The Immune System

Function

• The immune system functions to provide protection from disease causing agents in the one’s environment

• Pathogens include viruses, bacteria, fungi, protistans, and various parasitic animals

Lines of Defense

Innate Immunity – non-specific through a variety of mechanisms

1. Surface Barriers2. Internal DefenseAcquired Immunity – specific

through special lymphocytes1. Humoral Response – B Cells2. Cell Mediated Response – T Cells

Innate Immunity:Surface Barriers

• Skin with low moisture, low pH, thick layers of dead cells, and resident bacterial fauna

• Mucous membranes with low pH, lysozyme, and flushing action of secretions

Innate Immunity:Internal Defense

• The internal defense mechanisms of the innate immune response has a number of components, that may act in concert to defeat the foreign pathogen.

1. Phagocytic cells

2. Complement proteins

3. Inflammation

4. Natural Killer Cells

http://www.muhealth.org/~pharm204/inflammation.mov

Inflammation

In reaction to tissue damage or cell death mast cells release histamine which induces dilation in the surrounding capillaries and indirectly the four symptoms of inflammation:

1. Swelling2. Reddness3. Warmth4. Pain

Phagocytic Cells

There are a variety of phagocytic cells that include:

• Neutrophils• Eosinophils• Basophils• Macrophages

Compliment Proteins

• Actived plasma proteins create a Cascade of other proteins to form that produce pore complexes that induces lysis and death in cellular pathogens

• Bound complexes also promote phagocytosis

Acquired Immunity

• Becomes activated as physical barriers and inflammation fail. Phagocytic cells produce cytokines that initiate the acquired immune response.

• Specialized lymphocytes called B and T-cells initiate the humoral and cell-mediated responses, respectively.

General Mechanism

Pathogens stimulate the mitotic production of:

Effector cells that reduce the pathogen

• Helper T Cells• Cytotoxic T Cells• B CellsMemory cells that

remain in prepared for later infections by the same pathogen

Antigen Presentation

In this process macrophages

1. engulf, 2. process, and3. presents the

pathogens antigens in their MHC markers (surface proteins) to the immune system.

Helper T-Cells

• Antigen presentation activates Helper T-Cells which subsequently are involved in activating Cytotoxic T-Cells and B-Cells.

Cytotoxic T-Cells: Cell Mediated Response

• T-cells mature in the Thymus and take residence in the lymphatic system at maturity

• Effector Cytotoxic T-cells secrete

1. Perforins (pore producing chemical) and

2. Apoptosis inducing chemicals

B-Cells: Antibody Response

• B-cells mature in the bone marrow

• Effector B-cells secrete a diversity of “Y” shaped proteins called antibodies binding

• Antibodies bond to antigens and set them up for destruction by macrophages