Innate Immunity Overview

Innate Immunity

• Immunity types include innate resistance (natural barriers and inflammatory response) and adaptive (acquired) immunity.
• Lines of defense include the first line (natural barriers), second line (inflammation), and third line (adaptive immunity).
• First line of defense consists of physical and mechanical barriers like skin, low temperature/pH of skin, linings of GI, GU, and respiratory tracts, and biochemical barriers (e.g., antibacterial peptides in mucus, perspiration, saliva, tears).

First Line of Defense

• Physical barriers include skin and low temperature/pH of the skin.
• Mechanical barriers include linings of GI, GU, and respiratory tracts, sloughing off of cells, coughing, sneezing, vomiting, urinating, and mucus and cilia.
• Biochemical barriers include substances that trap or destroy microorganisms, as well as antibacterial peptides in mucus, perspiration, saliva, tears, and earwax.

Second Line of Defense: Inflammation

• Causes include infection, mechanical damage, ischemia, nutrient deprivation, temperature extremes, and radiation.
• Functions include preventing and limiting infection, controlling inflammation, and preparing the area for healing.
• Characteristics of inflammation include rapid initiation and no memory cells, as well a cardinal signs like redness, heat, swelling, pain, and loss of function.
• Vascular response involves blood vessel dilation and increased vascular permeability, with WBC adherence to vessel walls and migration through vessels.
• Plasma protein systems play a role in inflammation, including complement (destroying pathogens directly), clotting (forming a mesh to stop bleeding and prevent infection), and kinin systems.

Cellular Responders in Inflammation

• Cellular mediators include Mast cells, granulocytes (neutrophils, eosinophils, basophils), monocytes, macrophages, natural killer cells, lymphocytes, and cellular fragments (platelets).
• Biochemical mediators originate from destroyed cells and modulate activity of other inflammatory cells.
• Pattern Recognition Receptors (PRRs) recognize pathogen-associated molecular patterns (e.g., Toll-like receptors (TLRs)).

Phagocytosis

• Key cells involved include neutrophils, macrophages, and eosinophils.
• Functions include ingestion and disposal of foreign material and bacteria, dead cells, and macrophages.

Manifestations of Inflammation

• Local signs include heat, redness, swelling, pain, and loss of function. Systemic signs include fever, leukocytosis, and increased plasma protein synthesis.
• Types of exudates include serous (watery), fibrinous (thick clotted), purulent (pus), and hemorrhagic (containing blood).
• Chronic inflammation lasts two weeks or longer and is caused by unsuccessful acute response, microorganisms, toxins, and irritants. Characteristics include dense infiltration of macrophages and lymphocytes, as well as granuloma formation.

Wound Healing

• Wound healing stages include inflammation, reconstruction (begins 3–4 days post-injury), and remodeling (scar formation).
• Types of wound healing are primary intention (minimal tissue loss) and secondary intention (significant tissue replacement).
• Dysfunctions can include ischemia, hemorrhage, hypovolemia, infection, malnutrition, and medications, resulting in conditions such as Keloids, contractures and dehiscence.

Adaptive Immunity

• Adaptive immunity is characterized by recognizing foreign substances, providing long-term protection, and having memory.
• Key components include T cells (cellular immunity) and B cells (humoral immunity), along with antibodies (immunoglobulins—IgG, IgA, IgM, IgE).

Hypersensitivity Reactions

• Types of hypersensitivity reactions include Type I (IgE-mediated), Type II (tissue-specific), Type III (immune complex-mediated), and Type IV (T-cell-mediated).

Autoimmunity and Alloimmunity

• Autoimmunity involves the immune system attacking self-antigens (e.g., lupus).
• Alloimmunity involves a reaction against beneficial foreign tissues (e.g., transplants, transfusions).

Immune Deficiencies

• Types of deficiencies include primary (congenital) and secondary (acquired).

Chronic Inflammation

• Characteristics include dense infiltration of lymphocytes and macrophages, and granuloma formation

Active vs. Passive Immunity

• Active immunity is acquired through natural exposure (e.g., infection) or immunization (e.g., vaccination), resulting in long-term immunity.
• Passive immunity involves transferring preformed antibodies or T lymphocytes from a donor to a recipient (e.g., maternal antibodies to a fetus), leading to temporary immunity.

Types of Antibodies

• IgE is involved in allergies and parasitic infections.
• IgM is the first responder in infections.
• IgG provides long-term immunity and can cross the placenta.
• IgA is found in secretions (e.g., saliva, tears, breast milk).

Antigen Presenting Cells (APCs)

• APCs include dendritic cells, macrophages, and B lymphocytes.
• Their function is to process and present antigens to T-helper cells.