intro to immunology

Role of Immune System

• The immune system functions to protect from disease.
• Immune system is made up of tissues, organs, cells, molecules, and genes.
• Immunology is a clinically important and evolving discipline.
• Therapeutic approaches target the immune system.

Immunology in Medicine

• Vaccines, antibodies, and cytokine therapy are all therapeutic approaches that target the immune system.
• Organ transplantation requires immune suppression.
• Allergen desensitization and adoptive cell therapy are also immunotherapies.

Microbes and Immune System

• Microbes are common in nature and have evolved to infect hosts and evade the immune system.
• Intracellular pathogens can include viruses, bacteria, and parasites.

The Challenges - Microbes

• Microbes exploit opportunities to infect hosts.
• Intracellular pathogens hijack cellular machinery to replicate and spread.
• Microbes are diverse and rapidly evolve to overcome host defenses.

The Defences - Physical and Chemical Barriers

• Physical barriers include skin, mucous membranes, and epithelial cells.
• Skin is a protective barrier that protects the underlying tissues.
• Mucous membranes trap pathogens and prevent them from invading the body.
• Cilia in the respiratory system move mucus and trapped pathogens.

Chemical Barriers - Antimicrobial Agents

• Chemical barriers include:
  • Stomach acid
  • Antimicrobial peptides (defensins)
  • Lysozyme
  • Digestive enzymes
• Antimicrobial peptides (defensins) disrupt the cell membranes of bacteria, fungi and viruses.

Immune Responses

• The immune system has two main types of responses: innate and adaptive.
• Innate immunity is immediate and provides a first line of defense.
• Adaptive immunity is specific to pathogens and requires exposure to activate.

Cells of the Immune System

• The immune system contains a multitude of different types of white blood cells (leukocytes).
• Leukocytes include neutrophils, macrophages, T cells, B cells, and others.

Innate Immunity

• Macrophages are phagocytes that patrol tissues.
• Macrophages are found throughout the body and there are numerous subsets with tissue-specific names (e.g., Kupffer cells in the liver).
• Neutrophils are the most abundant type of white blood cell in the blood.
• Monocytes are another type of agranulocyte present in the blood.

Phagocytosis

• Phagocytosis is the process of engulfment and internalization of particulate matter (e.g., pathogens).
• Phagocytosis forms a vesicle (phagosome) that contains the ingested material.
• Phagocytosis is an important mechanism to eliminate pathogens, cell debris, and damaged tissue.
• Opsonization is the coating of microbes with proteins (e.g., antibodies or complement) that facilitate phagocytosis.

Innate Immune Cell Summary - Phagocytes

• Phagocytosis is the primary function of:
  • Macrophages
  • Granulocytes (neutrophils, eosinophils, and basophils)
• Immature dendritic cells primary function is to activate the adaptive immune system.

Innate Cells - Neutrophils

• Neutrophils are granulocytes with multilobed nuclei.
• Neutrophils are typically not found in tissues but can be recruited to the site of infection.
• Neutrophils have a short lifespan after activation.

Innate Cells - Eosinophils

• Eosinophils are granulocytes found in low numbers in the blood.
• Eosinophils contain enzymes that attack the cell walls of parasites.
• kill antibody-coated parasites.
• role in allergic diseases.

Innate Cells - Basophils

• Basophils are granulocytes found in low numbers in the blood.
• Basophil granules contain potent inflammatory mediators that are important in the defense against parasites.
• allergic responses.

Innate Cells - Mast Cells

• Mast cells are granulocytes found in tissues.
• Mast cells, similar to basophils, contain potent inflammatory mediators and are involved in allergic responses.
• release of granules containing histamine and active agents.

Innate Cells - Natural Killer Cells

• Natural Killer (NK) cells are lymphocytes.
• NK cells kill host cells infected with viruses or cancer cells.
• NK cells produce chemical mediators called cytokines.

NK Cells Activation

• NK cells are activated by:
  • Antibodies
  • NKG2D ligands
  • Loss of MHC Class I molecules
• Antibody-dependent cell cytotoxicity (ADCC) is a process where NK cells kill antibody-coated cells via CD16.
• MHC Class 1 is a protein present on all nucleated cells that interacts with inhibitory receptors (KIR) on NK cells.
• MHC Class I is downregulated in viral infection and cancer cells.