The Immune System

Key Components of the Immune System

Major Components: The immune system consists of various components including circulatory and lymphatic systems, and lymphoid organs.

Circulatory and Lymphatic Systems

Lymphoid Organs:

  • Red bone marrow

  • Thymus

  • Lymph nodes

  • Spleen

  • SALT (skin-associated lymphoid tissue)

  • MALT (mucosa-associated lymphoid tissue)

  • GALT (gut-associated lymphoid tissue)

  • BALT (bronchus-associated lymphoid tissue)

  • Other associated tissues in the skin, mucosa, gut, and breast

White Blood Cells - Leukocytes

White blood cells are crucial for immune defense against pathogens.

First Line of Defense: Barriers

Physical Barriers include:

  • Skin

  • Hairs and sweat glands

  • Mucous membranes

  • Blinking and tears

  • Salivary flow

  • Secretions with lysozyme

  • Urination

  • Vaginal secretions

Key Terminology in Immune System

  • Antigens: Molecules like proteins or glycoproteins that can be recognized by the immune system as 'self' or 'non-self'.

  • PAMPs (Pathogen-Associated Molecular Patterns): Common antigens among microbes.

  • PRRs (Pattern Recognition Receptors): Receptors that recognize PAMPs on host cells.

  • MPS (Mononuclear Phagocyte System): Network of phagocytes in connective tissues.

Second Line of Defense: Phagocytosis and Inflammation

Phagocytosis Activities:

  • Survey tissue for microbes, debris, or dead cells.

  • Ingest and eliminate these materials, recognizing antigens.

Innate Immune System

Recognition of Pathogens: Recognized by innate immune system cells through PAMPs.

Mononuclear Phagocyte System

Specialized phagocytes are key players in the immune response.

Chemotaxis and Ingestion

PAMP Recognition: Phagocytes recognize PAMPs, serve as signal molecules enabling an immune response. Not present in mammals

Examples of PAMPs include peptidoglycan and lipopolysaccharides.

Pattern Recognition Receptors (PRRs)

Roles of PRRs:

Present on phagocytes and immune cells, found on the surfaces of phagoctyes, dendritic cells, endothelial cells, and lymphocytes these receptors recognize and bind PAMPs.

Toll-Like Receptors (TLRs) and Collectins

TLRs: A specific type of PRR responsible for initiating immune responses upon PAMP detection. A defensive response to pathogens.

Collectins: Exogenous proteins that assist in pathogen recognition, found in blood and tissues.

Destruction and Elimination Systems

Oxygen-Dependent System: Employs myeloperoxidase and other oxygen products (e.g., superoxide anion, lysozyme) for pathogen destruction.

Inflammation

Signs of Inflammation: Redness (erythema), swelling (edema), pain, heat.

Benefits of Inflammation:

  • Fluid influx dilutes toxins

  • Fibrin clots control spread of microbes

  • Neutrophils phagocytose pathogens and dead cells.

Chronic Inflammation

Characteristics: Subtle symptoms lasting months or years can damage healthy tissues, leading to diseases like cancer and diabetes.

Anti-inflammatory Foods: Foods rich in antioxidants can help mitigate inflammation (e.g., olive oil, leafy greens).

Third Line of Defense: Specific Immunity

Mediated by T and B lymphocytes for targeted immune response.

Key Characteristics of Specific Immunity:

Specificity: The immune response is tailored to specific antigens.

Diversity: The immune system can recognize a vast array of different antigens.

Inducibility: Immune responses can be initiated upon exposure to antigens.

Clonality: Activated lymphocytes proliferate to form clones that respond to the same antigen.

Tolerance: The immune system learns to tolerate self-antigens to prevent autoimmunity.

Memory: Following an initial exposure, long-lived memory cells enable a quicker response to subsequent exposures to the same antigen.

Stages of Immunologic Development

Stages include:

  • Antigen contact

  • MHC markers presentation

  • Antibody production by plasma cells and memory cells formation.

Characteristics of Antigens

Antigens must be perceived as foreign to invoke an immune response, and larger molecules are generally more immunogenic.

Epitope: The specific portion of an antigen that is recognized by lymphocytes.

Haptens: Small molecules that can become immunogenic when attached to carrier proteins.

Alloantigens

Proteins and other molecules of one person that are

antigenic to another

• Cell surface markers that occur in some members of the

same species but not in others

• The basis for an individual’s blood group and major

histocompatibility profile

• Responsible for incompatibilities that occur in blood

transfusion or organ grafting

Superantigens

Definition: Potent bacterial toxins that can activate T cells at an excessive rate, leading to an overwhelming immune response and potential severe outcomes.

Antigen Processing and Presentation

Process: Antigens must be processed and presented by antigen-presenting cells like macrophages and dendritic cells to activate lymphocytes.