BIOLOGY OF HUMAN AGING

CHAPTER 10 CHAPTER 10

The Immune System

Outline Review of structure and function

Bone marrow/thymus/spleen/lymph nodes/tonsils/lymphocytes & plasma cells

Age related changesBone marrow/thymus/spleen/lymph nodes/tonsils

Age related dysfunctions General decrease in immune responses Age associated T-lymphocyte defects Acquired immune deficiency syndrome Lymphomas

Introduction People become more susceptible to disease as they

get older.

Immune system is a major defense against invasion of the body by microorganisms

Deficiencies of immune system make us more vulnerable to disease

Several facets of the immune response decrease with age

Review of Structure and FunctionBone Marrow•Located in central cavities of bones•Two types: yellow (fat deposit), red (hematopoiesis)

Thymus•Mass of lymphoid tissue•Located beneath the sternum•(consists of lymphocytes)

Spleen Largest lymphoid organ

Lies left of the stomach and extends upward to diaphragm

Composed of red pulp (blood sinuses and blood cells) and

white pulp (lymphocytes)

Filters the blood

Removes old, abnormal, or damaged RBCs

Lymph nodes Small masses of lymphoid tissue Located along lymphatic vessels Lymph enters the nodes and slowly filters through

the sinuses

Tonsils Small masses of lymphoid tissue embedded in the

lining of the pharynx and nasopharynx

Lymphatic System

Lymphatic and Immune System

Functions: Defends against infection: bacteria, fungi, viruses,

etc. Destruction of cancer and foreign cells. Synthesis of antibodies and other immune

molecules. Production of white blood cells.

Hematopoiesis: blood cell production

Development of T and B Lymphocytes

Third Line of Defense: The Immune Response (Specific Immunity)

Immunity: “Free from burden”. Ability of an organism to recognize and defend itself against specific pathogens or antigens.

Immune Response: Involves production of anti-bodies and generation of specialized lymphocytes against specific antigens.

Antigen: Molecules from a pathogen or foreign organism that provoke a specific immune response.

The Immune Response Destroys Specific Invaders

Antigen: Molecule that elicits an immune response.

“Antibody generating” Microbial antigens: Viral capsid, bacterial call wall, etc. Nonmicrobial antigens: Pollen, latex, food, etc.

Antibody: Protein found in blood plasma that attaches to antigen and helps counteract its effects.

Vaccination or Immunization: Process in which harmless forms of antigen or pathogen are introduced into body to provoke an immune response.

Lymphocytes Mount a Dual Defense1. Cell Mediated Immunity Immunity that requires cell to cell contact. Carried out by T cells:

Develop in the thymus. T cytotoxic cells: Important in defense against:

Cancer cells Self cells infected with fungi, viruses, protozoans, and

bacteria. T helper cells: Play a central role in immunity.

Act indirectly by controlling the immune functions of other cells:

Increased antibody production by B cells. Increased phagocytosis by macrophages. Increased killing of foreign and cancer cells.

T helper cells play a central role in immunity

Lymphocytes Mount a Dual Defense

2. Humoral (Antibody Mediated) Immunity Antibodies are found in our body fluids:

Blood Lymph Interstitial fluid

Antibodies are produced by B cells. B cells develop in bone marrow.

Antibodies are specific molecules that circulate through out our body and attach to foreign antigens, marking them for destruction.

Age-related changesBone Marrow• Reduction in the amount of active red bone marrow• Stem cells remain insufficient amounts to reproduce adequately

Thymus• Degeneration and reduction of size with aging • Lesser amounts of thymosins hormone produced (thought to be

responsible for the T cells differentiation)• Decrease in activity and numbers in Helper T cells• Increased number of immature T cells• Decreased activation of T cells• No change in total number of B cells, yet decline in antibody

production• Lower resistance to viral infections

Spleen• The average weight decreases. (animal studies!)• Lymphoid tissue gradually diminishes after puberty.• The nodes of older individuals contain more macrophages.

Lymph Nodes• Lymphoid tissue maximum development during childhood,

gradually diminish after puberty

Tonsils• Tend to decrease in size with age (palatine/pharyngeal tonsils).• Significant decrease in the lymphocyte number with age

Age-related Dysfunctions

General decrease in Immune Responses Reduction in cell mediated humoral immune responses Increased tendency for the development of autoimmune

reactions Diminished ability of the Abs to recognize Mutation of stem cells More suppressor cells or factors that inhibit immune

responses

Age-Associated T-Lymphocyte Defects: Reduced activity of T lymphocytes Reduced cell mediated immunity Reactivation of lymphoma, tuberculosis, and shingles

LymphomasSwollen lymph nodes, persistent fever, night sweats & weight lossClassification is based on patterns of spread, clinical behavior, and cells of origin

Acquired Immune Deficiency Syndrome

Immunodeficiency: depression of immune system and lack or insufficiency of immune responses

Helper T cells- CD4 Mode of transmission Dormancy Symptoms: generalized lymph node swelling, persistent

fever, night sweats, diarrhea, and severe weight loss AIDS-related complex: pneumonia and Kaposi’s sarcoma