Immunology Basics Quiz

Introduction to Immunology

• Immunology is the study of the immune system
• Humans are constantly exposed to microorganisms.
• Colonization of body surfaces by microorganisms is common.
• Damage to the host by microorganisms is rare.
• Host defense mechanisms restrict invasion by normal flora, potential pathogens, and non-indigenous microorganisms.
• Colonization can be tolerated by hosts but restricted to areas where it does no harm
• Infection occurs when a parasite breaches an anatomical barrier or progresses beyond colonization.
• Pathological harm to the host resulting from infection is termed an infectious disease
• The immune system is responsible for host defense mechanisms

Host Defense Mechanisms

• The immune system has two major subdivisions, innate and adaptive
• Innate immunity is the primary defense against invading pathogens
• Adaptive immunity is the immune system's second line of defense
• Innate and adaptive systems work together
• Cells and components of the innate system influence the adaptive system, vice-versa.

Innate Immunity

• Innate immunity is a non-specific defense mechanism.
• Innate mechanisms are constitutive to the host.
• Constitutive means they are continually ready to respond to invading microorganisms without needing time for induction.
• Components of innate immunity include anatomical barriers; normal flora; tissue bactericides; complement components; ability to induce an inflammatory response; and phagocytic response.
• Innate immunity provides the first line of defense against invading bacteria

Anatomical Barriers

• Skin
  • Intact epidermis is rarely penetrated
  • Microbes may enter broken or damaged skin
  • Normal flora produces substances discouraging colonization (e.g., fatty acids)
  • Perspiration contains lysozyme
• Mucous Membranes
  • Colonized by bacteria
  • Limited entry of pathogens
  • Contain antimicrobial compounds

Adaptive Immunity Characteristics

• Adaptive immunity is specific in its reaction to a pathogen and reacts accordingly
• Adaptive immunity has immunological memory
• This "remembering" allows for a quicker response upon re-exposure
• Innate immunity does not have memory

Cellular Defense

• Various tissue cells are involved in innate and adaptive immunity
• Cells involved in phagocytosis include neutrophils and macrophages.
• Basophils and mast cells are involved in inflammation
• B cells and T cells are key for antibody mediated and cell mediated immunity, respectively.
• All these cells originate in the bone marrow

Cells of Immune System

• Myeloid progenitor cells differentiate into neutrophils, eosinophils, basophils, monocytes, and dendritic cells.
• Lymphoid progenitor cells differentiate into T cells and B cells.
• Macrophages and dendritic cells play roles in innate and adaptive immunity.
• Other factors involved in cell-mediated immunity, and antibody-mediated immunity.

Therapy Against Other Diseases

• Treating other diseases may make a person more susceptible to infection
• Diseases and conditions that suppress the immune response decrease the body's ability to fight infection

Complement

• Complement is part of the innate immune system
• It plays a crucial role in inflammation, phagocytosis, and bacterial killing
• It can be activated by bacterial invasion, antigen-antibody reactions, and other means
• Complement is an enzymatic system of serum proteins (C1-C9)
• It has classical and alternative pathways leading to a variety of antibacterial defenses
• The various components of complement work together for phagocytic chemotaxis, opsonization, and inflammatory responses and can result in the lysis of certain bacteria, viruses, and other microorganisms

Phagocytic Defenses

• Recruitment of phagocytes occurs in response to inflammation
• Phagocytes (cells capable of ingestion) are responsible for the destruction of microorganisms that cause inflammation
• First to accumulate are neutrophils
• Local and blood-borne macrophages subsequently migrate to the site of infection and initiate phagocytosis

Properties of Neutrophils

• Neutrophils originate in multi-potential stem cells in the bone marrow
• They have a short lifespan (2-3 days)
• They make up 30-70% of circulating white blood cells
• They are phagocytic and actively participate in inflammation, killing microorganisms through various mechanisms
• They differentiate and mature in the bone marrow, where division ceases and mitochondria and endoplasmic reticulum disappear
• They're motile and actively phagocytic
• Only about half of circulating neutrophils are detectable in the blood at a given time

Properties of Macrophages

• Macrophages, also known as mononuclear phagocytes
• Originate from monocytes in the bone marrow
• They circulate in the bloodstream for about 1-3 days before migrating to tissues, where they mature into macrophages
• Monocytes mature to macrophages to become phagocytic, more active and more granules.

The Phagocytic Process

• Phagocytosis involves sequential steps including delivery of phagocytes to the site of infection, adherence to the target, ingestion, phagolysosome formation, intracellular killing, and digestion.

Inflammation

• Inflammation is vital for all host defenses
• It focuses various circulating antimicrobial components to a site of infection
• Inflammation is a tissue reaction in response to infection or injury characterized by redness, swelling, heat, and pain
• Phagocytes, lymphocytes, and components of plasma are part of the inflammatory response
• Inflammation is both helpful and detrimental in that it can be induced by immunological reactions, tissue damage, and certain pathogenic agents but also has the potential to damage the host by inducing excessive responses

Innate Vs Adaptive Immunity

• Innate immunity is non-specific and fast; adaptive immunity is specific and slow
• Innate immunity has no memory
• Adaptive immunity exhibits memory
• Adaptive immunity acts to prevent disease. Innate immunity, by itself, may not be

Antigens

• Antigens are foreign substances (not part of the animal's tissues)
• They have a molecular weight greater than 12,000 daltons
• They trigger a specific immunological response

Active Vs Passive Immunity

• Adaptive immunity can be acquired through active or passive means