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Adaptive immunity

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Page 1: Adaptive immunity

April 11, 20231

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Department: MicrobiologySemester: 2nd

Class no: 02

Tajuddin

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Topic of presentation

Adaptive Immunity

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Body defense mechanisms & its characteristics Adaptive immunity & Its responses to antigens Cells of Adaptive Immune Response Organs of Immune Responses Types of Adaptive immunity Role of Antigens receptors & Cytokines in

Immune Response T-Dependent Vs T-Independent Antigens

Over view of Presentation

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Immune system depend us from

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Defense Mechanisms

1.External defense2.Internal Defense3.Immune Defense

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Characteristics of Adaptive Immunity

• Recognition of self versus non-self

• Response is specific• Retains a “memory”

allowing an accelerated second response

• Can respond to many different materials

• Involves lymphocytes and antibodies

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Acquired immunity (Adaptive or Specific)

Humoral Immunity Cell mediated Immunity

Acquired (Adaptive) Immunity

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The adaptive or specific immune response involves two main lines of defence: humoral immunity and cell mediated immunity. Humoral immunity involves B lymphocytes (B

cells) Cell-mediated immunity involves T lymphocytes

(T cells)

Both B cells and T cells are derived from stem cells in the bone marrow, however they mature in different parts of the body. B cells mature in the bone marrow then travel to

lymphatic tissues, especially the spleen and lymph nodes

T cells mature in the thymus

Humoral and cell-mediated immunity

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Lymphocyte Formation

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Immune System Response to Antigens

Humoral Immunity• Involves antibodies (secreted

from B cells) dissolved in the blood plasma.

• Demonstrated as an immune response using only the blood serum(Plasma without clotting protiens).

• Defense against bacteria, bacterial toxins, & viruses binding to its Epitopes.

• Epitope(Antigenic determinent)

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Cell-Mediated Immunity• Involves the activities of specific

white blood cells (T cells).• Defense against cancer cells, virus-

infected cells, fungi, animal parasites, & foreign cells from transplants.

Immune System Response to Antigens (cont.)

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Cells involved in specific immune mechanisms are:

I) Hematopoitic leucocytes(derived from mesoderm)

1- Lymphoid * T-lymphocytes: - Antigen specific cells carrying CD3 complex,

CD4, CD8

- Dominant blood lymphocytes (70%) - Produce cytokines - Activation of other cells (Th CD4) - Suppressors for others (Ts CD8)

Cells Of Immune Response

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* B-lymphocytes: - Antigen specific cells with surface

receptor - Less common lymphocytes (20%) - Responsible for antibody production

* NK, K cells: - Not antigen specific - Carry Fc receptors , NK-target cell

receptor

Cells Of Immune Response (cont.)

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2- Monocytic myeloid

a- Monocyte-tissue macrophages: . Non specific . Carry Fc receptors . Phagocytic . Antigen processing and presenting cells . Produce cytokines

b- Neutrophils: . Non specific . Carrying Fc, complement molecules

Cells of Immune Response (cont.)

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Cells of Immune Response (cont.)

c- Eosinophil: . Non specific . Carrying Fc receptor . Produce allergic mediators

d- Basophils and Mast cells: . Non specific . Carrying Fc receptors . Produce allergic mediators

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ІІ-Non hematopoietic cells: - Dendritic cells - Astrocytes and - Endothelial cells

Function : antigen presentation

Cells of Immune Response (cont.)

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Cells of the immune system Bone graft

Multipotential

stem cell

Hematopoieticstem cell

Platelets

Macrophage

ErythrocytesEosinophil

Neutrophil

Megakaryocyte

Mast cell

Basophil

T lymphocyte

Natural killer cell

Dendritic cell

B lymphocyte

Lymphoid progenitor cell

Myeloid progenit

or cell

Monocyte

Marrow

Bone

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Tonsils andadenoids

Lymphnodes

Appendix

Lymphaticvessels

Lymph nodes

Thymus

Peyer’spatches

Spleen

Lymphaticvessels

Lymph nodes

Organs of the Immune Response• The organs of our immune

system are positioned throughout our body.

• They are called lymphoid organs because they are home to lymphocytes--the white blood cells that are key operatives of the immune system. Within these organs, the lymphocytes grow, develop, and are deployed.

• Key organs include the bone marrow, the thymus and the spleen.

• In addition to these organs, clumps of lymphoid tissue are found in many parts of the body, especially in the linings of the digestive tract and the airways and lungs--gateways to the body. These tissues include the tonsils, adenoids and appendix.

Bonemarrow

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The production of antibodies against a specific disease by the immune system.

Naturally acquired through disease Artificially acquired through vaccination

Vaccines include inactivated toxins, killed microbes, parts of microbes, and viable but weakened microbes.

Active immunity is usually permanent

Active Immunity

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A vaccinated person has a secondary response based on memory cells when encountering the specific pathogen. Routine immunization against infectious

diseases such as measles and whooping cough, and has led to the eradication of smallpox, a viral disease.

Unfortunately, not all infectious agents are easily managed by vaccination.

HIV vaccine in the works

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Active Immunity (cont.)

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Passive Immunity- Protection against disease through antibodies produced by another human being or animal.

Effective, but temporary Maternal antibodies (IgG) Colostrum (IgA)

Passive Immunity

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Passive immunity can be transferred artificially by injecting antibodies from an animal that is already immune to a disease into another animal. Rabies treatment: injection with

antibodies against rabies virus that are both passive immunizations (the immediate fight) and active immunizations (longer term defense).

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Passive Immunity (Cont.)

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B Cells

• Mature in bone marrow• Involved in humoral immunity• Once activated by antigen,

proliferate into two clones of cells: plasma cells that secrete antibodies and memory cells that may be converted into plasma cells at a later time April 11, 202325

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B Cells

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Release of Antibodies from Plasma cell

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Antibodies constitute a group of globular proteins called immunoglobins (Igs). A typical antibody molecule has two

identical antigen-binding sites specific for the epitope that provokes its production.

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Antibodies

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Antibody Molecule

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Immunoglobin ClassesIgM• 1st response to antigen• Can’t cross placenta• Involved in agglutination and complement activation

IgG• Most common form• Crosses blood vessels• Crosses placenta (passive

immunity to fetus)• Involved in agglutination

and complement activation

IgA• Secreted from mucus

membranes• Prevents attachment of bacteria

to epithelial surface• In colostrum• Important in mucosal immunity

IgD• B cell activation• Can’t cross placenta• Important in development of the immune response

IgE• Histamine

reactions and allergies

• Attaches to mast cells

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Mechanisms on Antibody Action

• Precipitation of soluble antigens• Agglutination of foreign cells• Neutralization• Enhanced phagocytosis• Complement activation leading to cell lysis• Stimulates inflammation

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The binding of antibodies to antigens to form antigen-antibody complexes is the basis of several antigen disposal mechanisms.

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The classical complimentary pathway, resulting in lysis of a

target cell

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T Cells• Mature in thymus• Involved in cell-mediated

immunity• Activated when another cell

presents antigen to them• Several types of T cells:

cytotoxic T cells, helper T cells, suppressor T cells, and memory T cells April 11, 202334

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• There are two main types of T cells, and each responds to one class of MHC molecule.– Cytotoxic T cells (TC) have antigen

receptors that bind to protein fragments displayed by the body’s class I MHC molecules.

– Helper T cells (TH) have receptors that bind to peptides displayed by the body’s class II MHC molecules.

T Cells

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The central role of helper T cells

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Role of antigen receptors in the immune response

• Both B cells and T cells carry customized receptor molecules that allow them to recognize and respond to their specific targets.

• The B cell’s antigen-specific receptor that sits on its outer surface is also a sample of the antibody it is prepared to manufacture; this antibody-receptor recognizes antigen in its natural state.

• The T cell’s receptor systems are more complex. T cells can recognize an antigen only after the antigen is processed and presented in combination with a special type of major histocompatibility complex (MHC) marker.

• Killer T cells only recognize antigens in the grasp of Class I MHC markers, while helper T cells only recognize antigens in the grasp of Class II MHC markers. This complicated arrangement assures that T cells act only on precise targets and at close range.

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Antigen receptors Killer cell

Infected cellAntigen-presenting cell

Antigen-presenting cell

CD8 protein

Cell membrane

MHC Class I

MHC Class I

Antigenic peptide

T cell receptorCD4

protein

Cell membrane

MHC Class II

Antigenic peptide

T cell receptor

Cell membrane

Antigen

Antigen-specific receptor

B cell

Killer cell

Infected cellAntigen-presenting cell Antigen-presenting cell

CD8 protein

Cell membrane MHC

Class IMHC Class I

Antigenic peptide

T cell receptor

CD4 protein

Cell membrane MHC

Class II

Antigenic peptide

T cell receptor

Cell membrane

Antigen

Antigen-specific receptor

Helper T cellB cell

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Role of cytokines in immune response• Cytokines are diverse and potent chemical messengers

secreted by the cells of immune system. They are the chief communication signals of our T cells. Cytokines include interleukins, growth factors, and interferon.

• Lymphocytes, including both T cells and B cells, secrete cytokines called lymphokines, while the cytokines of monocytes and macrophages are dubbed monokines. Many of these cytokines are also known as interleukins because they serve as a messenger between white cells, or leukocytes.

• Interferon are naturally occurring cytokines that may boost the immune system’s ability to recognize cancer as a foreign invader.

• Binding to specific receptors on target cells, cytokines recruit many other cells and substances to the field of action. Cytokines encourage cell growth, promote cell activation, direct cellular traffic, and destroy target cells--including cancer cells.

• When cytokines attract specific cell types to an area, they are called chemokines. These are released at the site of injury or infection and call other immune cells to the region to help repair damage and defend against infection.

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T-independent antigensT cells activated by binding to certain antigens

No memory cells generatedWeaker response than t-dependent

T-dependent antigensMost antigens require co-stimulation to evoke a B-cell response

Antibody production stimulated with help from TH

Most antigens are t-dependent

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Overview of Immune System Responses

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Any Question???

Thanks 4 your Attention

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