1. Cytotoxic T cells
2. Helper T cells
3. Memory T cells
Innate immunity provides broad defenses against infection
Present before any exposure to pathogens and is effective from the time of birth
Involves nonspecific responses to pathogens
A pathogen that successfully breaks through an animal’s external defenses encounters several innate cellular and chemical mechanisms that impede its attack on the body
Non-selective and no lag time – immediate response, no previous exposure required
Protects against infections, toxins
Works with specific (acquired) immune response
Physical barriers, secretion, chemical toxins
Phagocytosis - macrophages neutrophils engulf and digest recognized "foreign" cells – molecules
Inflammatory response - localized tissue response to injury producing swelling, redness, heat, pain
Complement system – activated proteins that destroy pathogen plasma membranes
Natural Killer cells – special class of lymphocyte-like cells that destroy virus infected cells and cancer cells
Interferon - proteins that non-specifically defend against viral infection
Depends on B and T lymphocytes
Specific immune response directed attack against pathogens (antigen)
Previous Antigen exposure required
Protects against pathogens and cancer cells
Click here for an animation that summarizes the immune response. The animation is followed by practice questions.
- Phagocytes release chemical mediators
Adaptive (Acquired) Immune Response - 3rd line of defense
Properties of Acquired Immunity
Thymus – site of maturing T Lymphocytes
Lymph nodes – Exchange Lymphocyte w/ lymph (remove, store, produce, add). Resident macrophages remove microbes and debris from lymph. Lymphocytes produce antibodies and sensitized T cells released in lymph
Spleen – Exchange Lymphocytes with blood, residents produce antibodies and sensitized T cells released in blood, (worn RBCs)
Cell-Mediated Immunity – T Cells
Major types of T cells
Cell-Mediated Immunity – T Cells
Class I MCH molecules are found on almost all nucleated cells of the body display peptide antigens to cytotoxic T cells.
|Class II MHC molecules are located mainly on dendritic cells, macrophages, and B cells display antigens to helper T cells.|
1. A fragment of foreign protein (antigen) inside the cell associates with an MHC molecule and is transported
- Macrophages & Dendritic Cells engulf foreign antigens by phagocytosis, proteins broken down into peptides
T Cells Only Recognize Antigen Associated with MHC Molecules on Cell Surfaces
T Helper (TH) Cells
Cytotoxic T (Tc) Cells: Destroy target cells
- Can survive a long time and give lifelong immunity from infection
Antibody-Mediated (Humoral) Immunity
- 1000s of different B cells, each recognizes a different antigen on the surface of a macrophage.
- Antibodies or Immunoglobulins (Ig)
- Classes: IgG, IgM, IgA, IgE, IgD
Antibodies (immunoglobulins, Ig) are proteins that recognize specific antigens and bind to them. They are found in extracellular fluids (blood plasma, lymph, mucus, etc.) and the surface of B cells.
Defense against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells.
Antigenic determinants - specific regions of a given antigen recognized by a lymphocyte
Antibodies affinity: A measure of binding strength.
Consequences of Antibody Binding
B Cell Antibody Production
Secondary Response - Subsequent exposure to the same antigen displays a faster/more intense response due to the existence of memory cells, which rapidly produce plasma cells upon antigen stimulation
...B cells (and T cells) that encounter stimulating antigen will proliferate into a large group of cells.
Apoptosis- programmed cell death (“Falling away”).
- Human body makes 100 million lymphocytes every day. If an equivalent number doesn’t die, will develop leukemia.
Autoimmune Diseases: Failure of “Self-Tolerance”
- Some diabetes mellitus – attack beta cells
- First exposure: sensitization and activation clone B cells that form antibodies and memory cells
- Autoimmune diseases are a failure of self-tolerance
This material is based upon work supported by the Nursing, Allied Health and Other Health-related Educational Grant Program, a grant program funded with proceeds of the State’s Tobacco Lawsuit Settlement and administered by the Texas Higher Education Coordinating Board.