IMMUNITY

What is Immunity? Ability of the body to protect itself from viruses, bacteria, and other disease causing agents The word immunity comes from the Latin word immunis meaning exempt

IMMUNE SYSTEM SPECIFIC response to foreign substances Substances that evoke the response are called ANTIGENS Immune response produces proteins that are specific to the antigen, these are ANTIBODIES Specific white blood cells called LYMPHOCYTES are produced

Types of Acquired Immunity Naturally acquired immunity Artificially acquired immunity

Naturally acquired immunity ACTIVE – exposure to antigen naturally in the course of daily life This is the type of immunity from having a disease PASSIVE – maternal antibodies transferred via the placenta or mother’s milk Temporary immunity for the newborn

Artificially acquired immunity ACTIVE – vaccination Receive antigen via injection of vaccine Produce antibodies against the injected antigen PASSIVE – preformed antibodies Receive preformed antibodies from immune person or animal Antiserum Temporary protection

Duality of Immune System Humoral immunity Production of antibodies B cell activation Active against bacteria, toxins, and viruses that are circulating in body fluids Cell-mediated immunity Activation of T cells Active bacteria and viruses that are inside host cells

What are Antigens? Things that are foreign to our body Usually proteins or large polysaccharides Antigenic determinants are often parts of the invading microbe Antibodies react with specific regions of the antigen called EPITOPES

Antigenic determinants

What are Antibodies? Antibodies are proteins React with only ONE specific antigen Neutralize or destroy the antigen Each antibody has specific antigen binding sites

Antibody structure Consists of 4 chains 2 light and 2 heavy chains Variable regions of antibody bind specific antigen

Antibody structure

Antibody variable regions (antigen binding sites)

Classes of Antibodies (Immunoglobulins) IgG IgM IgA IgD IgE

IgG Single unit monomer antibody 80% of all antibodies are of this class Crosses the placental barrier to protect fetus Protects against CIRCULATING bacteria, viruses, and toxins

IgM 5 monomer antibody 5-10% of antibody in serum First class of antibodies formed to antigen Reacts with human ABO blood groups Clumps the antigen

IgA 2 unit monomer antibody 10-15% of antibodies in serum Abundant in mucous membranes, tears, saliva, and breast milk Prevents pathogen attachment to mucosal surfaces

IgD Single unit monomer antibody 0.2% of serum antibody Found in blood and lymph Antigen receptor on B cells

IgE Single unit monomer antibody 0.002% of antibodies in serum Binds to mast cells and basophils Allergic reactions

B cells Develop in the bone marrow Migrate to lymph nodes and spleen Recognize antigen by cell surface receptors Activated B cells divide to form plasma cells which secrete antibody

Clonal Selection B cell is sensitized by specific antigen Divides to form many more identical cells (clones) The clones differentiate into plasma cells that secrete antibody formed against the antigen Some cells become memory cells to provide protection for years to come

Clonal Selection

Results of Antigen-Antibody Binding 1. Agglutination 2. Opsonization 3. Neutralization 4. Complement activation 5. Inflammation

Results of Antigen-Antibody Binding

Monoclonal Antibody Production

Uses of Monoclonal Antibodies Diagnostic kits Pregnancy testing Suppression of tissue rejection in transplants Disease treatment

Primary and Secondary Immune Response Primary response to antigen is by IgM antibodies IgG antibody production begins several days later Second exposure to antigen results in IgG production immediately and in large quantities Anamnestic (memory) response

Memory response

Cell-mediated Immunity Based on the activity of T cells T cells are a class of lymphocytes that are produced in the bone marrow but mature in the thymus gland Distributed in the various lymphatic organs Effective against intracellular antigens

What are Cytokines and Interleukins? Cytokines are the chemical messengers of the immune system Interleukins are the cytokines that serve as communicators between white blood cells There are now at least 26 different interleukins (IL) many of which have important functions in the immune system

T cells T cells are the key cellular component of immunity There are 4 main types of T cells T Helper cells* Cytotoxic T cells* Delayed hypersensitivity T cells Suppressor T cells

CD – no not compact discs (Cluster of differentiation) T cells carry surface receptors called CD’s that are used to differentiate between the various types of T cells T helper cells are classified as CD4 cells by their receptor Cytotoxic T cells are CD8 cells

T Helper cells Key cell that activates cell-mediated immunity and links humoral (antibody) immunity to cell-mediated immunity The T helper cell is attacked and destroyed by the AIDS virus leading to immune system failure

T - helper cells and HIV Time course

Helper cell activation Antigen is presented to the helper cell by another cell called an APC cell APC cell and T helper cell bind APC cell secretes IL-1, T helper cell is now activated! IL-1 simulates the T helper cell to secrete IL-2 IL-2 secretion stimulates the activated T(H) cell to form clones of itself and also to stimulate other cells such as B cells to make antibody, and T(C) to attack infected cells

T helper cell activation

Cytotoxic T cells Once activated by the T(H) cell the T(C) seek out and destroy infected cells in the body The T(C) bind with infected cells and release PERFORIN that causes the infected cells to burst (lyse)

Cytotoxic T cell activity

How the Cytotoxic T cells works

T cell/B cell interaction

T cell/B cell interaction

Immune system summary

Summary of cell-mediated immunity APC’s stimulate the T(H) cell The T(H) cell is central to both humoral and cell-mediated immunity T(H) cells stimulate B cells to make antibody and cytotoxic T cells to destroy infected cells Without T(H) both aspects of immunity will fail and so will you!