Immunology: Adaptive vs Innate Immunity

Adaptive Immunity

• Specific for antigens that may be microbial or non-microbial, not essential for survival
• May differ among microbes of the same type
• Microbes can evade adaptive immunity by mutating the antigens recognized by lymphocytes

Innate Immunity

• Recognizes structures that are shared by microbes, but not present on host cells
• Cannot be evaded by microbes
• Components:
  • Intact skin (physical barrier)
  • Phagocytes (Neutrophils, Monocytes, Macrophages)
  • Natural killer (NK) cells
  • Soluble factors (e.g. Interferons, Lysozyme, Acute phase proteins, Complement)
  • Cytokines of innate immunity

Phagocytes

• Types: Neutrophils, Monocytes, Macrophages
• Function: Recognize and ingest microbes for intracellular killing
• Neutrophils:
  • Most abundant leukocytes in the blood (4000-10,000/mm3)
  • Called polymorphonuclear leukocytes (PMNs)
• Monocytes:
  • Less abundant than neutrophils (500-1000/mm3)
  • When traveled into tissues, called macrophages (monocytes/macrophage series)

Physical and Biochemical Defenses

• Exterior defense represented by physical and biochemical defenses
• Includes:
  • Lysozyme in most secretions
  • Sebaceous gland secretions
  • Mucus secretion
  • Spermine in semen
  • Acid in stomach
  • Potent biochemical substances (e.g. tears, lysozyme, complements)
  • Skin and mucus membrane
  • Cilia lining trachea
  • Commensal organisms in gut and vagina

Recognition of Microbes by Innate Immune System

• Recognizes structures that are shared by microbes, but not present on host cells
• Examples:
  • Phagocytes express receptors for bacterial LPS
  • Phagocytes express receptors for terminal mannose residues on bacterial glycoproteins
  • Phagocytes recognize and respond to ds RNA
  • Neutrophils and macrophages express receptors for antibodies and complement proteins

Immunology

• Study of immunity, cellular and molecular events that occur after exposure to microbes and other foreign macromolecules
• Immune system:
  • Defends against infections
  • Recognizes and responds to tissue grafts
  • Defends against tumor
  • Produces highly specific antibodies for detecting molecules
• Divided into:
  • Innate (Natural or Native) immunity
  • Adaptive (Acquired or Specific) immunity

Functions of Immune System

• Defense against infections
• Recognition and response to tissue grafts
• Defense against tumor
• Production of highly specific antibodies for detecting molecules

Immunology

• Immunology is the study of immunity, cellular, and molecular events that occur after exposure to microbes and other foreign macromolecules.
• It began as a study of the response of the whole animal to infection.
• Derived from the Latin word "Immunitas", which means a reaction of the immune system to foreign substances including microbes and macromolecules.

Immune System

• The immune system has various functions, including:
  • Defense against infections
  • Recognizing and responding to tissue grafts
  • Defense against tumors
  • Antibodies as highly specific reagents for detecting molecules
• The immune system is divided into two parts:
  • Innate (Natural or Native) immune system
  • Adaptive (Acquired or Specific) immune system

Innate Immune System

• The innate immune system is always present and ready to recognize and eliminate microbes.
• It is the first line of defense against infectious agents.
• Examples of innate immune system defense mechanisms include:
  • Physical barriers (e.g., skin, mucous membranes)
  • Phagocytic cells (e.g., neutrophils, monocytes, macrophages)
  • Eosinophils in the blood and tissues
  • Natural killer cells (NK)
  • Blood-borne molecules (e.g., lysozyme, acute phase proteins)

Adaptive Immune System

• The adaptive immune system is directed against microbial and non-microbial antigens.
• It produces specific reactions to each infectious agent, which normally eradicates the agent.
• It must be stimulated with microbes before it can be effective.
• It remembers the previous infectious agent and can prevent it (e.g., life-long immunity following infection).

Responses of Innate and Adaptive Immune Systems to Infection

• The innate immune system provides immediate defense against infection, while the adaptive immune system provides long-term protection.
• The innate immune system recognizes structures shared by microbes, whereas the adaptive immune system recognizes specific antigens.

Major Elements of Innate and Adaptive Immune Systems

• Innate immune system:
  • Soluble factors (e.g., lysozyme, complement, acute phase proteins)
  • Cells (e.g., phagocytes, natural killer cells)
  • Physiochemical barriers (e.g., skin, mucous membranes)
• Adaptive immune system:
  • Soluble factors (e.g., antibodies, lymphocyte-derived cytokines)
  • Cells (e.g., lymphocytes)
  • Physiochemical barriers (e.g., antibodies in mucosal secretions)

Recognition of Microbes by Innate Immune System

• The innate immune system recognizes structures shared by microbes, such as:
  • Lipopolysaccharides (LPS) on bacterial surfaces
  • Terminal mannose residues on bacterial glycoproteins
  • Double-stranded RNA (dsRNA) found in many viruses

Components of Innate Immunity

• Intact skin: provides a physical barrier against infection
• Phagocytes (e.g., neutrophils, monocytes, macrophages): recognize and ingest microbes for intracellular killing
• Natural killer cells (NK): recognize and kill infected cells or tumor cells
• Soluble factors (e.g., interferons, lysozyme, acute phase proteins): provide biochemical defenses against infection

Functions of Macrophages

• Produce cytokines that are important mediators of the host defense
• Secrete growth factors and enzymes that serve to remodel injured tissue and replace it with connective tissue
• Stimulate natural killer cells by secretion of IL-12
• Stimulate T lymphocytes and respond to products of T cells
• Engulf and digest foreign substances and microorganisms through phagocytosis

Immunology

• Immunology is the study of immunity, cellular, and molecular events that occur after exposure to microbes and other foreign macromolecules.
• It began as a study of the response of the whole animal to infection.
• Derived from the Latin word "Immunitas", which means a reaction of the immune system to foreign substances including microbes and macromolecules.

Immune System

• The immune system has various functions, including:
  • Defense against infections
  • Recognizing and responding to tissue grafts
  • Defense against tumors
  • Antibodies as highly specific reagents for detecting molecules
• The immune system is divided into two parts:
  • Innate (Natural or Native) immune system
  • Adaptive (Acquired or Specific) immune system

Innate Immune System

• The innate immune system is always present and ready to recognize and eliminate microbes.
• It is the first line of defense against infectious agents.
• Examples of innate immune system defense mechanisms include:
  • Physical barriers (e.g., skin, mucous membranes)
  • Phagocytic cells (e.g., neutrophils, monocytes, macrophages)
  • Eosinophils in the blood and tissues
  • Natural killer cells (NK)
  • Blood-borne molecules (e.g., lysozyme, acute phase proteins)

Adaptive Immune System

• The adaptive immune system is directed against microbial and non-microbial antigens.
• It produces specific reactions to each infectious agent, which normally eradicates the agent.
• It must be stimulated with microbes before it can be effective.
• It remembers the previous infectious agent and can prevent it (e.g., life-long immunity following infection).

Responses of Innate and Adaptive Immune Systems to Infection

• The innate immune system provides immediate defense against infection, while the adaptive immune system provides long-term protection.
• The innate immune system recognizes structures shared by microbes, whereas the adaptive immune system recognizes specific antigens.

Major Elements of Innate and Adaptive Immune Systems

• Innate immune system:
  • Soluble factors (e.g., lysozyme, complement, acute phase proteins)
  • Cells (e.g., phagocytes, natural killer cells)
  • Physiochemical barriers (e.g., skin, mucous membranes)
• Adaptive immune system:
  • Soluble factors (e.g., antibodies, lymphocyte-derived cytokines)
  • Cells (e.g., lymphocytes)
  • Physiochemical barriers (e.g., antibodies in mucosal secretions)

Recognition of Microbes by Innate Immune System

• The innate immune system recognizes structures shared by microbes, such as:
  • Lipopolysaccharides (LPS) on bacterial surfaces
  • Terminal mannose residues on bacterial glycoproteins
  • Double-stranded RNA (dsRNA) found in many viruses

Components of Innate Immunity

• Intact skin: provides a physical barrier against infection
• Phagocytes (e.g., neutrophils, monocytes, macrophages): recognize and ingest microbes for intracellular killing
• Natural killer cells (NK): recognize and kill infected cells or tumor cells
• Soluble factors (e.g., interferons, lysozyme, acute phase proteins): provide biochemical defenses against infection

Functions of Macrophages

• Produce cytokines that are important mediators of the host defense
• Secrete growth factors and enzymes that serve to remodel injured tissue and replace it with connective tissue
• Stimulate natural killer cells by secretion of IL-12
• Stimulate T lymphocytes and respond to products of T cells
• Engulf and digest foreign substances and microorganisms through phagocytosis