The Lymph and Immune System

Defense Against Infectious Disease

Pathogens

• Defined as any living organism or virus that is capable of causing disease is called a pathogen

• Include– Viruses– Bacteria– Protozoa– Fungi– Various worms

The Lymphatic System

• Consists of two semi-independent parts– Lymphatic vessels– Lymphoid tissues and organs

• Lymphatic system functions– Transport fluids back to the blood– Play essential roles in body defense and resistance

to disease

The Lymphatic System

• Lymph – excess tissue fluid carried by lymphatic vessels

• Properties of lymphatic vessels– One way system toward the heart– No pump– Lymph moves toward the heart– Milking action of skeletal muscle– Rhythmic contraction of smooth muscle in vessel

walls

The Lymphatic System

• Lymphatic collecting vessels– Collects lymph from

lymph capillaries– Carries lymph to and

away from lymph nodes

Lymphatic Organs

• Several other organs contribute to lymphatic function– Spleen– Thymus (sweet breads)• thymosin

– Tonsils– Peyer’s patches

Preventing Pathogens from Entering the Body

• Non-Specific Immune Mechanisms– Skin• Primary outer defense• Dermis layer contains phagocytes

– Stomach acid• Acidic environment kills most pathogens

– Mucous membranes• Goblet cells create mucus and enzyme called lysozyme• Saliva and lacrimal glands produce lysozyme too

If/When Pathogens Get In: Specific (i.e., Immune System)

• Homeostatic Imbalance or Illness: Viral/Bacterial load exceeds the body’s ability to defend

• White Blood Cells (WBC’s/Phagocytic Leukocytes)– Macrophages are 1st line of defense• Identify “self” or “non-self” via protein identification

(antigens)• Called a non-specific response

Antibody Production

• Produced by B lymphocytes in response to a specific pathogen

• All pathogens have unique antigen combinations on the surface of their cells

• Antibodies are ‘Y’ shaped protein molecules that have binding sites for these specific antigens on the open end

• Antibodies bind to pathogen– Identifies it for disposal by body– Does not allow it to reproduce (bacteria) or bind to host cell

(virus)

Steps of Immune Response (vaccination/immunizations)

• 1. A specific antigen type is identified • 2. Specific B lymphocyte is identified that will produce an

antibody that will bind to antigen• 3. B lymphocyte and other identical B lymphocytes rapidly

clone themselves (mitosis) to increase lymphocyte count• 4. Lymphocytes begin antibody production• 5. Antibodies circulate in blood to find antigen match• 6. Antibodies attach and help eliminate pathogen• 7. Some antibodies remain in bloodstream and provide

immunity (memory cells)

HIV, AIDS and the Immune System

• Human immunodeficiency virus (HIV) has antigen binding site that binds to helper-T cells– Helper-T cells communicate via bloodstream as to

which cells need to undergo cloning in order to begin antibody production

• Without helper-T cells, antibody production cannot take place and no immunities develop

• Secondary infections cause Acquired Immunodeficiency Syndrome and eventual death

Types of Immunities• Active– Production of antibodies by

organism itself• Passive– Acquisition of antibodies

from another organism• Natural immunity– Immunity due to

infection/acquisition from mother

• Artificial– Due to vaccine

inoculation/antibodies

Antibiotics v. Bacteria and Viruses

• Antibiotics are chemicals that take advantage of the differences between prokaryotic and eukaryotic cells with respect to the chemical pathways within the cell– Some block protein synthesis in prokaryotic cells but

eukaryotic cells (yours)– Others inhibit bacterial cell walls

• For these same reasons, viruses are not affected because they utilized out eukaryotic cells for replication– Cytotoxic T-cells

• Destroy virus infected cells in the body– Interferon