ROBERT W. BAUMAN Chapter 16

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

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ROBERT W. BAUMAN

MICROBIOLOGY

Chapter 16

Specific Defense: The Immune Response


• Is called specific immunity

• The body’s ability to recognize and defend itself against distinct invaders and their products

• Is a “smart” system whose “memory’ allows it to respond rapidly to a second encounter with a pathogen

• Specific Immunity

• Humoral immunity - Involves Ab produced by B cells

• Cell-mediated immunity - Involves T cells

Third Line of Defense


• Acquired over time

• Immunology = study of the cells and chemicals involved in specific immunity

• Antigens trigger specific immune responses

• Various cells, tissues, and organs are part of specific immunity

• Includes B and T lymphocytes

Elements of Specific Immunity


Terminology

• Innate (nonspecific) - Defenses against any pathogen

• Immunity - Specific antibody and lymphocyte response to an antigen

• Antigen (Ag) - A substances that causes the body to produce specific antibodies or sensitized T cells

• Antibody (Ab) - Proteins made in response to an antigen


• Screens the tissues of the body for foreign antigens

• Composed of lymphatic vessels and lymphatic cells

• Lymphatic Vessels

• Form a one-way system that conducts lymph from local tissues and returns it to the circulatory system

• Lymph is a liquid

• similar composition to blood plasma

• arises from fluid leaked from blood vessels into surrounding tissues

Lymphatic System

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 16.2


• Develop from stem cells in the red bone marrow

• Includes lymphocytes, the smallest of the leukocytes

Lymphoid Cells

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 16.3b


• Houses leukocytes that recognize and attack foreign antigens present in the lymph

• Concentrated in the cervical (neck), inguinal (groin), axillary (armpit), and abdominal regions

• Receives lymph from afferent lymphatic vessels and drains lymph into efferent lymphatic vessels

Lymph Nodes


• Spleen

• Similar in structure and function to the lymph nodes

• Filters bacteria, viruses, toxins, and other foreign matter from the blood

• Tonsils and mucosa-associated lymphoid tissue (MALT)

• Physically trap foreign particles and microbes

• MALT includes the appendix, lymphoid tissue of the respiratory tract, and Peyer’s patches in the wall of the small intestine

Other Lymphoid Tissues and Organs


• Arise and mature in the red bone marrow

• Found primarily in the spleen, lymph nodes, red bone marrow, and Peyer’s patches

• Small percentage of B cells circulate in the blood

• Major function is the secretion of antibodies

B Lymphocytes


• Also called immunoglobulins (Ig)

• Soluble, proteinaceous molecules that bind antigen

• Secreted by plasma cells, which are B cells actively fighting exogenous antigen

• Part of the humoral immune response

• (bodily fluids such as lymph and blood were once called humors)

Antibodies


Terminology

• Serology - Study of reactions between antibodies and antigens

• Antiserum - Generic term for serum (because it contains Ab)

• Globulins - Serum proteins

• Gamma () globulin - Serum fraction containing Ab


Serum Proteins

Figure 17.2



• Antigen-binding sites are complementary to antigenic determinants (epitopes)

• Due to the close match can form strong, noncovalent interactions

• Hydrogen bonds and other attractions may also be involved

Antibody Function


• Molecules that trigger a specific immune response

• components of bacterial cell walls, capsules, pili, and flagella,

• proteins of viruses, fungi, and protozoa

• Food and dust can also contain antigenic particles

• Enter the body by various methods

• Through breaks in the skin and mucous membranes

• Direct injection, as with a bite or needle

• Through organ transplants and skin grafts

Antigens



Antigenic Determinants

• Antibodies recognize and react with antigenic determinants or epitopes.

Figure 17.3


Haptens

Figure 17.4


Antibody Structure

Figure 17.5a-c


• Monomer

• 80% of serum antibodies

• Fix complement

• In blood, lymph, intestine

• Cross placenta

• Enhance phagocytosis; neutralize toxins & viruses; protects fetus & newborn

• Half-life = 23 days

IgG antibodies


• Pentamer

• 5-10% of serum antibodies

• Fix complement

• In blood, lymph, on B cells

• Agglutinates microbes; first Ab produced in response to infection


IgM antibodies


• Dimer

• 10-15% of serum antibodies

• In secretions

• Mucosal protection


IgA antibodies


• Monomer

• 0.2% of serum antibodies

• In blood, lymph, on B cells

• On B cells, initiate immune response


IgD antibodies


• Monomer

• 0.002% of serum antibodies

• On mast cells and basophils, in blood

• Allergic reactions; lysis of parasitic worms


IgE antibodies



Characteristics of the Five Classes of Immunoglobulins

Table 16.1


• Bone marrow gives rise to B cells.

• Mature B cells migrate to lymphoid organs.

• A mature B cells recognizes epitopes.

Clonal Selection


Clonal Selection

Figure 17.8


• = antibody that remains associated with the cytoplasmic membrane

• Each B lymphocyte has multiple copies of a single type of BCR

• Antigen binding site is identical to that of the secreted antibody for that particular cell

• Each BCR is complementary to only one antigenic determinant

• The BCRs on all of an individual’s B cells are capable of recognizing millions of different antigenic determinants

B Cell Receptor (BCR)


Self-tolerance

• Body doesn't make Ab against self

• Clonal deletion

• The process of destroying B and T cells that react to self antigens


The Results of Ag-Ab Binding

Figure 17.9



• Function in several ways

• Activation of complement

• Stimulation of inflammation

• Agglutination

• Neutralization

• Opsonization

Antibody Function


Antibody titer:

• Is the amount of Ab in serum

Figure 17.10


• Specialized lymphocytes, mostly T cells, respond to intracellular Ags

• After differentiating in the thymus, T cells migrate to lymphoid tissue

• T cells differentiate into effector T cells when stimulated by an Ag

• Some effector T cells become memory cells

Cell-Mediated Immunity


• Produced in the red bone marrow and mature in the thymus

• Circulate in the lymph and blood and migrate to the lymph nodes, spleen, and Peyer’s patches

• Part of the cell-mediated immune response because they act directly against various antigens

• Endogenous invaders

• Many of the body’s cells that harbor intracellular pathogens

• Abnormal body cells such as cancer cells that produce abnormal cell surface proteins

T Lymphocytes




• Cytotoxic T Cells (CD8, TC)

• Destroy target cells with perforin

• Virus or intracellular pathogen infected cells, cancer cells

• Helper T Cells (CD4, TH) – regulate activity of B & T cells; secrete cytokines

• TH1 Activate cells related to cell-mediated immunity, cytotoxic T cells

• TH2 Activate B cells to produce eosinophils, IgM, and IgE

T Cells


• Delayed Hypersensitivity T Cells (TD)

• Associated with allergic reaction, transplant rejection, and tuberculin skin test

• Suppressor T cells (TS)

• Turn off immune response when Ag no longer present

T Cells


• 2 types

• Type 1 helper T cell (TH1)

• Assist cytotoxic T cells

• Express CD26 and a cytokine receptor named CCR5

• Type 2 helper T cell (TH2)

• Assist B cells

• Have cytokine receptors CCR3 and CCR4

Helper T Cells (TH Cells)


Helper T Cells

Figure 17.13


Cell-mediated Cytotoxicity

Figure 17.14


Nonspecific Cells

• Activated macrophages: Macrophages stimulated by ingesting Ag or by cytokines

• Natural killer cells: Lymphocytes that destroy virus-infected cells, tumor

Figure 17.15


• Major histocompatibility antigens are glycoproteins found in the membranes of most cells of vertebrate animals

• Function to hold and position antigenic determinants for presentation to T cells

• First identified in graft patients

• Important in determining the compatibility of tissues in successful grafting

Major Histocompatibility Complex (MHC)



• T-independent antigen

• Large antigen molecules with readily accessible, repeating antigenic determinants

• B cells can bind these directly without being processed

• Stimulates B cells to differentiate into a plasma cell and produce antibodies

Antigen Processing


T-independent Antigens

Figure 17.17

B cell


• T-dependent antigens

• Smaller antigens with less accessible antigenic determinants

• B cells require involvement from helper T cells to target these antigens

• Helper T cells are assisted by leukocytes that process the antigen to make the antigenic determinants more accessible

• Processing is different based on whether the antigen is exogenous or endogenous

Antigen Processing


T-dependent Antigens

Figure 17.16


• Body mounts humoral immune responses against exogenous pathogens

• Components of a humoral immune response

• B cell activation and clonal selection

• Memory B cells and the establishment of immunological memory

Review of Humoral Immune Response



• Responds to intracellular pathogens and abnormal body cells

• The most common intracellular pathogens are viruses but the response is also effective against intracellular bacteria

• Triggered when antigenic determinants of the pathogen are displayed on the host cell’s surface

Review of Cell-Mediated Immune Response




Humoral Immunity & Cell-Mediated Immunity


Antibody-Dependent Cell-Mediated Cytotoxicity

Figure 17.18

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ROBERT W. BAUMAN Chapter 16

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