Innate and Acquired Immunity

• Animals have naturally occurring nonspecific defense mechanisms against pathogens.
• Complex interactions occur among different types of immune cells and cellular secretions targeting specific pathogens.

Two Main Mechanisms:

• Innate immunity is non-specific and consists of disease-resistance mechanisms not specific to a particular antigen.
• Acquired immunity is specific with a high degree of specificity and memory.
• Innate immunity serves as the first line of defense, backed up by acquired/adaptive immunity.

Overview of the Immune System:

• The immune system is divided into innate and adaptive immunity.
• Innate immunity provides an immediate response to a wide array of substances.
• Adaptive immunity provides a delayed response to specific antigens.

Innate Immunity components:

• Skin and mucosal membranes/barriers prevent entry.
• Nonspecific internal defenses include cells such as macrophages and NK cells.
• Chemicals, like interferon and complement, contribute to innate immunity.
• Physiologic responses, such as inflammation and fever, are part of innate immunity.

Adaptive Immunity components:

• T-lymphocytes mediate cell-mediated immunity.

• B-lymphocytes mediate humoral immunity.

• Plasma cells synthesize and release antibodies.

• Microbial invasion triggers both innate and adaptive immunity.

• Innate immunity recognizes pathogens (PAMPs) and tissue damage (DAMPs), leading to inflammation and pathogen elimination.

• Adaptive immunity involves antigen capture and processing, T or B cell activation, immunologic memory, and pathogen elimination.

Innate Immunity Quick Comparison:

• Pattern-recognition receptors are part of innate immunity.
• Cellular components include neutrophils, macrophages, mast cells, lymphoid cells, basophils, and eosinophils.
• Humoral components include the complement system, natural antibodies, acute-phase proteins, antimicrobial peptides, and soluble lectins.
• The response is immediate, nonspecific, and not enhanced by multiple exposures.

Adaptive Immunity Quick Comparison:

• Diverse antigen-binding receptors are part of the adaptive immunity.
• Cell-mediated components include antigen-presenting cells (dendritic celles), T cells, and B cells.
• Humoral components include the complement system and immunoglobulins
• The response is slowly developing, highly specific, and enhanced by repeated exposures.

Innate Immunity details:

• Innate immunity is rapid, nonspecific (or generic), and present at birth.
• It is critical to defense but does not guarantee protection.
• Innate immunity lacks flexibility to respond to diverse microorganisms and may cause significant tissue damage.
• It activates within hours of antigen appearance.
• It does not require prior exposure to an infectious agent to be effective.
• Innate immunity has anatomic, physiologic, cellular, and chemical components.
• Innate immunity varies for each species.

Innate Immunity: Anatomic Mechanisms

• Unbroken skin
• Mucous membranes
• Hairs
• Cilia

Innate Immunity: Physiologic Mechanisms

• Temperature of Skin
• pH (stomach acid)
• Oils (sebum)
• Mucus
• Normal flora
• Sweat (lysozyme, salts, urea, and lactic acid)

Innate Immunity: Chemical Mechanisms

• Fever: inhibits replication of microbes and stimulates WBCs.
• Complement: 30 different inactive proteins in blood plasma.
  • Complements fight some fungi and bacteria in the blood.
• Interferons: glycoproteins released by cells.
  • Virus-infected cells producing interferon die, but the interferon attaches to surrounding cell membranes, preventing their infection.

Innate Immunity: Major Cellular Components

• They include Erythrocytes, Platelets, and WBC leukocytes such as Neutrophils, Eosinophils, Basophils, Monocytes and Macrophages, T-lymphocytes, and B-lymphocytes.

Innate Immunity: Cellular Mechanisms

• Inflammation.

• Phagocytosis.

• Cytokines released by blood and tissue aid swelling.

• Neutrophils arrive first, followed by monocytes and macrophages.

• Phagocytic cells must differentiate nonself to act on invading particles and dead/abnormal cells.

• Innate immunity is not long-lasting.

• Innate immunity does not induce immunological memory.

Acquired Immunity:

• Involves antibody specificity, diversity, memory, and self-nonself recognition.
• Acquired immunity is carefully regulated with sequential steps.

Acquired Immunity: Components

• Nonself-recognition involves proteins imbedded in the cell surface.
• Class I proteins found on almost all cells.
• Class II proteins found on specified cells for immune function.
• MHC/Major Histocompatibility Complexes are proteins.
• MHC is recognized by two molecule types: antibodies and T-cell receptors.
• APC’s stands for Antigen Presenting Cells

Adaptive Immunity: Humoral

• Involves extracellular processes
• Antigen-processing occurs in cells
• Antigen-sensitive cells are present
• Memory and antibody-producing cells

Acquired Immunity: Cells

• Lymphocytes are used - B and T types originate in bone marrow and develop into distinct types.
• B LYMPHOCYTE- act directly on cells (Humoral)
• T LYMPHOCYTE – act via activation mechanism to get killer cells to destroy foreign cells (Cell Mediated)

Lymphocytes: B cells

• Mature in bone marrow or lymphoid tissue of the gut.
• B-lymphocytes have antibody molecules on their surface, giving rise to plasma cells.
• Plasma cells actively secrete antibodies into the blood.

Lymphocytes: T cells

• Mature in the thymus gland.
• After maturation, each cell type migrates to precise areas in lymphoid tissue until needed.
• T-lymphocytes have surface receptors that bind antigens.

Acquired Immunity: B cells and Antibodies

• Antibodies are proteins called immunoglobulins.
• B lymphocyte produced to sensitize a specific antigen
• The B lymphocyte rapidly produces plasma cells and memory cells.
• Plasma cells can produce 2000 antibody molecules each second but only live a couple days.
• Memory cells have a longer life span than naïve B lymphocytes.

Major Immunoglobulin Classes in Domestic Mammals:

• Classes include IgM, IgG, IgA, IgE, and IgD.
• Molecular weights vary:
• IGM 900,000,
• IgG 180,000
• IgA 360,000,
• IgE 200,000,
• IgD 180,000.
• Subunits:
• IgM has 5,
• IgD, IgE, and IgG have 1,
• IgA as 2.
• Heavy chains are
• μ for IgM
• γ for IgG
• α for IgA
• ε for IgE
• 𝛿 for IgD
• Synthesized in:
• spleen and nodes (IgM, IgG, IgD)
• intestinal/respiratory tracts (IgA, IgE).

Acquired Immunity: Antibodies

• M is for macro with significant capacity to bind to the antigen (IgM)
• IgM is the first antibody produced in response to an antigen, circulates in blood, but is too large to cross the placenta.
• IgG is produced by time B memory cells and is most prevalent.
• IgG only crosses the placenta.
• IgA is found in mucous and serous secretions, providing local immunity, and is passed to young by nursing.
• IgD is found in plasma and is thought to suppress immune functions.
• IgE stimulates inflammation in parasitic/allergic conditions.

Acquired Immunity: T Cells

• T helper (TH or CD4): assists in immune response and produces B lymphocytes substances.
• Cytotoxic T cells (killer) creates pores in the foreign cell membrane to bind tighter.
• Suppressor T cells (CD8): Inhibits B Lymphocytes & Immune Response.
• Memory T cells stimulate faster response if the same antigen is present.
• Maturation of T lymphocytes must recognize foreign antigens, ignoring self antigens.
• T cells that do not achieve this with apoptosis will be killed within the thymus.

T Helper Cell:

• T Helper cells activate B Cells to create antibodies.
• T Helper Cells assist Macrophages and Killer T Cells to destroy foreign materials.

Tolerance:

• Immune system doesn't respond to a specific antigen in normal tissues.
• Tolerance directs against self-antigens in normal tissues.

Test your knowledge of immunology! Questions cover types of immunoglobulins and their role in inflammatory response & allergic reactions. Also covers roles of T cells, immunological tolerance, comparing innate and acquired immunity and innate immune mechanisms.