Key Points of Immune Responses

Two main types:
- Humoral Immunity (B lymphocytes, antibodies)
- Cell-Mediated Immunity (CMI) (T lymphocytes)

B cells produce antibodies; specifically, plasma cells secrete antibodies.
Antibodies mark antigens for destruction, but do not destroy directly.
Differentiation based on antigen location:
- Extracellular antigens: Activate humoral immunity.
- Intracellular antigens: Activate CMI.

Characteristic	Description
Structure	Pentamer when secreted (10 antigen-binding sites); monomer on B cell surface.
Location	Found in blood and lymph; also on the surface of B cells.
Abundance	~5-10% of total serum immunoglobulins; first antibody produced in a primary immune response.
Function	Potent agglutinator, highly effective in activating the complement system, marks extracellular pathogens for destruction.

Characteristic	Description
Structure	Monomer (2 antigen-binding sites).
Location	Most abundant Ig in serum (~80% of total serum Ig); found in blood, lymph, and intestines; capable of crossing the placenta to provide passive immunity to the fetus.
Abundance	~80% of total serum immunoglobulins; main antibody of secondary immune response.
Function	Neutralizes toxins and viruses, enhances phagocytosis (opsonization), triggers ADCC, and activates the complement system.

Characteristic	Description
Structure	Dimer in secretions (4 antigen-binding sites, held by a J chain and secretory component); monomer in serum.
Location	Predominant Ig in secretions (mucus, tears, saliva, breast milk, gastrointestinal and genitourinary tracts) where it protects mucous membrane surfaces; also found in blood and lymph (~10-15% of total serum Ig).
Abundance	~10-15% of total serum immunoglobulins.
Function	Prevents microbial attachment to mucous membranes, neutralizes toxins and viruses locally, provides local immunity.

Characteristic	Description
Structure	Monomer (2 antigen-binding sites).
Location	Primarily found on the surface of naive B cells, acting as a B cell receptor; very low concentration in serum (<0.2% of total serum Ig).
Abundance	Less than 0.2% of total serum immunoglobulins.
Function	Acts as an antigen receptor on B cells, signaling B cell activation.

Characteristic	Description
Structure	Monomer (2 antigen-binding sites).
Location	Primarily found bound to mast cells and basophils in tissues; very low concentration in serum (least abundant serum Ig).
Abundance	Least abundant Ig in serum.
Function	Mediates allergic reactions (e.g., binds to mast cells and basophils, triggering histamine release upon antigen binding) and plays a crucial role in defense against parasitic worms.

Antibody functions in immune response (general overview):
- Agglutination: Clumping of antigens, facilitating phagocytosis.
- Opsonization: Coating antigens to enhance phagocytosis.
- Neutralization: Blocking pathogen attachment and action.
- ADCC (Antibody-Dependent Cell-Mediated Cytotoxicity): Targets parasitic worms and virally infected cells, activating effector cells like eosinophils, NK cells, and macrophages.

T cells mature in the thymus; five types:
- Helper T cells (Th): Activate other immune cells.
- Cytotoxic T cells (Tc): Destroy infected cells on contact.
- Regulatory T cells (Tr): Suppress immune response to prevent autoimmunity.
- Delayed Type T cells (Td): Cause delayed reactions such as hypersensitivity.
- Memory T cells: Provide quicker response upon re-exposure to antigens.
CMI targets intracellular pathogens by recognizing processed antigens on cell surfaces.

APCs (Antigen Presenting Cells): Include dendritic cells and macrophages, present processed antigens to T helper cells.

Primary Response: Initial response to antigen, slower, produces memory B cells and IgM first, then IgG.
Secondary Response: Faster due to memory B cells; produces IgG first, higher antibody levels than primary response.

Vaccinations stimulate primary immune response, creating memory for faster future responses.
Continuous review of immune processes is necessary for retention of knowledge.