Immunity and Organs - Unit 1

Fundamental Functions of the Immune System

• Differentiates between SELF and NON-SELF entities.
• Classifies non-self entities into infectious (pathogens: viruses, bacteria, fungi, parasites) and non-infectious (food, pollen, dust).
• Recognizes infectious self (cancer) and non-infectious self (body cells and proteins).

Mode of Operation of the Immune System

• Identification: Distinguishes non-infectious self and infectious non-self.
• Recruitment: Mobilizes immune effectors.
• Elimination: Clears pathogens from the body.
• Prevent Recurrence: Establishes immunological memory to prevent future infections.
• Deactivation: Stops immune response to prevent collateral damage.

Types of Immunity

• Innate Immunity: Non-specific response, immediate maximal reaction, no immunological memory.
• Adaptive Immunity: Specific response, delayed maximal reaction, leads to immunological memory.
• Humoral Immunity: Mediated by macromolecules in body fluids.
• Cellular Immunity: Involves activation of phagocytes, T-lymphocytes, and cytokines without antibodies.

Components of the Immune System

• Innate Immune System

  • Non-specific, immediate response.
  • Present in nearly all life forms.

• Adaptive Immune System

  • Specific to pathogens, has a lag time for maximal response.
  • Found only in jawed vertebrates and induces immunological memory.

Surface Barriers

• Skin acts as a primary barrier against infections.
• Additional defenses include:
  • Gastric acid and proteases in the stomach prevent ingested pathogens.
  • Flushing actions of tears and urine expel pathogens.
  • Mucus in respiratory and gastrointestinal tracts traps microorganisms.
  • Enzymes like lysozyme serve antibacterial functions.

Commensalism

• A relationship where one organism benefits without affecting the other.
• Commensal flora can assist in nutrition, pathogen exclusion, and contribute to immune defense.
• Lactobacillus in the vagina inhibits other bacteria by reducing pH.

Organs of the Immune System

Primary Lymphoid Organs

• Bone Marrow

  • Source of all circulating blood cells and B cell maturation.
  • Contains red marrow (hematopoietic tissue) and yellow marrow (fat cells).

• Thymus

  • Located behind the sternum, responsible for T cell differentiation and maturation.
  • Contains thymic stromal and cortical cells which support T cell development.

Secondary Lymphoid Organs

• Lymph Nodes

  • Oval structures that filter lymph fluid, containing germinal centers for lymphocyte production.
  • Enclosed by a fibrous capsule, with afferent and efferent lymphatic vessels.

• Spleen

  • Largest lymphatic organ, filters blood, and contains red pulp (blood components) and white pulp (lymphatic nodules).
  • Plays a critical role in managing aged erythrocytes and immune responses.

• MALT (Mucosa-Associated Lymphoid Tissue)

  • Protects mucous membranes in areas such as the gut and respiratory tract.

Function of the Lymphatic System

• Provides defense against harmful organisms and chemicals through two types of defense: nonspecific and specific (immunity).
• Humoral immunity involves B cells which transform into plasma cells and produce antibodies.
• Cell-mediated immunity entails T cells that directly destroy infected cells.

Thymus Microenvironment

• Consists of thymic stroma and thymocytes, facilitating T cell development.
• The blood-thymus barrier protects immature T cells from foreign antigens.