Ch. 7: The Immune System – Study Guide and Review

The Immune System

Overview of the Immune System

The immune system is a complex network of cells, tissues, and organs that work together to defend the body against infectious agents and other foreign substances. It is divided into innate (nonspecific) and adaptive (specific) immunity, each with distinct roles and mechanisms.

• Innate Immunity: The body's first line of defense, providing rapid but nonspecific responses to pathogens.

• Adaptive Immunity: A slower, highly specific response involving lymphocytes and the production of antibodiesiunctions of the Immune System

• Protection against pathogens (bacteria, viruses, fungi, parasites)

• Removal of dead or damaged cells

• Recognition and elimination of abnormal (e.g., cancerous) cells

Lymphatic System and Immune Function

• Primary lymphoid organs: Sites where lymphocytes are produced and mature (bone marrow, thymus)

• Secondary lymphoid organs: Sites where immune responses are initiated (lymph nodes, spleen, tonsils, MALT/GALT)

Components of the Immune System

• Cells: Lymphocytes (B cells, T cells, NK cells), phagocytes (macrophages, neutrophils), dendritic cells, etc.

• Molecules: Antibodies, cytokines, complement proteins

• Tissues: Lymphoid tissues (lymph nodes, spleen, MALT/GALT)

Lymphoid Tissues: MALT and GALT

• MALT (Mucosa-Associated Lymphoid Tissue): Lymphoid tissue associated with mucosal surfaces (e.g., respiratory, digestive tracts)

• GALT (Gut-Associated Lymphoid Tissue): Specialized lymphoid tissue in the gut (e.g., Peyer's patches)

Leukocytes: Types and Functions

Leukocyte	Location of cell	Function
Neutrophil	Blood, tissues	Phagocytosis of bacteria and debris
Eosinophil	Blood, tissues	Defense against parasites, allergic reactions
Basophil	Blood	Release of histamine, inflammation
Monocyte	Blood (precursor to macrophages)	Phagocytosis, antigen presentation
Lymphocyte	Blood, lymphoid tissues	Adaptive immunity (B and T cells), innate immunity (NK cells)
Dendritic cell	Tissues	Antigen presentation, activation of T cells

Lymphocyte Types (Stem Cell Derived)

Lymphocyte	Location of cell	Function
B lymphocyte	Bone marrow, lymph nodes	Produce antibodies (humoral immunity)
T lymphocyte (Helper, Cytotoxic, Regulatory)	Thymus, lymph nodes	Cell-mediated immunity, regulation of immune response
NK cell	Blood, tissues	Destruction of virus-infected and tumor cells

Phagocytosis

• Process by which phagocytes (e.g., neutrophils, macrophages) engulf and digest pathogens and debris.

• Essential for innate immunity and activation of adaptive responses.

Mechanisms of Defense

Mechanism	Category of Action	Function
Physical barriers	Innate	Prevent entry of pathogens (skin, mucous membranes)
Phagocytosis	Innate	Engulfment and destruction of pathogens
Antibody production	Adaptive	Neutralization and opsonization of pathogens
Cell-mediated cytotoxicity	Adaptive	Destruction of infected or abnormal cells

Antibody Structure and Function

• Structure: Composed of two heavy chains and two light chains, with variable (antigen-binding) and constant regions.

• Functions:

  • Neutralization of toxins and pathogens

  • Agglutination of antigens

  • Opsonization (enhancing phagocytosis)

  • Activation of complement system

  • Antibody-dependent cellular cytotoxicity (ADCC)

Major Histocompatibility Complex (MHC)

• MHC I: Present on all nucleated cells; present endogenous antigens to cytotoxic T cells.

• MHC II: Present on antigen-presenting cells; present exogenous antigens to helper T cells.

Types of Immunity

• Active Immunity: Immunity produced by exposure to an antigen (natural infection or vaccination).

• Passive Immunity: Immunity transferred from another source (e.g., maternal antibodies, antibody therapy).

Immune Responses to Infection

• Bacterial Infection: Involves phagocytosis, complement activation, and antibody production.

• Viral Infection: Involves cytotoxic T cells, NK cells, and antibody-mediated neutralization.

Self-Tolerance and Autoimmunity

• Self-tolerance: The immune system's ability to avoid attacking the body's own tissues.

• Autoimmunity: Failure of self-tolerance, leading to immune-mediated damage to self tissues.

Allergic Reactions and Hypersensitivity

• Allergy: An exaggerated immune response to harmless antigens (allergens).

• Types of Hypersensitivity: Immediate (Type I), cytotoxic (Type II), immune complex (Type III), delayed (Type IV).

Maternal-Fetal Immunology

• Potential immunological complications can arise between Rh- mothers and Rh+ fetuses, leading to hemolytic disease of the newborn (erythroblastosis fetalis).

Neuro-Endocrine-Immune Interactions

• The immune system interacts with the nervous and endocrine systems, influencing immunity and health through hormones, neurotransmitters, and cytokines.

Additional info: These notes are based on the structure and prompts of a study packet, with academic context and explanations added for completeness and clarity.