Acquired Immunity

Innate Immunity - 2nd & 3rd Lines of Defence

Recall of Knowledge

• Three lines of defence:

  • First line of defence: physical barriers and the immune system defend the body against pathogens.

  • Second line of defence: innate immunity.

  • Third line of defence: specific immunity.

• Four aspects of the first line of defence:

  • Skin

  • Mucous membranes

  • Natural secretions

  • Normal flora

Review - Inflammation – 2nd Line of Defence

• Pathogen stimulates an increase in blood flow to an infected area.

• Blood vessels in the area expand.

• White blood cells leak into the tissue from the vessels to invade the infected tissue.

• WBCs (phagocytes) engulf and destroy bacteria.

• Causes a red, swollen, painful inflammatory response.

Innate (Nonspecific) Immunity

• Phagocytosis process:

  1. The pathogen interacts with phagocyte receptors.

  2. Phagocyte engulfs the pathogen.

  3. Phagosome forms.

  4. Lysozyme digests the pathogen.

  5. The pathogen breaks down into proteins and other molecules.

  6. Antigen-presenting cell presents the antigen using the Major Histocompatibility Complex (MHC).

• Contrast with Adaptive (Specific) Immunity.

Review - Fever – 2nd Line of Defence

• Increased temperatures enhance immune cell functions.

  • Enhances phagocytosis.

  • Reactive oxygen species production by neutrophils.

  • Enhanced function of natural killer cells, T-helper cells, and antibody-producing cells.

• Fever can induce heat-shock proteins in both pathogens and host cells.

Third Line of Defence: Specific Immunity

• Specific defence processes are the immune responses specifically designed to combat particular microorganisms.

Specific Defenses

• The immune system forms a chemical “memory” of the invading microbe.

• If the microbe is encountered again, the body reacts quickly with few or no symptoms.

• Specific defences give us immunity to certain diseases.

Major Players in the Immune System

• Macrophage

• T cells (helper, cytotoxic, memory)

• B cells (plasma, memory)

• Antibodies

Vocabulary

• Antibody: a protein produced by the human immune system to tag and destroy invasive microbes.

• Antibiotic: chemicals produced by certain soil microbes that are toxic to many bacteria; some are used as medicines.

• Antigen: any protein that our immune system uses to recognize “self” vs. “Not self.”

Antibodies

• Antibodies are assembled out of protein chains.

• The immune system assembles different chains in different ways to make different antibodies.

Humoral vs. Cell-Mediated Immunity

• Humoral immunity produces antigen-specific antibodies and is primarily driven by B cells.

• Cell-mediated immunity does not depend on antibodies for its adaptive immune functions and is primarily driven by mature T cells, macrophages and the release of cytokines in response to an antigen.

B-Cells

• B-cells produce antibodies.

• B-cells with antibodies that bind with the invader’s antigen are stimulated to reproduce rapidly.

• B-cells differentiate into either plasma cells or memory B-cells.

  • Plasma cells rapidly produce antibodies.

  • Memory cells retain the “memory” of the invader and remain ready to divide rapidly if an invasion occurs again.

Clonal Selection

• Invading antigens bind to antibodies on one B cell.

• The B cell