Immunology: Innate and Adaptive Immunity

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Questions and Answers

Which type of immunity is characterized by components that are present before infection?

Innate immunity (correct)

Acquired immunity

Specific immunity

Adaptive immunity

Which cells are primarily responsible for cellular immunity?

B lymphocytes

Neutrophils

T lymphocytes (correct)

Natural killer cells

What is the approximate ratio of CD4 to CD8 T lymphocytes in circulation?

4:1

1:1

1:2

2:1 (correct)

What is the primary function of CD8+ T cells?

Kill infected or cancerous cells Signup and view all the answers

What does the CD4 molecule specifically bind to on antigen presenting cells?

Class II MHC molecules Signup and view all the answers

Which cytokines are produced specifically by TH1 cells?

IL-2 and interferon-γ Signup and view all the answers

Which molecule do T cells interact with, alongside CD28, for complete activation?

CD80 or CD86 Signup and view all the answers

What characterizes the immediate phase of a Type I hypersensitivity reaction?

Vasodilation and exudation from released vasoactive amines Signup and view all the answers

What type of receptors does a T lymphocyte express that is essential for its function?

T cell receptor (TCR) Signup and view all the answers

Which immunoglobulin constitutes the majority of plasma immunoglobulins after B-cell activation?

IgG Signup and view all the answers

What is the role of CD21 on B cells?

Functions as a complement receptor Signup and view all the answers

Which type of immunity is specifically responsible for defense against extracellular microbes?

Humoral immunity Signup and view all the answers

Which mechanism does NOT play a role in Type II hypersensitivity reactions?

Complement fixation and cytokine release Signup and view all the answers

Which of the following conditions is an example of a Type III hypersensitivity reaction?

Systemic lupus erythematosus Signup and view all the answers

Which of the following roles is NOT performed by macrophages?

Directly kill tumor cells through cytokines Signup and view all the answers

Which protein complex is linked to the T cell receptor and is involved in signal transduction?

CD3 complex Signup and view all the answers

What type of microbes are recognized by adaptive immune mechanisms?

All types of microbes including nonmicrobial substances Signup and view all the answers

What type of immune cells are primarily involved in Type IV hypersensitivity reactions?

CD4+ T cells and CD8+ T cells Signup and view all the answers

What distinguishes follicular dendritic cells from other dendritic cells?

Trapping of antibodies on cell surfaces Signup and view all the answers

What component of innate immunity blocks the entry of environmental microbes?

Epithelial barriers Signup and view all the answers

What happens to T cells that do not receive the second signal required for activation?

They undergo apoptosis or become anergic Signup and view all the answers

What is the outcome following the late phase of a Type I hypersensitivity reaction?

Leukocyte influx leading to prolonged inflammation Signup and view all the answers

Which class of antibody is present on the surface of all B cells?

IgM Signup and view all the answers

Which condition is associated with antibody-mediated cellular dysfunction in Type II hypersensitivity?

Myasthenia gravis Signup and view all the answers

Which type of hypersensitivity reaction mainly involves the formation of immune complexes?

Type III Signup and view all the answers

Where are dendritic cells primarily found?

In lymphoid tissue Signup and view all the answers

What do eosinophils primarily assist with in conjunction with TH2 cells?

Modulating allergic responses Signup and view all the answers

Which type of hypersensitivity reaction is primarily involved in graft rejection?

Type IV Signup and view all the answers

Which statement best describes the immune response in Type II hypersensitivity?

It features the destruction of cells with antibodies targeting surface antigens. Signup and view all the answers

Which immune process is primarily involved in Type IV hypersensitivity reactions?

Cytokine production from activated T cells Signup and view all the answers

What is the primary function of NK cells?

To kill tumor cells and virally-infected cells without sensitization Signup and view all the answers

Which of the following is NOT a feature of class I MHC molecules?

Primarily presents exogenous antigens Signup and view all the answers

Which cytokine is primarily secreted by NK cells?

IFN-γ Signup and view all the answers

How do activator receptors of NK cells function?

They identify ill-defined molecules Signup and view all the answers

What is the role of the CD8 molecule in relation to T cells?

It interacts with class I MHC-peptide complexes Signup and view all the answers

Class II MHC molecules are encoded in a region known as?

HLA-D Signup and view all the answers

Which of the following describes the receptors on NK cells?

Include both activator and inhibitor receptor types Signup and view all the answers

Which component is NOT a product of class III MHC genes?

Antigen-presenting glycoproteins Signup and view all the answers

What is the chromosomal location of the MHC genes?

Chromosome 6 Signup and view all the answers

What type of antigens can CD4+ helper T cells recognize?

Exogenous antigens presented by class II MHC Signup and view all the answers

Study Notes

Innate Immunity

The body's first line of defense against infection.
Present even before infection, and has evolved to specifically recognize microbes and protect against infections.
Components include epithelial barriers, phagocytic cells (neutrophils and macrophages), natural killer (NK) cells, and plasma proteins like those in the complement system.

Adaptive Immunity

Stimulated by microbes and can recognize non-microbial substances called antigens.
Divided into cell-mediated immunity (T lymphocytes) which defends against intracellular microbes, and humoral immunity (B lymphocytes and antibodies) which protects against extracellular microbes and their toxins.

T-Lymphocytes

Make up 60-70% of circulating lymphocytes.
Found in lymph nodes and spleen.
Each T-cell has a unique T cell receptor (TCR) composed of alpha and beta chains, with variable (antigen-binding) and constant regions.
TCR complex is linked to the CD3 complex involved in signal transduction.
CD4 and CD8 are expressed in two subsets of T lymphocytes, acting as coreceptors.
CD4 binds to class II MHC molecules on antigen-presenting cells.
CD8 binds to class I MHC molecules.
T-helper-1 (TH1) cells produce IL-2 and interferon-γ (IFN-γ), involved in delayed hypersensitivity, macrophage activation, and antibody production.
T-helper-2 (TH2) cells produce IL-4, IL-5, and IL-13, involved in activating eosinophils and other antibody production.
CD8+ T cells function as cytotoxic cells, killing other cells and secreting cytokines.

B-Lymphocytes

Constitute 10-20% of circulating lymphocytes.
Found in lymph nodes and spleen.
After antigen stimulation, transform into plasma cells and secrete immunoglobulins (IgG, IgM, IgA, IgE, and IgD).
Monomeric IgM is present on the surface of all B cells, forming an antigen receptor.
Somatic rearrangement of immunoglobulin genes results in unique antigen specificity.
Express other molecules, including CD19, CD20, CD21, and CD40.

Macrophages

Play several roles in the immune response.
Present antigens to T-cells through class II MHC molecules.
Produce cytokines that influence cells like T and B cells, endothelial cells, and fibroblasts.
Secrete toxic metabolites and proteolytic enzymes to lyse tumor cells.
Important effector cells in cell-mediated immunity and delayed hypersensitivity reactions.

Dendritic and Langerhan's cells

Have dendritic cytoplasmic processes and large amounts of class II MHC molecules.
Found in lymphoid tissue (dendritic) and the epidermis (Langerhan's).
Efficient antigen presenters with poor phagocytic activity.
Follicular dendritic cells contain antibodies on their cell surfaces, trapping antibodies via Fc receptors.

Natural Killer cells (NK cells)

Make up 10-15% of peripheral blood lymphocytes.
Don't express TCR or immunoglobulin.
Larger than small lymphocytes and contain azurophilic granules.
Part of the innate immune system, killing tumor cells and virally infected cells.
Express CD16 and CD56.
CD16 is an Fc receptor for IgG-coated cells, involved in antibody-dependent cell-mediated cytotoxicity.
Express activators (recognize ill-defined molecules) and inhibitors (recognize class I MHC).
Secrete IFN-γ.

Main Histocompatibility Complex (MHC)

MHC molecules bind peptide fragments of foreign proteins for presentation to T cells.
MHC genes are clustered on chromosome 6.
MHC gene products are categorized into class I, class II, and class III.
Class I MHC molecules are expressed on all nucleated cells and platelets, binding peptides derived from intracellular proteins.
Class I MHC-peptide complex is recognized by CD8+ cytotoxic T cells, which are class I MHC-restricted.
Class II MHC molecules are expressed on antigen-presenting cells, binding exogenous antigens (e.g., extracellular microbes).
Class II MHC-peptide complex is recognized by CD4+ helper T cells, which are class II MHC-restricted.

Hypersensitivity Reactions

Immunologic reactions causing disease through four main mechanisms.

Type I (Immediate) Hypersensitivity

Rapidly developing reaction occurring within minutes after antigen binds to antibody on mast cells in sensitized individuals.
Two phases:
- Immediate phase (5-30 min, subsiding in 60 min) characterized by vasodilatation and exudation due to vasoactive amine release.
- Late phase (2-4 hours, lasting for days) characterized by leukocyte influx.

Type II Hypersensitivity

Mediated by antibodies directed toward antigens on cell surfaces or extracellular matrix.
Destruction of the antigen occurs through:
- Opsonization and complement- and Fc receptor-mediated phagocytosis.
- Antibody-dependent cellular cytotoxicity (ADCC).
- Antibody-mediated cellular dysfunction.
Examples: transfusion reactions, autoimmune hemolytic anemia, drug reactions, myasthenia gravis, Grave's disease.

Type III Hypersensitivity

Antigen-antibody complexes deposit in various organs, mainly blood vessels, causing inflammation.
Examples: systemic lupus erythematosus, polyarteritis nodosa, poststreptococcal glomerulonephritis, serum sickness.

Type IV Hypersensitivity

Initiated by antigen-activated (sensitized) T lymphocytes.
Includes delayed type hypersensitivity reactions mediated by CD4+ T cells, important for defense against intracellular pathogens, transplant rejection, and tumor immunity.
Also includes direct cell cytotoxicity mediated by CD8+ T cells, mainly encountered in graft rejection.

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Description

Explore the concepts of innate and adaptive immunity in this quiz. Learn about the body's defense mechanisms, key components like T-lymphocytes, and how the immune system responds to different types of pathogens. Test your understanding of these essential concepts.