immune system: from textbook PT2.

Natural Killer (NK) Cells
- Functions:
- Target abnormal cells like virus-infected or mutated cells.
- Recognize unusual markers on cell membranes recognized as foreign.
- Immediate destruction of identified abnormal cells.
- Effectiveness:
- Particularly effective against pre-cancerous cells and certain viral infections, including herpes.
- Comparison:
- Less selective than T-cells and B-cells regarding target identification.

Discuss the roles of different types of T-cells in providing cell-mediated immunity.
Describe the process of antibody-mediated immunity.
Differentiate between artificially and naturally acquired immunity with examples.
Distinguish between active and passive immunity with examples.

First Line of Defense: Non-specific innate defenses like phagocytes (e.g., macrophages).
Activation of Immune System:
- If innate defenses are overwhelmed, the immune system activates.
- Immune system has three key attributes:
1. Specificity: Targets only one antigen.
2. Memory: Creates immunological memory for faster responses in subsequent encounters with the same antigen.
3. Tolerance: Prevents immune cells from attacking healthy body tissues by recognizing self-markers.

Immune responses are focused on specific antigens unlike general non-specific responses.
Key immune cells: T-cells and B-cells
- Each cell recognizes only one specific receptor pattern.

After the first exposure to an antigen, the immune response builds memory, allowing quicker and stronger reactions on subsequent exposures to the same antigen.

Immunological Tolerance: The body’s immune cells ignore healthy self-cells while targeting non-self antigens.
Development of tolerance occurs during fetal development by deleting self-reacting lymphocytes.
Failure to achieve complete tolerance can lead to autoimmunity (autoimmune diseases).

Lymphocyte Composition:
- Comprises 20%-30% of circulating white blood cells.
- Types include NK cells, T-cells (majority), and B-cells.
Production Site:
- Both T- and B-cells are produced in bone marrow, but T-cells mature in the thymus.
- They carry antigen recognition molecules to detect and respond to specific antigens.

Hormone Thymosin: Promotes T-cell maturation, leading to the formation of specialized functional T-cells.
Specificity of T-cells:
- Each T-cell is programmed to react only to one type of antigen.
- Example: A T-cell for chickenpox will not respond to measles.
Function: Provides cell-mediated immunity.

B-cells originate and mature in bone marrow.
Function: Produce antibodies (immunoglobulins) targeting specific antigens.
Upon activation, B-cells enlarge and proliferate, producing:
- Plasma Cells: Secrete antibodies and are the main effector cells of the B-cell response.
- Memory B-cells: Long-lived cells providing rapid response for future encounters with the same antigen.
Activation: Requires helper T-cells to produce antibodies.

B-cells recognize antigens directly without needing presentation by antigen-presenting cells (APCs).
Each B-cell undergoes clonal expansion after activation.
Plasma Cells:
- Live less than a day, produce millions of antibodies specific to the activating antigen.
- Antibodies serve roles:
1. Bind and label antigens for destruction by other immune cells (e.g., macrophages).
2. Neutralize bacterial toxins.
3. Activate complement pathway.

IgA: Found in secretions like breast milk and saliva; prevents antigens from crossing epithelial membranes.
IgD: Functions in B-cell activation.
IgE: Associated with allergic responses; found on basophils and mast cells.
IgG: The most abundant antibody; crosses the placenta, providing fetal protection.
IgM: First antibody produced during primary response; strong activator of the complement system.

First exposure to an antigen leads to slow production of antibodies (mainly IgM), peaking 2-3 weeks later due to T-cell activation and B-cell proliferation.

Rapid and robust antibody production occurs during subsequent exposure, mainly IgG, which is more effective than IgM.
Reinforcements from memory cells enhance the immune response via booster vaccinations.

Active Immunity: Immunity that develops after exposure to an antigen, with T-cell and B-cell activation leading to memory cell production.
Passive Immunity: Conferred by the introduction of antibodies produced by another organism.

Naturally Acquired: Immunity from natural exposure to infections that creates memory cells.
Artificially Acquired: Immunity resulting from vaccination using weakened or killed organisms, or pathogen fragments.

Naturally Acquired: Antibodies passed from mother to fetus through the placenta or breast milk.
Artificially Acquired: Ready-made antibodies injected from recovered individuals or produced using recombinant DNA technology.

Non-specific defense cells accumulate at the infection site (neutrophils, NK cells, macrophages).
If needed, T-cells activate and proliferate to form cytotoxic and helper T-cells, thus activating B-cells.
B-cells differentiate into plasma cells, and antibody production commences, increasing immunity.

Includes: Anthrax, Cholera, Diphtheria, Hepatitis B, Measles, Mumps, Poliomyelitis, Rubella, Smallpox, Tetanus, Tuberculosis, Typhoid, Whooping cough.