Immunology: Phagocytosis and Natural Killer Cells

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Questions and Answers

What is the primary role of antigen presenting cells (APCs)?

To secrete antibodies against antigens

To enhance phagocytic activity of macrophages

To directly destroy pathogens

To migrate to secondary lymphoid tissues and present antigens to T and B lymphocytes (correct)

Which cell marker is specifically associated with Natural Killer (NK) cells?

CD16 (correct)

CD19

CD3

CD4

How do Natural Killer (NK) cells carry out their effector mechanisms?

By enhancing the activity of macrophages

By producing antibodies that neutralize pathogens

By engulfing pathogens through phagocytosis

By releasing perforins and granzymes to induce cell death (correct)

What distinguishes NK cells from T and B cells in terms of maturation?

NK cells do not undergo thymic maturation Signup and view all the answers

What is the importance of the balance between activating and inhibitory receptors on NK cells?

To determine the activation state of the NK cells Signup and view all the answers

What type of cells are recognized and killed by NK cells during immune surveillance?

Virus-infected cells, tumor cells, and graft cells Signup and view all the answers

Which of the following statements correctly describes the process of phagocytosis by macrophages?

Macrophages degrade engulfed antigens and present their fragments to T and B cells Signup and view all the answers

What is the role of cytokines, particularly IL-2, in the function of NK cells?

They promote differentiation into lymphokine-activated killer (LAK) cells Signup and view all the answers

Which type of phagocytic cells is primarily responsible for preserving useful information from ingested particles for adaptive immunity?

Dendritic cells Signup and view all the answers

What are pathogen-associated molecular patterns (PAMPs) recognized by phagocytic cells?

Characteristic structures of microbial pathogens Signup and view all the answers

Which surface markers are expressed by Natural Killer (NK) cells?

CD16 and CD56 Signup and view all the answers

Which of the following roles is NOT associated with eosinophils?

Production of antibodies Signup and view all the answers

Which of the following correctly states the outcome of a phagocytic event in neutrophils?

Neutrophils destroy phagocytosed particles completely Signup and view all the answers

What are the main components found in the granules of mast cells?

Histamine, heparin, and leukotrienes Signup and view all the answers

What function do macrophages serve apart from phagocytosis?

Acting as antigen-presenting cells (APCs) Signup and view all the answers

Which characteristic is NOT a feature of specific immune response?

Deficiency in pathogen recognition Signup and view all the answers

Which cytokine is produced by macrophages that is important for the immune response?

IL-1 Signup and view all the answers

What is the primary function of secondary lymphoid tissues?

Concentration of foreign particles and interaction with lymphocytes Signup and view all the answers

Which type of immunity do dendritic cells and macrophages primarily bridge?

Adaptive and innate immunity Signup and view all the answers

In which tissue do B lymphocytes mature into antigen-recognizing cells?

Bone marrow Signup and view all the answers

What is a primary role of Natural Killer (NK) cells in the immune system?

Extracellular killing of infected cells Signup and view all the answers

What type of immunity is conferred by passing antibodies from a mother to her fetus?

Naturally acquired passive immunity Signup and view all the answers

Which of the following is primarily involved in the non-specific immune response?

Phagocytic cells Signup and view all the answers

Which of the following best describes a common characteristic of T cells?

They are involved in cell-mediated immunity Signup and view all the answers

What is one of the roles of IFN γ in the immune system?

Promotes the development of Tc cells. Signup and view all the answers

How does Th2 influence the immune response?

Directs immune response toward production of IgE. Signup and view all the answers

Which of the following statements is true regarding T regulatory cells?

They secrete immunosuppressive cytokines. Signup and view all the answers

What mechanism do CD8+ cytotoxic T cells use to kill target cells?

Degranulation and Fas ligand interaction. Signup and view all the answers

Which statement accurately describes the interaction between Th1 and Th2 cells?

Th1 inhibits Th2 through IFN-gamma. Signup and view all the answers

What is the primary effect of IL-10 on T cell subsets?

Down-regulates Th1 function. Signup and view all the answers

What characteristic is unique to Gamma-delta T cells?

Recognition of non-peptide antigens. Signup and view all the answers

What is the overall goal of the immune system?

To defend against invading pathogens. Signup and view all the answers

What are the primary outcomes of B cell stimulation in secondary lymphoid tissue?

Proliferation into plasma cells and memory cells Signup and view all the answers

Which cell types are produced from the maturation of T cells in the thymus?

Helper T cells and cytotoxic T cells Signup and view all the answers

Which of the following correctly describes the T cell receptor (TCR)?

It consists of two non-identical polypeptide chains linked by disulfide bonds. Signup and view all the answers

Which marker identifies regulatory T cells among T lymphocyte populations?

CD25 Signup and view all the answers

What role do CD4 T lymphocytes play in the immune response?

They assist in the activation of B cells and cytotoxic T cells. Signup and view all the answers

Which cytokine is primarily responsible for promoting T cell proliferation?

IL-2 Signup and view all the answers

Which characteristic is associated with cytotoxic T cells (CD8)?

They are responsible for killing virus-infected and cancer cells. Signup and view all the answers

What distinguishes the function of Th1 and Th2 helper T cells?

Th1 cells secrete pro-inflammatory cytokines, while Th2 cells stimulate humoral immunity. Signup and view all the answers

Study Notes

Phagocytosis

Phagocytic cells can be circulating in the blood (neutrophils and monocytes) or residing in tissues (macrophages and dendritic cells)
Phagocytic cells use pattern recognition receptors to recognize microbes which are not present on mammalian cells
Phagocytic cells recognize features of microbial pathogens called pathogen-associated molecular patterns (PAMPs)
Neutrophils destroy phagocytosed particles completely
Dendritic cells and macrophages preserve information from ingested particles and present it to adaptive immunity

Natural Killer Cells

NK cells are granular lymphocytes that can perform extracellular killing
NK cells express two surface markers: CD16 and CD56
NK cells kill virus-infected cells, tumor cells, and graft cells
NK cells perform immune surveillance and help resist bacterial, fungal, and parasitic infections
Activation of NK cells is based on a balance between activating and inhibitory receptors

Macrophages

Macrophages are released from bone marrow as immature monocytes and mature in various tissues
Macrophage functions include phagocytosing microbes, antigen presentation, and producing monokines like IL-1.
Macrophages are key cells in delayed hypersensitivity reactions, autoimmune diseases, and tumor immunity.
Macrophages help regulate immune response by releasing cytokines

Intracellular Destruction

Engulfed material is digested by lysosomal enzymes, toxic oxygen metabolites, and nitric oxide

Antigen Presenting Cells (APCs)

APCs are cells that pick up antigen and interact with T and B lymphocytes
APCs include macrophages, B-lymphocytes, and dendritic cells
Macrophages process and present antigens to T and B cells

Natural Killer Cells (NK Cells)

NK cells are derived from bone marrow
NK cells do not undergo thymic maturation
NK cells express CD56, a specific NK marker
NK cells have a receptor for the Fc portion of IgG called CD16
Cytokines, especially IL-2, promote the differentiation of NK cells into lymphokine-activated killer (LAK) cells
NK cells release cytokines like IFN γ and IL-2

Eosinophils

Play an important role in type I hypersensitivity reaction (in controlling anaphylaxis)
Have Fc & complement receptors (C3b)
Important in resistance to parasites

Mast Cells

Mast cells reside in tissues, especially under the skin and in the mucosa of respiratory and gastrointestinal tracts.
Mast cells contain histamine, heparin, serotonin, leukotrienes, and prostaglandins
Mast cells initiate anaphylaxis on stimulation by antigen and IgE or when activated by C3a, C5a

Specific Immune Response

Specific immune response has four essential characteristics: provides additional protection, specificity, distinguishes self from non-self, and memory

Acquired Immunity

Naturally acquired: passive antibodies from mother to fetus (placenta-milk) and active recovery from infections
Artificially acquired: active vaccines and passive immunoglobulins

Tissues and Cells of Specific Immune Response

Central (primary) lymphoid tissues: Thymus (T cell maturation) and Bone marrow (B cell maturation)
Peripheral (secondary) lymphoid tissues: Spleen, lymph nodes, mucosa- associated lymphoid tissue (MALT)

Cells Involved in Immune Response

B cells (specific immune response)
T cells (specific immune response)
Natural killer cells (non-specific immune response)
Phagocytic cells (non-specific immune response): monocytes (macrophages) and neutrophils
Other cells: eosinophils and mast cells

B Lymphocytes

Constitute 15–20% of circulating lymphocytes
Short lifespan (days or weeks)
Mature in the bone marrow from stem cells
B cell development originates from stem cells in the bone marrow
B cells proliferate and differentiate into plasma cells (secrete antibodies) and memory cells (rapid plasma cell proliferation on secondary immune response)

B Cell Stimulation

B cells are stimulated by antigens, which bind to antigen receptors on the B cell surface
Stimulation activates B cell proliferation and differentiation

T Lymphocytes

Constitute 65-80% of circulating lymphocytes
Mature in the thymus from stem cells
T cells acquire CD2, CD4, and CD8 in the thymus cortex
T cells acquire CD3 in the thymus medulla
T cells differentiate into two main populations: CD2, CD3, CD4 (helper or delayed sensitivity T-lymphocyte (CD4) and CD2, CD3, CD8 (cytotoxic T-lymphocyte (CD8)

T Lymphocyte Subpopulations

CD2, CD3, CD4: Helper
CD2, CD3, CD8: Cytotoxic
CD2, CD3, CD4, CD 25: Regulatory

T Cell Receptor

T cells have an antigen receptor called the T cell receptor (TCR)
TCR consists of two non-identical polypeptide chains (alpha and beta) linked by disulfide bonds

Other T Cell Markers

Receptors for the Fc portion of Ig
CD antigens (cluster of differentiation)
CD2: sheep red blood cell receptor (SRBC-R)
CD3: associated with TCR; important for signal transduction during antigen presentation
CD4, CD8: receptors that bind MHC molecules during antigen presentation

CD4+ T Lymphocytes

65% of T lymphocytes
Called T helper (Th) cells
Help B cells and macrophages in the induction of humoral immune response
Help Tc cells
Two types: Th1 and Th2

Th1 Cells

Secrete cytokines including IL-2, IFN γ, and TNF β
IL-2 promotes T cell proliferation and activation of B cells and NK cells
IFN γ has diverse functions: promotes Tc cell development, induces MHC expression, antiviral effect, activates macrophages and NK cells, increases Fc receptor expression, and regulates cell-mediated immunity

Th2 Cells

Direct immune response toward the production of IgE
Secrete cytokines including IL4, IL5, and IL10
IL4 enhances class switching to IgE
IL10 downregulates Th1 function
IL5 mediates eosinophil and mast cell proliferation

Treg Cells

Inhibit T cell proliferation and cytokine production
Originally called suppressor T cells
Secrete immunosuppressive cytokines like transforming growth factor-β (TGFβ) and IL-10
Suppress Ig production by B cells
Prevent atopy by suppressing IgE secretion
Prevent autoimmunity by inhibiting self-reacting lymphocyte clones

CD8+ T cells

CD8+ cytotoxic T cells (Tc cells)
Constitute 35% of peripheral T lymphocytes
Induced by, and are active against, tumors, viruses, and allogenic grafts
Cause lysis of antigen-bearing target cells
Mechanisms of killing by CD8+ CTLs: degranulation (granzymes and perforins) and Fas ligand-Fas pathway

Gamma-delta T Cells

These cells are a subset of T cells that express a TCR with gamma and delta chains instead of alpha and beta chains
They are thought to be involved in innate immunity and play a role in recognizing stress molecules and mediating inflammatory responses.

Summary

The immune system is a complex system that protects the body from invading pathogens and foreign agents.
The immune system involves both innate and adaptive mechanisms, which work together and can be stimulated to release various mediators that defend against foreign invaders.

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Description

This quiz covers key concepts about phagocytosis and the role of natural killer (NK) cells in the immune system. Learn about the different types of phagocytic cells, their recognition mechanisms, and how NK cells contribute to immune defense against infections and tumors. Test your knowledge on their functions and interactions within the immune response.