1ST-SEM_IMMUNE_SYSTEM

Page 1: Overview of Immune System

Definition of Immune System

  • Immune Systems: Biological structures and processes within an organism that protect against disease by identifying and eliminating pathogens and tumor cells.

  • Function: Detects a wide variety of agents (e.g., viruses to parasitic worms) and distinguishes them from the organism’s own healthy cells and tissues.

Components of the Immune System

  • Organs, Tissues, Cells, & Cell Products: Integrated body system that differentiates self from non-self to neutralize potentially pathogenic organisms.

  • Distribution of Immune Cells:

    • Distributed in blood, lymph, epithelial layers, and tissues.

    • Arranged in spherical nodules called lymphoid nodules.

    • Present in mucosal tissues (e.g., digestive, respiratory, reproductive, urinary) known as MALT (mucosa-associated lymphoid tissue).

    • Organized into lymphoid organs: lymph nodes, spleen, thymus, bone marrow, etc.

Immune Cells

  • Key Cell Types:

    • White blood cells (e.g., phagocytes, lymphocytes)

    • Bone marrow

    • Lymph nodes

    • Tonsils

    • Thymus

    • Spleen

  • Antigen Exposure: Estimated that during a lifetime, individuals may encounter around a million foreign antigens, necessitating an equal number of lymphocytes to combat them.

Types of Immunity

  • Adaptive Immunity:

    • Natural Passive (maternal)

    • Active (infection)

    • Artificial Passive (antibody transfer)

    • Active (immunization)

  • Innate Immunity: Non-specific defense mechanisms present from birth.

Page 2: Central Immune Organs

Key Immune Organs

  • Bone Marrow: Site of origin for blood cells and immune cell progenitors.

  • Thymus:

    • Bilobed organ located above the heart, reaches maximum size during puberty (70g in infants; 3g in adults).

    • Site for T-cell maturation, with 95-99% of thymocytes undergoing apoptosis due to self-reactivity or non-reactivity.

    • Structure consists of cortex and medulla.

    • Rat thymocytes sensitive to glucocorticoids.

Other Associated Organs

  • Bursa of Fabricius: Site for B-cell maturation in birds (not present in humans).

Page 3: Functions and Processes in the Thymus

Function of the Thymus

  • Location: Anterior mediastinum, gradually enlarges during childhood, reduction in functioning mass post-puberty.

  • T-lymphocyte Education: Lymphoid cells undergo maturation and education before circulating.

Lymph Flow and Functions

  • **Lymphatic System:

    • Plasma seeps into tissue, interstitial fluid returns to circulation or becomes lymph.

    • Thoracic Duct: Largest lymphatic vessel, drains into left subclavian vein.

    • Movement relies on muscle contractions, one-way valves ensure directional flow.

  • Lymph Nodes: Act as filters for antigens with key immune functions:

    • Filtration of particles and microorganisms.

    • Activation and proliferation of B and T lymphocytes.

Spleen Functions

  • Largest accumulation of lymphoid tissue, containing abundant phagocytic cells for blood antigen defense.

  • Major site for aged erythrocyte destruction and activated lymphocyte production (blood filter).

Page 4: Additional Immune Components

Lymphoid Structures

  • Tonsils and Adenoids: (Waldeyer’s ring)

  • Peyer’s Patches: Located in the intestines.

  • Appendix and Large Intestine: Lymphoid aggregates.

  • **CD (Cluster of Differentiation) Markers: 300+ CD markers identified.

Immune Cells Types

  • B-Cells, T-Cells, Nk Cells:

    • T-cells (20-40% of leukocytes) express CD4 or CD8 markers.

    • Naïve T-cells have unactivated states.

Activation and Function

  • Cytotoxic T Cells: Kill infected cells with foreign antigens.

  • Helper T Cells: Stimulate other immune cells and produce cytokines.

  • Memory T Cells: Facilitate quick response on re-infection.

Page 5: T-Cell Development

Formation and Maturation of T-Cells

  • Origin: Formed in bone marrow & mature in thymus.

  • T-Cell Receptors (TCRs): Unique receptors recognizing antigens presented with MHC glycoproteins.

  • MHC Types:

    • MHC I on nearly all nucleated cells.

    • MHC II only on antigen-presenting cells (APCs).

T-Cell Subtypes

  • CD4+ T-Cells and CD8+ T-Cells:

    • Cytokines: Produced by T lymphocytes and monocytes to enhance T-cell performance against cancers.

  • B Cells: Differentiate into antibodies and neutralize antigens.

Antibody Classes

  • IgG, IgA, IgM, IgD, IgE:

    • Vary in function; IgG being the most common antibody type, central in pathogen binding and complement activation.

Page 6: Antigen-Presenting Cells (APCs)

Overview of APC Types

  • Include Langerhans and circulating Dendritic Cells (DCs).

  • Populating organs and specific areas of lymph nodes.

Function of APCs:

  • Responsible for presenting antigens to T cells.

  • Protect against intracellular and extracellular invaders.

Issues in Immune Response

  • Can cause hypersensitivity or autoimmune reactions if not regulated properly.

Immune System's Major Components

  • Innate Immunity: Primary defense against pathogens.

  • Adaptive Immunity:** Secondary defense; more specialized and systemic.

Page 7: Barriers to Infection

First Line of Defense Mechanisms

  • Skin: Acts as a physical barrier.

  • Mucous Membranes: Trap pathogens and destroy them (via various secretions).

  • Chemical Barriers: Includes microbial agents.

Mechanisms of Barrier Functionality

  • Antimicrobials in Skin: Fatty acids and lysozymes in sweat and saliva protect against pathogens.

Immune System Types

  • Innate (Nonspecific) Immunity: General defense mechanisms without memory.

  • Adaptive (Specific) Immunity: Specific antigen targeting with memory development.

Page 8: Antigen Recognition

Immune Response to Antigens

  • Key Points on Antigen Presentation:

    • Various immune cells are adept at distinguishing self from non-self.

    • Immune system memory and specificity allow effective pathogen response.

Immune Efficiency and Mechanism

  • Various components of the immune system work in harmony:

    • Antigen Detection to Elimination:

    • Involves activated immune cells, antibodies, and the cellular network.

Page 9: Clinical Assessment of Immune Function

Areas for Evaluation

  • Health History: Key indicators (age, immunization, allergies, diseases).

  • Physical Exam: Signs of infection or abnormal immune responses in various systems.

Special Considerations

  • Elderly Immune Function: Age-related immune decline can increase disease risk; chronic infections are more common.

Nutritional Impact on Immunity

  • Adequate intake of essential vitamins is vital. Poor nutrition can lead to immune dysfunction.

Page 10: Immune Function Tests

Standard Diagnostic Tests

  • Complete blood count, immunoglobulin levels, lymphocyte counts, and specific antibody responses to gauge immune health.

Additional Diagnostic Procedures

  • Bone marrow biopsy and skin tests may be utilized for comprehensive assessment.

Special Lab Procedures

  • Investigation of hypersensitivity, phagocyte function, and complement activity.

Page 11: Threats to Immune Function

Common Medical and Environmental Threats

  • Chronic diseases, infections, environmental toxins affecting immune responses.

  • Stresses, both physiological and psychological, can worsen immune function.

Page 12: Conclusion

Upcoming Trends in Immunology

  • Advances in immunotherapy and understanding of immune mechanisms hold promise for better treatments.

  • Preventive medicine and vaccination relevance continue to be major themes.