Immunity

Anatomy & Physiology

Tony Serino, Ph.D.

Biology Department

Misericordia Univ.

Immune System• Provide defense of the body against

infectious agents, toxins, foreign bodies, and cancers

• Two types of defenses:– General (Non-specific or Innate) Defense

• Barriers• Normal Flora and Fauna• Fever• Surveillance• Inflammation• Non-specific Phagocytic WBCs and NK cells• Protective Chemicals

– Specific (Adaptive) Defense --Lymphocytes

Barriers• Prevent infectious agents from penetrating

internal environment– Epithelium ( thickness, tight junctions, keratin)

-especially the skin– Cilia and mucus– Watery secretions (tears, saliva)– Acidity (stomach, urine, vaginal secretions)

• Normal Flora and Fauna –resident bacteria prevent infectious agents from growing on body surfaces

Fever

• Rise in Body Temperature

– Inhibits invading cell growth; increase body metabolism to increase defense/repair cell activity

– Produced by release of pyrogens from leukocytes– Low grade fever is beneficial in fighting infection,

high sustained fever may be life threatening

Surveillance

• Number of cells and organs to detect invading agents

• Langerhans cells of skin, Mast cells, Dendritic cells, and organs like: Tonsils, GALT cells

• Gather antigens and present them to lymphocytes

Inflammation• Allows more blood defenses into damaged areas• Triggered by release of paracrines from

damaged tissues (PG), attacking WBCs (cytokines), mast cells (heparin and histamine), and activation of blood protective chemicals (complement and bradykinins)

• Increases: – blood flow through vasodilation (hyperemia)– capillary permeability– Both lead to local edema

• If prolonged or systemic, can become life threatening

Inflammatory Response

Phagocytic WBC and NK cells• WBCs can distinguish the sugars in

mammalian cells and those found on bacteria or other parasites– PMNs, macrophage, and mast cells can injure

or destroy cells that do not display normal sugars

• NK cells –related to T-cells but attack any cell not displaying MHC I proteins– Kill by secreting perforins and other chemicals

Phagocytosis

Protective Chemicals

• Chemicals that aid in destroying or retarding infectious agents– Interferon –cytokine released when cell

attacked by virus; warns other cells in area– Lysozyme –antibacterial enzyme present in

tears and saliva– Complement –blood proteins which can detect

and destroy bacteria

Interferon

MAC –membrane attack complex (C3-C9)

Complement

Specific (Adaptive) Immunity• Individual targets are selected for attack by the

lymphocytes that can bind that target (antigen)• Antigens (Ag) – any large substance not normally

found in the body; these illicit an immune response (immunogenic and immuno-reactive)

• Haptens are small molecules that can trigger an immune response only if bound to larger molecules (like: pollen, some cosmetics, detergent fragrances, poison ivy animal dander and drugs); they are immuno-reactive but not immunogenic by themselves

Antigenic DeterminantsLarge macromolecules illicit immune response because they have many sites to which immune molecules will attach; proteins have the most of any molecule

Identifying “Self” from “Non-self”• T-cells migrate to thymus, B-cells remain in bone

marrow (the primary lymphoid tissues)• Become immunocompetent -selected for their

ability to produce a surface receptor against an antigen and to tolerate self antigens

• Those that bind weakly to self-antigens are selected, the others are eliminated

• The strongest self-antigens are the MHC proteins• Once competent, the cells are released to move

through the blood and aggregate in the secondary lymphoid tissues

Thymic Selection

Movement of Lymphocytes

Cells Involved in Specific Immunity• Lymphocytes (B and T cells) -attack antigen

bearing agents either chemically (humoral immunity –the B-cells) or physically (cellular immunity –the T-cells)

• T and B-cell activation to an antigen works best when they are presented with the antigen by another cell

• APCs (Antigen Presenting Cells) (macrophage, surveillance cells, B-cells, infected cells) display foreign antigenic determinants on their MHC II cell surface proteins to activate the lymphocytes

Memory T cell

B-cell Clonal Expansion

Antibody Structure

Antibody Actions

Opsonization –Ag-Ab complex makes ID for phagocytosis easier

Humoral Response

Control of Lymphocyte Response• B-cells can be activated by the antigen alone, but

it is more effective if they are presented the antigen by APCs or stimulated by T-helper cells

• Activation of T-helper cells stimulates complete lymphocyte response

MHC I –found on all body’s cells except RBCsSurface proteins usually bound to pieces of intracellular proteins, but when infected they present fragments of the infectious agent

MHC II –found on APCs-bound to phagocytized outer coat molecules of immuno-agent

T-cell Types

Helper T-cells

Clonal Selection of T-cell

Cytotoxic T-cell Attack

Primary Immune Response

Vaccine Production

Types of Acquired Immunity

Acute Allergic Reaction

Pathologies• AIDS –HIV invades T-helper cells, diminishing

effectiveness of immune response; may have as long as 8 year incubation time, 100% fatal

• Autoimmune Diseases –Immune system targets naturally occurring compounds of the body (usually sequestered proteins) MS, rheumatoid arthritis, Diabetes mellitus (I), etc.

• Cancer –cancers cells spontaneously form during life, but the immune system keeps them in check; failure results in tumors and metastasis