Immune System

Chapter 43

What you need to know!

• Several elements of an innate immune response.

• The differences between B and T cells relative to their activation and actions.

• How antigens are recognized by immune system cells.

• The differences in humoral and cell-mediated immunity.

• Why Helper T cells are central to immune responses.

Organic, cellular, molecular componenets

• Lymphatic system: lymph ducts, lymph nodes, lymphatic organs (thymus gland, spleen, and tonsils)

• White blood cells: B-cells, T-cells, macrophages, and memory cells all mature from stem cells which originate in the bone marrow

• Protein factors: antibodies and antigens• Hormones: interferons and histamines

Antigen

• Protein or polysaccharide for cell recognition• Plasma membrane embedded surface protein• Antibody receptors (key-lock)• Very specific for each individual• About 20 in humans called major histocompatibility

complex (MHC)• MHC are genetically coded

Antibody

• Immunogen• Antigen receptors• Free circling in blood or attached on B-cell surface• Several classes IgA, IgD, etc.• Quaternary protein made of 2 light, and 2 heavy chains

Antibody Structure

First Line of Defense (barriers/non-specific)

• External barriers (skin) with antimicrobial substances (acidic pH)

• Mucus membranes lining the digestive, respiratory, excretory, and female reproductive system which constantly secrete mucus for the trapping and removal of unwanted substances• Cells are ciliated, cilia sway to keep mucus flow

outward• Chemical substances such as gastric juice which kills

most bacteria and viruses (exceptions include Hepatitis A)

Second Line of Defense (internal/nonspecific)

I. Phagocytes are amoeboid white blood cells; there are

many different kinds:• Neutrophils (60-70% of WBC): can leave the blood

stream to combat invaders; short life span (2 days)• Monocytes (5% of WBC): develop into macrophages• Macrophages: large, long-lasting destroyers, contain lots

of digestive enzymes for phagocytosis; permanent residents of your alveoli, liver, and lymph nodes

• Eosinophils: fight internal parasites• Natural Killer Cells: fight infected body cells (virus), and

precancerous cells

Second Line of Defense (internal/nonspecific)

II. Inflammation: Injuries are invasion sites for microbes

which trigger histamine release which causes:• Vasodilation (heat sensation)• Higher capillary permeability (WBC and platelets)• Release of prostaglandins (further inflammation)• Platelets begin blood clotting process• WBC fight invasion• Microbes releasing toxins trigger release of pyrogens

(fever)

Third Line of Defense:Specific Immune System4 characteristics:

1. Specificity: focus on specific invader

2. Diversity: response to variety of invaders

3. Self/non-self recognition: antigen identification

4. Memory: cells keep information about previous infection (memory cells)

Immunity includes:• Active immunity: acquired through past infections or

vaccinations• Natural passive immunity: mother passing antibodies

through placenta and breast milk• Artificial passive immunity: injection of immunoglobulins in

response to venom (snake bite)

Humoral Immunity – Antibodies:

1. B-cells have an antibody-studded surface

2. Foreign antigens bind to antibodies on B-cells

3. Antigen-antibody complex stimulation

4. Stimulated B-cell will produce/release this specific antibody as free floating antibody

5. Free floating antibodies will bind to all other antigens of the same type

6. Macrophages recognize antibodies and phagocytosis

7. Specialized B-cells become memory cells to prevent further attack from the same invader

Cell-mediated Immunity

1. T-cells have antigen recognition sites that are not antibodies

2. When binding to a foreign antigen, the T-cell will proliferate (reproduce) into helper T cells

3. Helper T cells identify pathogens to Killer T cells

4. Killer T cells use cytokines for apoptosis

Animation:• http://www.youtube.com/watch?v=1tBOmG0QMbA