signup and view all the answers

What type of immunity is achieved through serotherapy?

Passive immunity Signup and view all the answers

Which of the following describes the function of Fc receptors on NK cells?

Triggering antibody-dependent cellular cytotoxicity (ADCC) Signup and view all the answers

What characterizes peripheral lymphoid organs?

They facilitate mature lymphocyte interactions. Signup and view all the answers

What is the primary function of macrophages as antigen presenting cells (APCs)?

Capture, processing, and presenting antigens to lymphocytes Signup and view all the answers

Which of the following cytokines is released by macrophages to regulate cellular function?

TNF-α Signup and view all the answers

What is one of the biological functions of the complement system?

Chemotaxis and activation of neutrophils Signup and view all the answers

Which component of the complement system is responsible for initiating the classical pathway?

IgG1 Signup and view all the answers

Which of the following is NOT a secretion product of macrophages?

Immunoglobulins Signup and view all the answers

During inflammation, which component significantly increases vascular permeability?

Histamine Signup and view all the answers

What role do anaphylatoxins like C5a and C3a play in the immune response?

Stimulating chemotaxis and mast cell activation Signup and view all the answers

Which of the following correctly describes the lifespan of monocytes in circulation?

8-12 hours Signup and view all the answers

Which cytokine is primarily associated with osteoclast activity in rheumatoid arthritis?

IL-1 Signup and view all the answers

What role does IL-17 play in the context of rheumatoid arthritis?

It promotes inflammation and joint destruction. Signup and view all the answers

Which cell type is primarily involved in the synthesis of autoantibodies in rheumatoid arthritis?

B cells Signup and view all the answers

Which type of T-helper cells is particularly associated with the production of IL-17?

TH17 Signup and view all the answers

Which cytokine is known to suppress the immune response in rheumatoid arthritis?

IL-10 Signup and view all the answers

What is the function of TGF-β in rheumatoid arthritis?

Regulates immune responses towards anti-inflammatory actions. Signup and view all the answers

Which cytokine is critically involved in the amplification of the inflammatory response in rheumatoid arthritis?

IL-1 Signup and view all the answers

Which of the following cytokines is predominantly secreted by macrophages in rheumatoid arthritis?

IL-6 Signup and view all the answers

Which type of lymphoid tissue is primarily associated with the gut?

GALT Signup and view all the answers

What is the lifespan of T cells compared to B cells?

T cells live longer than B cells. Signup and view all the answers

What type of antigen is known for its ability to suppress immune mechanisms?

Tolerogen Signup and view all the answers

What are the receptors found on B cells primarily responsible for recognizing antigens?

BCR and Fc receptors Signup and view all the answers

Which type of antigen is derived from the same individual?

Autologous antigen Signup and view all the answers

Which class of MHC molecule binds to CD4 T cells?

MHC II Signup and view all the answers

What is the primary function of the paratope in antibodies?

To complement the epitope structure Signup and view all the answers

What distinguishes a complete antigen from an incomplete antigen?

Incomplete antigens require a carrier to elicit an immune response. Signup and view all the answers

Which type of immunoglobulin is primarily associated with mucosal immunity?

IgA Signup and view all the answers

What role do cytokines like IL-2 and IFN-γ play in the immune response?

They enhance macrophage activation and T cell responses. Signup and view all the answers

Study Notes

Introduction to Immunity and the Immune System

Immunity is the body's defense mechanism against foreign and harmful substances.
The immune response is triggered by the entry of an antigen into the body.
The immune system comprises cells and soluble factors that work together to protect the host from pathogens.
The immune system distinguishes between self and non-self structures through innate and adaptive mechanisms.

Innate Immune System

The innate immune system (IIS) is present from birth, genetically determined, and the first line of defense against aggressions.
It acts immediately (20-30 minutes after exposure to a pathogen).
It controls the replication of invading pathogens rapidly.
The IIS acts nonspecifically, has identical behavior with repeated exposure, and lacks immunologic memory.

Components of Innate Immunity

Mechanical barriers: skin, mucosa, tears, saliva, acid pH, temperature, and oxygen.
Humoral factors: complement, acute phase reactants, and cytokines.
Phagocytic cells: myelomonocytic lineage, and neutrophils.
Lymphocytes of innate immunity: NK cells and ILCs.

Activation of the Innate Immune System (IIS)

Pattern recognition receptors (PRR): TLRs (Toll-like receptors) recognize and interact with motifs specific to microbes, viruses, and damaged tissues.
PAMPs (pathogen-associated molecular patterns): bacterial LPSA, mannans, flagellin, and viral DNA/RNA.
DAMPs (damage-associated molecular patterns): alarmins, constitutively available molecules passively released from necrotic cells, including HMGB1, HSP 60, 70, and antimicrobial peptides.

Neutrophils

First cells recruited to inflammation sites by various chemotactic signals.
Neutralize invading microbes through:
- Phagocytosis: engulfing the microbe with intracellular granules containing peptides, proteases, and highly reactive oxidizing agents.
- Neutrophil extracellular traps (NETs): release of granules, proteins, and histones bound to a DNA and histone mesh-like structure that kills microbes independent of phagocytosis.

The Mononuclear-Phagocytic System (MPS)

Composed of monocytes and macrophages.
Cells from the same medullary lineage, have similar morphology (mononuclear cells), and function (phagocytosis).

Monocytes

1–8% of white blood cells (WBC).
Diameter of 10–15 µm.
Half-life of 8–12 hours.

Macrophages (Mf)

Diameter of 10–25 µm.
Contain lysosomal granules.
Activated by cytokines (IFN-γ), antigens, and mitogens.
Act as antigen-presenting cells (APCs) and effector cells.

Macrophage Surface Receptors:

Immune receptors: Fc receptors for IgG (FcγR I, II, III), IgE (FcεR), complement receptors (CR1, CR3, CR4), and adhesion molecules.
Nonimmune receptors: glycoproteins from bacterial surfaces, denatured proteins, fibronectin, tumor antigens, and hormones.

Macrophage Secretion Products

Factors of cellular differentiation: CSFs.
Regulators of cellular function: IL-1, IL-8, TNF-α, IFN-γ, and PDGF.
Hydrolytic enzymes: collagenase, lipase, and elastase.
Complement components: C1–C5, B, and D.
Coagulation factors: tissue thromboplastin, FV, VII, IX, and X.
Plasmatic proteins: α2-macroglobulin, α1-antitrypsin, and fibronectin.
Reactive oxygen metabolites: O3, H2O2, and HO-.
Arachidonic acid metabolites: PGE2, LTC4, and TxB2.
Nitric oxide (NO):

Antigen-Presenting Cells (APCs)

Capture, process, and present antigens to lymphocytes.
Release activating cytokines.
Examples: Macrophages, Dendritic cells (DC), B lymphocytes, and other cells.

Complement System

Functions:
- Inflammation: activation of neutrophils, macrophages, chemotaxis, mast cell degranulation, increased vascular permeability, smooth muscle contraction.
- Cell lysis: destruction of cells.
- Viral neutralization: disables viruses.
- Opsonization: coating the surface of a target (e.g., bacteria).
- Clearance of immune complexes: removing antigen-antibody complexes.

Complement Activation Pathways

Classical pathway: triggered by antigen-antibody complexes (IgG1, IgG3, IgM), antigens, viruses, and endotoxins.
Alternative pathway: triggered by bacterial components, aggregated IgA, IgG4, polysaccharides, and enzymes.
Lectin pathway: initiated by mannan-binding lectin (MBL) which belongs to the same family as C1q. This pathway involves MBL-associated serine proteases (MASP-1 and MASP-2), similar in function to C1r and C1s.

MAC (Membrane Attack Complex)

A complex formed during the complement activation cascade that creates pores in cell membranes, ultimately leading to cell lysis.

Cytokines

Examples: TNF-α, IL-1, IL-6, and IL-17.
Functions: pro-inflammatory, activation of neutrophils and endothelial cells, fever, synthesis of acute phase proteins, and various roles in specific diseases.
Disease associations: Rheumatoid arthritis, Ankylosing spondylitis (AS), Crohn Disease, Gout, Mediterranean fever, vasculitis.

NK Lymphocytes

Large granular lymphocytes present from birth.
Derive from a lineage different from T and B cells.
Account for 5–10% of the circulating lymphocyte population.
Characteristic surface molecules: CD16 and CD56.
Found in blood, spleen, pulmonary interstitial area, bowel, liver.
Receptors for Fc IgG1 and IgG3: participate in antibody-dependent cell-mediated cytotoxicity (ADCC).
Secrete cytokines.
Lack MHC (Major Histocompatibility Complex) restriction.
Lack antigenic specificity.
Lack immunologic memory.

NK Cell Functions

Cytotoxic for tumor cells and virally infected cells via ADCC.
Enhance macrophage phagocytic capacity.

Adaptive Immune System (AIS)

Comprises T and B lymphocytes.
Immunizing events:
- Natural: Passive (through the placenta) and active (during convalescence).
- Artificial: Passive (serotherapy - antitoxins) and active (vaccination).

Characteristics of Adaptive Immunity

Specificity: Recognizes and targets specific antigens.
Diversity: Generates a wide range of receptors for diverse antigens.
Memory: Remembers prior exposures and mounts more rapid and robust responses upon re-encounter.
Specialization: Different cells perform specific functions.
Autolimitation: Controlled response that terminates when the threat is neutralized.
Non-reactivity to self: Does not attack the body's own tissues.

Lymphoid System

Central lymphoid organs: Bone marrow and thymus.
Peripheral lymphoid organs:
- Capsulated organs: Spleen and lymph nodes.
- Diffuse lymphoid tissue: GALT (gut-associated lymphoid tissue), BALT (bronchial-associated lymphoid tissue), and SALT (skin-associated lymphoid tissue).

Bone Marrow

Site of hematopoiesis (blood cell production).
Produces all blood cells, including lymphocytes.

Lymphocyte Differentiation

T lymphocytes mature in the thymus.
B lymphocytes mature in the bone marrow.

Thymus

Essential for T cell maturation and development.

Spleen

Two parts:
- Red pulp: Contains macrophages for the phagocytosis of senescent erythrocytes.
- White pulp: Contains lymphocytes organized in areas called Periarteriolar Lymphoid Sheath (PALS).
  - Periarteriolar area: T cells (thymodependent area).
  - Peripheral zone of PALS: B cells (thymoindependent area).

Lymph Node

Filters lymph (fluid circulating through lymphatic vessels).
Site of antigen presentation and immune responses.
Three areas:
- B-dependent area (cortex): Contains B lymphocytes, lymphoid follicles, and plasma cells (germinal centers).
- T-dependent area (paracortex): Contains T lymphocytes.
- Medulla: Contains blood and lymphatic vessels, T lymphocytes, B lymphocytes, plasma cells, macrophages, and dendritic cells.

Diffuse Lymphoid Tissue

GALT: Gut-associated lymphoid tissue, includes Waldeyer's lymphatic ring, palatine, pharyngeal, and lingual tonsils, Peyer's patches, and appendix.
BALT: Bronchial-associated lymphoid tissue.
SALT: Skin-associated lymphoid tissue.

T Cells

60–80% of total lymphocytes.
Long lifespan (months to years).
Surface receptors: TCR-CD3, CD2, CD4 (helper T cells), CD8 (cytotoxic T cells), CD28, and LFA-1 (CD11a).

B Cells

5–10% of total lymphocytes.
Short lifespan (days).
Surface receptors: B cell receptor (BCR), Fc receptors for IgG (FcγRI, II, III), complement receptor CD35 for C3b, MHC I and II, CD5, CD19, CD20, CD10 (CALLA), CD21 (for Epstein-Barr virus), LFA-1, and L-selectin.

Antigens (Antibody Generators)

Molecules that induce an immune response and react with its products (activated T cells or antibodies (Ab) - Ig).
Important distinctions:
- Immunogen: Induces an immune response.
- Tolerogen: Induces suppressor mechanisms.
- Autoantigen/tumor antigen: Endogenous antigens recognized by the immune system in autoimmune disorders or cancer.

Antigenic Determinants (Epitopes)

Linear: Consecutive amino acids.
Conformational: Three-dimensional structure.
Valency: Number of epitopes on a molecule.

Paratope

The structure of the antibody that binds to the epitope.

Classification of Antigens

Structural criteria:
- Complete: Can induce an immune response independently.
- Incomplete (haptens): Require carrier molecules to elicit an immune response.
Chemical criteria:
- Proteins: Common antigens.
- Glycoproteins: Blood types A, B, and Rh antigens.
- Small peptides: Insulin, growth hormone.
- Polysaccharides: Bacterial capsules.
- Nucleic acids: Viral DNA and RNA.
- Lipids: Mycobacterial lipids.

Antigen Types

Autologous antigens: From the same person.
Syngeneic antigens: Genetically identical, such as twins or clones.
Alloantigens: Present in some members of a species, like blood group antigens.
Xenoantigens: From another species, intensely immunogenic.
Heterophile antigens: Common to different species.
Organ/tissue-specific antigens: Present in specific organs or tissues.
Sequestred antigens: Hidden from the immune system until exposed (e.g., during tissue damage), potentially triggering autoimmune reactions.

MHC (Major Histocompatibility Complex) = HLA (Human Leukocyte Antigen)

A set of genes that code for proteins involved in immune recognition.
Regions:
- Class I: Expressed on all nucleated cells.
- Class II: Expressed on immune cells involved in antigen presentation.
- Class III: Contains genes for complement components and other immune-related proteins.

MHC I

Location: All nucleated cells.
Binds: CD8+ cytotoxic T cells.
Presents: Endogenous antigens (synthesized within the cell, like viral proteins).
Functions:
- Graft rejection: Recognizes and attacks cells from different individuals.
- Cellular immune response: Activates cytotoxic T cells to destroy infected or altered cells.

MHC II

Location: Cells involved in immune responses (APCs like macrophages, B lymphocytes, dendritic cells).
Binds: CD4+ helper T cells.
Presents: Exogenous antigens (taken up by cells from outside).
Functions:
- Cooperation with T cells: Activates helper T cells to initiate immune responses.
- Minor role in graft rejection: Can contribute to rejection but to a lesser extent than MHC I.

Antigen Processing

Breaking down antigens into smaller peptides that can be presented by MHC molecules.

Antigen Recognition

The process by which the immune system identifies and binds to specific antigens.

T Cell Activation

Requires two signals:
- Signal 1: Ag recognition by the TCR (T cell receptor)-MHC complex.
- Signal 2: Costimulation by the interaction of CD28 on T cells with B7 molecules (CD80/CD86) on antigen-presenting cells.
Results in:
- Production of IL-2: A growth factor that stimulates clonal expansion (multiplication) of activated T cells.

Immune Activation

Activated T cells release cytokines: IL-2, IL-4, IFN-γ, and TNF-α.
Triggers various immune responses:
- Macrophage activation: Enhanced phagocytic and microbicidal activity.
- LT CD8 activation: Induction of cytotoxic T cell activity.
- LB activation: Stimulation of antibody production by B cells.

Antibody Secretion

Activated B cells differentiate into plasma cells, which secrete antibodies.

Immunoglobulins (Ig)

Description: Glycoproteins synthesized by activated B cells (plasma cells).
Location: Associated with cell membranes or circulating in body fluids: serum, extravascular fluids, and lymphoid tissue.
Serum concentration: 20% of plasmatic proteins.
Structure: Monomeric structure containing two identical heavy chains (H) and two identical light chains (L):
- Heavy chains:
  - IgG (γ): Most abundant in serum, crosses the placenta, activates complement, binds to Fc receptors on phagocytes. Five subtypes (IgG1, IgG2, IgG3, IgG4).
  - IgA (α): Found in secretions (mucous membranes), protects against mucosal pathogens. Two subtypes (IgA1, IgA2).
  - IgM (μ): First antibody produced during an immune response, activates complement, good at agglutinating antigens.
  - IgD (δ): Functions as a B cell receptor.
  - IgE (ε): Important in allergic reactions and parasitic infections, binds to Fc receptors on mast cells and basophils.
- Light chains: Kappa (K) or lambda (λ). Only one type of light chain present in each immunoglobulin molecule.

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