Questions and Answers
What is the role of the immune system?
Innate immunity is based on genetic make-up.
True
What are the two types of immunity mentioned?
Innate and Acquired
Match the following immune system components with their descriptions:
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Acquired immunity relies on mechanisms that adapt after ____.
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Which of the following are types of antibodies? (Select all that apply)
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IgG can cross the placenta.
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What is the major function of IgA?
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IgD is present on the surface of _ lymphocytes.
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Study Notes
Immunity and Immunology
- Immune system: cells, tissues, and molecules that mediate resistance to infections
- Immunology: study of structure and function of the immune system
- Immunity: resistance of a host to pathogens and their toxic effects
- Immune response: collective and coordinated response to the introduction of foreign substances in an individual mediated by the cells and molecules of the immune system
Role of the Immune System
- Defense against microbes
- Defense against the growth of tumor cells
- Homeostasis: destruction of abnormal or dead cells (e.g. dead red or white blood cells, antigen-antibody complex)
Immune System Components
- Organs: tonsils, adenoids, thymus, lymph nodes, spleen, Payer's patches, appendix, lymphatic vessels, bone marrow
- Cells: lymphocytes (T-lymphocytes, B-lymphocytes, plasma cells, natural killer lymphocytes), monocytes, macrophages, granulocytes (neutrophils, eosinophils, basophils)
- Molecules: antibodies, complement, cytokines, interleukins, interferons
Types of Immunity
- Innate (non-adaptive) immunity: first line of immune response, relies on mechanisms that exist before infection, rapid response, non-specific, no memory
- Acquired (adaptive) immunity: second line of response, relies on mechanisms that adapt after infection, handled by T- and B- lymphocytes, specific, has memory
Innate Immunity Mechanisms
- Mechanical barriers/surface secretion: skin, acidic pH in stomach, cilia
- Humoral mechanisms: lysozymes, basic proteins, complement, interferons
- Cellular defense mechanisms: natural killer cells, neutrophils, macrophages, mast cells, basophils, eosinophils
Adaptive Immunity
- Active and passive immunity
- Active immunity: natural (clinical or sub-clinical infection), artificial (vaccination: live, killed, purified antigen vaccine)
- Passive immunity: via breast milk, placenta, immune serum, immune cells
Adaptive Immunity Mechanisms
- Cell-mediated immune response (CMIR): T-lymphocytes eliminate intracellular microbes that survive within phagocytes or other infected cells
- Humoral immune response (HIR): B-lymphocytes mediate antibody production to eliminate extracellular microbes and their toxins
Cell-Mediated Immune Response
- T-cells recognize peptide antigen on macrophage in association with major histocompatibility complex (MHC) class, identifies molecules on cell surfaces, helps body distinguish self from non-self
- T-cells differentiate into effector cells that kill infected cells
T Lymphocytes
- Helper T-lymphocytes (CD4+): activate phagocytes to kill microbes
- Cytolytic T-lymphocytes (CD8+): destroy infected cells containing microbes or microbial proteins
Cell-Mediated Immune Response Phases
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Primary response: production of specific clones of effector T cells and memory clones, develops in several days, does not limit the infection
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Secondary response: more pronounced, faster, and more effective at limiting the infection
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Examples: cytotoxic reactions against intracellular parasites, delayed hypersensitivity (e.g., Tuberculin test), and allograft rejection### Immune Response
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Some B lymphocytes evolve into the resting state, known as memory cells.
Antibodies (Immunoglobulins)
- Belong to the gamma-globulin fraction of serum proteins
- Y-shaped or T-shaped polypeptides consisting of 2 identical heavy chains and 2 identical light chains
- Not all immunoglobulins are antibodies
- There are five kinds of antibodies: IgG, IgM, IgA, IgD, and IgE
IgG
- Accounts for 70-75% of total immunoglobulin
- Secreted in high quantities in secondary exposures
- Can cross the placenta
- Indicates active infection with a 4-fold rise or fall
- Major functions: neutralize microbes and toxins, opsonize antigens for phagocytosis, and activate the complement
- Protects the newborn
IgM
- Secreted initially during primary infection
- Cannot cross the placenta
- Presence in newborn indicates infection
- Major functions: activates the complement, used as a marker of recent infection
- Secreted first during primary exposure, used to detect early phase of infection
IgA
- Monomeric in serum, dimeric with secretory component in the lumen of the gastro-intestinal tract and in the respiratory tract
- Major function: neutralizes microbes and toxins
- Used in sero-diagnosis of tuberculosis and synactical respiratory virus tests
IgD
- Monomeric
- Major functions: present on the surface of B lymphocytes, functions as membrane receptor, and has a role in antigen-stimulated lymphocyte differentiation
IgE
- Mediates type I hypersensitivity
- Monomeric
- Major functions: associated with anaphylaxis, plays a role in immunity to helminthic parasites, and used in sero-diagnosis of infectious and non-infectious allergies
Sequential IgM-IgG Humoral Response
- IgM produced as a first response to many antigens, levels remain high transiently
- IgG produced after IgM, higher levels persist in small amounts throughout life, produced in large amounts during secondary response
- Persistence of antigen-sensitive ‘memory cells’ after primary response
Failure of Immune Response
- Immune response helps individuals defend against microbes and some cancers
- Immune response can fail, resulting in hypersensitivity reactions, immunodeficiency, and others
Hypersensitivity Reactions
- Cause cell damage through excessive immune response to antigens
- Types: hypersensitivity, allergy, and autoimmunity
Immunodeficiency
- Loss or inadequate function of various components of the immune system
- Can occur in any part or state of the immune system
- The immuno-compromised host has an impaired function of immune system and is at high risk of infection
Types of Immunodeficiency
- Congenital (primary) immunodeficiency: genetic abnormality, defect in lymphocyte maturation
- Acquired (secondary) immunodeficiency: results from infections, nutritional deficiencies, or treatments, such as AIDS or chronic leukemia
Altered Immunity: Immuno-compromised
- Altered anatomic barrier: reduction in IgA, elevated pH, and change in flora
- Immune system disorders: reduction of complement, neutropenia, monocytopenia, reduction of T cells, and hypo-gammaglobulinemia
Summary (1)
- Innate immunity relies on mechanisms already existing before microbe infects host
- Is the first line of defense
- Has no memory for subsequent exposure
- Relies on non-specific mechanisms
Summary (2)
- Adaptive immunity develops following entry of microbe into the host
- Comes into action after innate immunity fails to get rid of microbe
- Has memory to deal with subsequent exposure
- Happens through specific cells: T cells (cell-mediated) and B cells (antibody-mediated)
Summary (3)
- Primary immune response: short-lasting, smaller in magnitude
- Secondary immune response: longer in duration, larger in magnitude, develops ‘memory cells’ following primary response
- Failure of immune response can result in hypersensitivity, immunodeficiency, and others
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Description
Learn about the immune system, immunology, and immunity, including cells, tissues, and molecules that mediate resistance to infections and the collective response to foreign substances.