3.3 Basic community of immunity and inflammation

Basic Concepts of Immunity and Inflammation

Introduction to the Immune System

  • The immune system is a network of various leukocytes and proteins that work collaboratively to protect the host from invasion.

  • Essential for survival; it can distinguish between 'self' (the body) and 'nonself' (foreign substances).

  • Divided into two main divisions:

    • Innate Immunity: Immediate, non-specific response available from birth.

    • Adaptive (Acquired) Immunity: Develops over time after exposure to specific antigens (foreign substances).

Innate Versus Adaptive Immunity

Innate Immunity

  • Present from birth; does not require prior exposure to antigens.

  • Responds immediately and does not improve with repeated exposures.

  • Key Cells of Innate Immunity:

    • Neutrophils

    • Monocytes

    • Macrophages

    • Eosinophils

    • Basophils

    • Mast cells

  • Physical barriers (skin, mucosal membranes) play a crucial role in innate defenses.

Adaptive Immunity

  • Develops through life; antigen-specific and involves memory.

  • Requires a lag time to respond upon first exposure but provides a stronger response upon subsequent exposures.

  • Key Cells of Adaptive Immunity:

    • T-lymphocytes

    • B-lymphocytes

Primary Purpose of the Immune System

  • To defend an individual's life by identifying and combating foreign substances:

    • Deploys immune cells targeting invaders.

    • Produces biochemical substances to amplify the immune response.

    • This reaction to infection is referred to as host response.

The Immune Defense System

  • Infectious organisms invade through breaches in the body's barriers.

  • Categories of Threats:

    • Infectious organisms (bacteria, viruses, parasites).

    • Toxins from organisms or the environment.

    • Cancer, where normal cells transform into tumor cells.

    • Transplanted tissues from non-identical donors can also provoke immune responses.

Consequences of Dysfunctional Immune Function

  • Can be life-threatening:

    • Example: HIV disables key immune cells, leading to increased susceptibility to infections.

Consequences of an Overactive Immune Response

  • Can result in damaging effects:

    • Example: Rheumatic heart disease caused by the immune system's misdirected attack against heart tissue after Streptococcus pyogenes infection.

Components of the Immune System

Cells of the Immune System

  • Leukocytes (White Blood Cells):

    • Granulocytes: Include neutrophils, eosinophils, basophils, and mast cells (carry granules).

    • Agranulocytes: Include lymphocytes and monocytes/macrophages (lack granules).

Specific Cell Functions

  • Neutrophils:

    • Primary immune responders, most abundant.

    • Short-lived and contain bactericidal enzymes.

  • Eosinophils:

    • Combat parasitic infections and assist in allergic responses.

  • Basophils and Mast Cells:

    • Modulate allergic responses and release inflammatory mediators.

  • Monocytes:

    • Large phagocytic cells with a kidney-shaped nucleus, eventually transforming into macrophages in tissues.

  • Macrophages:

    • Larger leukocytes with extensive phagocytic activity, slower to arrive but crucial for antigen presentation.

  • Lymphocytes:

    • Three types: B-lymphocytes, T-lymphocytes, Natural Killer (NK) lymphocytes.

    • B-cells: Produce antibodies; T-cells help regulate immune responses.

Antibodies and Immunoglobulins

  • Structure and Function of Antibodies:

    • Y-shaped proteins with binding sites for antigens (Fab) and a constant region (Fc) for immune cell interaction.

  • Major Classes of Immunoglobulins:

    • IgG, IgM, IgA, IgD, IgE

IgG**

  • Most abundant and effective antibody; crosses the placental barrier.

IgM**

  • Largest antibody, first responder to initial antigens.

IgA**

  • Main defense at mucosal surfaces, transferred via breast milk.

IgE and IgD**

  • IgE: Involved in allergic responses.

  • IgD: Least understood.

How Antibodies Function

  • They coat targets to facilitate phagocytosis and activate the complement system, potentially triggering allergic reactions in sensitive individuals.

T-Lymphocytes

  • Four subsets:

    • T-helper cells (TH): Regulate immune responses.

    • T-cytotoxic cells (Tc): Attack virus-infected or cancerous cells.

    • T-memory cells (TM): Ensure a faster immune response upon re-exposure.

    • NKT cells: Act rapidly in immune defense against infections.

The Complement System

  • Composed of proteins that patrol the body and neutralize invaders.

  • Works synergistically with antibodies for pathogen neutralization.

Leukocyte Migration and Inflammatory Response

  • Chemotaxis: Leukocytes are attracted to infection sites due to cytokines released by tissue-resident cells.

  • Phagocytosis: Neutrophils and macrophages engulf pathogens.

Inflammation

  • Protective body response characterized by:

    • Dilation of blood vessels

    • Increased capillary permeability

    • Migration of leukocytes into tissues

  • Inflammatory mediators guide this response.

Major Events in Inflammatory Response

  1. Tissue damage triggers vascular response.

  2. Permeable capillaries allow fluid and cells into tissue.

  3. Phagocyte migration to inflammation site.

  4. Phagocytes destroy pathogens.

Acute Inflammation

  • Short-term protective process characterized by heat, redness, swelling, pain, and loss of function.

Chronic Inflammation

  • Can occur if the acute response fails; prolonged inflammation can lead to significant tissue injury.

Biochemical Mediators of Inflammation

  • Include cytokines such as IL-1, IL-6, TNF-α, which promote inflammation and increase vascular permeability.