Microbiology Lecture 14: Specific Defenses

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Questions and Answers

What type of defense is characterized by the body’s ability to recognize and defend against distinct invaders?

Innate defenses

Specific defenses (correct)

Nonspecific defenses

Physical barriers

Which of the following is NOT considered a part of the first line of defense in immune response?

Phagocytosis (correct)

Skin

Microbial antagonism

Mucous membranes

What is a main characteristic of the specific immune response?

It is acquired over time. (correct)

It lacks memory functions.

It does not distinguish between types of pathogens.

It acts immediately upon pathogen exposure.

What role do lymphocytes play in the immune response?

They are involved in the specific immune response. Signup and view all the answers

How does the immune system demonstrate memory functions?

By recognizing and responding faster to familiar pathogens. Signup and view all the answers

What defines an epitope in the context of antigens?

A defined region of a molecule with antigenic properties Signup and view all the answers

What role does the lymphatic system play in the immune response?

It screens tissues for foreign antigens and helps maintain fluid balance. Signup and view all the answers

Which of the following is NOT a method by which antigens can enter the body?

Through direct sunlight exposure Signup and view all the answers

Which components are included in the lymphatic system?

Lymphoid cells, lymphatic vessels, and various organs Signup and view all the answers

Which of the following statements about antigens is true?

Antigens can be proteins found in bacteria, fungi, and food particles. Signup and view all the answers

What is lymph primarily composed of?

Fluid leaked from blood vessels Signup and view all the answers

Where do lymphocytes primarily mature?

Thymus and red bone marrow Signup and view all the answers

What is the function of lymph nodes?

House leukocytes that attack foreign antigens Signup and view all the answers

Which organ is involved in filtering bacteria and viruses from the blood?

Spleen Signup and view all the answers

What happens during clonal selection of lymphocytes?

They divide upon activation by an antigen Signup and view all the answers

Which of the following structures helps trap foreign particles and microbes?

Tonsils and MALT Signup and view all the answers

What type of cell is a lymphocyte?

White blood cell Signup and view all the answers

What is the primary role of lymphatic vessels in the body?

To collect lymph and return it to circulation Signup and view all the answers

What is the role of T helper cells (CD4) in the immune response?

Recognize MHC/Ag complex and direct the immune response Signup and view all the answers

Which type of cell directly eliminates cancer and virus-infected cells?

T cytotoxic cells Signup and view all the answers

Where are T cells produced and matured?

Red bone marrow and thymus Signup and view all the answers

What triggers the cell-mediated immune response?

Display of pathogen-derived antigens on host cell membranes Signup and view all the answers

What mechanism do T cells employ to eliminate antigen-presenting cells?

Release of perforin and granzyme Signup and view all the answers

What is the significance of MHC recognition for T cells?

It allows the immune system to remove foreign cells. Signup and view all the answers

Which component is NOT involved in the cell-mediated immune response?

B lymphocytes Signup and view all the answers

What is the result of improper regulation of T cell responses?

Autoimmune disorders Signup and view all the answers

What is the primary role of plasma B cells in the humoral immune response?

To secrete large quantities of antibodies specific to an antigen Signup and view all the answers

Which of the following best describes the function of memory B cells?

They display antibodies on their membranes without secreting them. Signup and view all the answers

What is the significance of clonal selection in the humoral immune response?

It allows for the selection of B cells that will become plasma cells. Signup and view all the answers

What is the primary purpose of lymphocyte editing via clonal deletion?

To eliminate self-reactive lymphocytes Signup and view all the answers

Antigen-presenting cells (APCs) are crucial for B cell activation because they do what?

Display antigens on their surface to signal T-helper cells. Signup and view all the answers

Which cells are primarily responsible for synthesizing and secreting antibodies?

Plasma cells Signup and view all the answers

What triggers the activation of B cells during the humoral immune response?

Signals from T-helper cells through interleukins. Signup and view all the answers

What is a key characteristic of the antibodies' structure?

They are composed of light and heavy chains Signup and view all the answers

What is the main difference between plasma B cells and memory B cells?

Plasma B cells produce antibodies immediately, while memory B cells are for future responses. Signup and view all the answers

Which process involves the immune system sourcing antigen-specific B cells for a stronger response?

Clonal selection Signup and view all the answers

Which class of antibody is primarily involved in mucosal immunity?

IgA Signup and view all the answers

What process occurs during the maturation of B cells that contributes to heterogeneity?

Randomization of variable region receptors Signup and view all the answers

What role do cytokines play in B cell activation?

They signal B cells to proliferate and differentiate. Signup and view all the answers

Which interaction is primarily responsible for the binding of an antibody to its antigen?

Hydrogen bonds and other attractions Signup and view all the answers

How do T cells recognize self-antigens during clonal deletion?

By recognizing MHC class I molecules Signup and view all the answers

What type of immune response are antibodies primarily associated with?

Humoral immune response Signup and view all the answers

Which of the following is NOT a class of antibodies?

IgC Signup and view all the answers

What triggers the differentiation of activated B cells into memory cells?

Exposure to antigens after initial activation Signup and view all the answers

Study Notes

Microbiology - Lecture 14: Specific Defense Mechanisms

Defense Mechanisms (Overview):
Innate defenses provide natural resistance to pathogens.
Nonspecific defenses include first line (skin, mucous membranes, microbial antagonism) and second line (phagocytosis, inflammation, fever, signaling molecules).
Specific defenses are the third line, involving lymphocytes and antibodies.

Third Line of Defense (Specific Immunity)

Specific Immunity:
The body's ability to recognize and defend against distinct invaders.
"Smart" system with memory for rapid response to subsequent encounters.
Acquired over time through exposure.
Includes antigens, the lymphatic system, B cells, antibodies, humoral immunity, and cell-mediated immunity.

Antigens

Antigens:
Any molecule or molecular fragment triggering a specific immune response.
Includes components of bacterial cell walls, capsules, pili, flagella, viral proteins, fungal components, and protozoan proteins.
Epitope is the region of a molecule with antigenic properties. A single molecule may have multiple epitopes.
Antigens can enter the body through various pathways such as breaks in the skin, mucous membranes, injections, or transplants.

Lymphatic System

Lymphatic System:
A network of organs, vessels, and cells that screen the body for foreign antigens.
Lymphatic vessels collect lymph from tissues and return it to the circulatory system.
Lymph nodes, spleen, and tonsils are key components.
Lymph is similar to blood plasma, formed from leaked blood fluid.

Lymphocytes (Overview)

Lymphocytes:
Arise and mature in red bone marrow (B cells) or thymus (T cells).
Primarily found in the spleen and lymph nodes, with a smaller percentage circulating in the blood.
Activated by a single matching antigen, leading to cell division and the formation of memory cells.

Lymphocyte Editing by Clonal Deletion

Clonal Deletion:
A critical process to eliminate lymphocytes that respond to self-molecules (autoantigens).
Ensures the immune system does not attack the body's own cells.

Characteristics of B Cells

B Cells:
Originate from stem cells in bone marrow.
Clonal deletion inactivates B cells that respond to self antigens.
Diverse range of B cells (heterogeneity).
Each B cell has two matching receptors.
Antigen binding is highly specific.
Activated B cells develop into plasma cells (antibody secretion) or memory cells (rapid response to subsequent encounters).

Antibodies (Immunoglobulins)

Antibodies:
Soluble proteins composed of polypeptide chains (held by covalent bonds).
Circulate in blood and lymph, binding to antigens for neutralization, opsonization, or complement activation.
Secreted by plasma cells (activated B cells).
Part of the humoral immune response.

Structure of Antibodies

Antibody Structure:
Four polypeptides (2 heavy, 2 light chains), connected by covalent bonds.
Y-shaped molecule with two antigen-binding sites.
Constant region (Fc region) determines class.
Variable region (arms) binds to specific antigens.

Classes of Antibodies

Antibody Classes:
Different classes of antibodies have various roles in the immune response (IgA, IgD, IgE, IgG, IgM).

Antibody Function

Antibody Function:
Form strong, non-covalent interactions with antigens.
Interactions involve complement activation, inflammation, agglutination, neutralization, and opsonization.

Humoral Immune Response

Humoral Immune Response:
Antibody-mediated response against exogenous pathogens.
Involves B cell activation, clonal selection, plasma cell differentiation, and antibody secretion.
Requires the help of T helper cells.

Cell-Mediated Immunity

Cell-Mediated Immunity:
Involves T cells that directly attack cells with abnormal antigens (virus-infected cells, cancer cells).

Type T Lymphocytes (T Cells)

T Cells:
Produced in bone marrow, mature in thymus.
Crucial for recognizing MHC (major histocompatibility complex) / antigen complexes.
Two main types: T helper cells (CD4) and cytotoxic T cells (CD8).

Cell-Mediated Immune Response

Cell-Mediated Immune Response:
T cells act directly against various antigens (intracellular pathogens and abnormal body cells).
Triggered when host cells display antigens on their membrane.
Leads to memory T cell formation for subsequent responses.

Regulation of Cell-Mediated Response

Regulation of Cell-Mediated Response:
Carefully regulated to prevent T cells from responding to autoantigens (self-antigens).
T cells need activation signals provided by antigen-presenting cells.
Apoptosis (programmed cell death) is crucial for regulating cell-mediated responses.

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Description

Explore the mechanisms of specific defenses against pathogens in microbiology. This quiz covers innate and specific immunity, detailing the roles of lymphocytes and antibodies, and the function of antigens. Test your knowledge of how the body recognizes and responds to distinct invaders.