Immunity

Part IIBiology 2122Chapter 21

Adaptive or Specific Immune Response

Introduction▫Specific against a single pathogen▫Systemic ▫Memory capabilities

1. Humoral Immunity▫B-Cell Lymphocytes produce antibodies▫Antibodies bind to a specific antigen and immobilize them

2. Cell-mediated Immunity▫ Lymphocytes defend the body▫Centers on Cellular targets

Antigens ‘Antigens’ - large complex natural and synthetic molecules

• foreign to the body.

They provoke an immune response.

Antibodies or lymphocytes• ‘specific’ for an antigen bind to

antigens at the part called ‘antigenic determinant’ binding sites.

One antigen may contain several binding sites

• several antibodies may attach to them and provoke the immune response.

Immunogenicity and Reactivity

Complete Antigens have both of these properties.

Immunogenicity is the ability of a antigen to cause the production of lymphocytes and antibodies

▫They are reactive ▫Have the ability to react with the activated lymphocytes and

antibodies released by immunogenic reactions.

Complete Antigens▫Microbes, nucleic acids, lipids, poylsaccharides, proteins

(strongest), pollen grains.

Antigens

Incomplete antigens (haptens) •Small peptides, hormones, etc.

▫They are not immunogenic▫but if they bond with the body’s proteins, can

cause an attack by the immune response that is harmful

▫Examples are poison ivy, animal dander, cosmetics, products used in the house hold

▫Antigen Animations

Antibody Structure ‘Immunoglobulins’

•Composed of heavy chains and light chains.

The variable region changes depending on the antigen it will react with. •These combine with the antigen-binding sites

•C or constant region - dictates the cells and chemicals it can bind to.

Immunoglobulin Classes 1. IgM – on B-surface cell (antigen

receptor)2. IgA – plasma, in saliva, sweat, etc. 3. IgD – B-cell; antigen receptor 4. IgG – most abundant; protects against

bacteria, viruses, toxins5. IgE – plasma cells in skin, GI mucosae,

respiratory tract

Monoclonal Antibodies

• Antigen-Antibody Testing Complexes

• Pregnancy Testing

MHC Proteins – Recognizing ‘Self’• Your cells – surface proteins– MHC proteins (glycoproteins) – ‘Self-Antigens’

• Classes of MHC Proteins– 1. MHC I – all body cells– 2. MHC II – only on immune response

cells

• Role in adaptive defense system

Cells of the Adaptive Immune System

Immature lymphocytes •produced in the bone marrow - will mature into a B or T lymphocytes•Each become immunocompetent in different locations▫ T-lymphocytes in the thymus▫ B-lymphocytes in the bone marrow

Positive selections •refers to the process of selecting T cells whose receptors that can recognize self-MHC molecules.

T-cells then proceed to negative selection in the thymus ▫If a T-cell binds too tightly to a self-MHC are eliminated▫The cells that survive has developed self-tolerance (unresponsiveness to self-antigens)

Lymphocyte mobilization

T CELL SELECTION – Positive and Negative Selection

Cells of the Adaptive Immune System

When these cells become immunocompetent •display receptors on their surface ▫It is committed to one and only one antigen! ▫This process occurs prior to encountering an

antigen. ▫These receptors are determined by our genes.

After they become immunocompetent •migrate to Lymph nodes, spleen, lymph organs

The final maturation of the T or B cells •when they encounter and lock onto an antigen.

What are Antigen-Presenting Cells?

Dendritic cells in CT, Langerhans’ cells of the epidermis, macrophages and activated B-cells.

Ingest antigens - present parts of the antigen on their surface.

Encountered by T-cells - antigen presentation▫ T cells circulate throughout the body. ▫ Role of T-Cells

APCs are found in great concentrations in: ▫Lymph node Paracortical area ▫B-cells - germinal centers of the spleen. ▫Macrophages in medullary sinus of spleen (fixed)

•APC Animation

Humoral Immune Response

Naïve B-lymphocytes (immunocompetent) •bind to antigens and then undergo a process called clonal selection.

B-cell clone division •produces different types of B-cells– B-cells attach to antigens in the ‘extracellular

environment’

Most become plasma cells which secrete antibodies.

Others differentiate into memory cells •mount an immediate response on future encounters with the antigen.

Humoral Response- Clonal Selection of B-Cells

Humoral Response

• Humoral Animationhttp://bcs.whfreeman.com/thelifewire/content/chp18/1802004.html

Memory Primary immune Response ▫first exposure - 3-6 day lag ▫B cells - go through clonal selection ▫differentiate into plasma cells ▫antibody levels peak in 10 days

Secondary Immune Response ▫Second exposure; faster and more effective ▫Plasma cells produced hours after antigen exposure ▫2-3 days antibody concentration increases and remains

high for several weeks ▫antibodies bond more efficiently with antigens ▫may remain for life

Humoral Responses

Active and Passive Humoral Immunity

1. Active Humoral Immunity▫B cells encounter antigens - produce antibodies

(a) naturally acquired(b) artificially acquired Vaccine Animation

2. Passive Humoral Immunity▫Donor’s antibodies injected into the bloodstream of another person ▫Crossing of mother’s antibodies to placenta (naturally acquired)–Short-lived; no memory is established

▫Artificially acquired by injection of immune serum

Action of Antibodies

1. Antibodies work with the complement protein system.

Cell-Mediated Immune Response

Antibodies provide very little protection against antigens that invade body cells. – Ineffective (viruses, other intercellular

pathogens)

Cell-Mediated Immune Response– T-Cells (TH – CD4); (TC – CD8); (memory,

regulatory T-Cells)– T-Cells only recognize “processed” or presented

fragments of antigens.– Cell-Mediated Immune Response Animation

T-Cell Development 1. CD4 and CD8 T-Cells

mature in the Thymus Gland.

2. Activated by ‘APCs’. 3. Class-I MHC

proteins: displayed by most all body cells; recognized by CD8 cells. Becomes activated into TC cells and Suppressor T- Cells

4. This process is endogenous (endogenous antigen)

1. Class II MHC: Immune cells like macrophages present to CD4 cells

2. Exogenous process 3. Helper T-Cells

• MHC Antipresenting Cell Animations

Antigen Recognition and MHC restriction

EndogenousProcess

ExogenousProcess

Double Recognition and Activation Clonal selection – T-cells must accomplish

double recognition

Figure shows a CD8 cell becoming activated by Class I MHC protein (antigen fragment on its surface)

Cloning process forms TC Cells

Activation of T-Cells1. Antigen Binding

2. Co-stimulation occurs after antigen APC or body cell encounters the T-cell•Step before cloning •T-Cell must bind to other surface receptors on APC

• B7 protein of dendritic cells

•IL – I and II (cytokines)• Released by T-cells or APCs prompt cloning to start • Other Cytokines (Table 21.4)

Specific Roles of T Cells

1. Helper T cells

2. Cytotoxic T Cells (killer T cells)

3. Suppressor T Cells

4. Gamma Delta T Cells ▫T Cell

Animationshttp://highered.mcgraw-hill.com/sites/0072943696/student_view0

5. Regulatory T-Cells

• Immune Response

• Immune Response to Specific Pathogens

Primary Immune Response

Imbalances and Diseases 1. Severe Combined Immunodeficiency 2. AIDS– HIV

3. Autoimmune Disorders – MS

– Graves disease

– Lupus

– Rheumatoid Arthritis