Adaptive Immunity

• Develops after exposure to specific antigen
• The adaptive immune response has memory
• Works together with inflammation
• Provides long-term protection
• Is slower than innate but more specific
• Recognizes foreign or “nonself” substances
• Antigens
  • Pathogens: bacteria, fungi, viruses, parasites
    Noninfectious environmental agents: pollen, foods, bee venom
    Drugs
    Vaccines
    Transfusions
    Transplants

inducible (able to be caused), specific, and long-lived, and by having memory

third line of defense in the human body is adaptive (acquired)
immunity, often called the immune response or immunity, and
consists of lymphocytes

Adaptive Immunity: T and B Cells

• End products of adaptive immunity
  • Lymphocytes: T and B cells
    Antibodies: Immunoglobulins (Ig)
• Primary lymphoid organs: Is the thymus for T cells and bone marrow for B cells
• It is estimated that each person has produced a population of B and T cells
  with an extensive diversity of antigen receptors capable of recognizing
  at least 108 different antigens. This process is called generation of
  clonal diversity
• Each individual T or B cell specifically recognizes only one particular antigen
• Both B and T cells also develop cell surface antigen receptors
• B cells develop into plasma cells that become factories for the production of antibody.
• T cells develop into several subsets
  • identify and kill a target cell T-cytotoxic cell [Tc cell
  • regulate the immune response by helping the clonal selection process- T-helper cell [Th cell
  • suppress or limit the immune response T-regulatory cell [Treg cell]).

Adaptive Immunity: Humoral and Cellular immunity

Humoral immunity

• B cells and circulating antibodies are the primary cells
  • Antibody is primarily responsible for protection
    against many bacteria and viruses.
• Causes direct inactivation of a microorganism or the activation of inflammatory mediators

Cellular immunity

• Differentiates T cells
• Primarily protects against viruses and cancer
  • identify and kill a target cell T-cytotoxic cell (Tc cell)
  • regulate the immune response by helping the clonal selection process- T-helper cell (Th cell)
  • suppress or limit the immune response T-regulatory cell (Treg cell).
• Effector T cells are found in the blood and in tissues and organs and
  defend against intracellular pathogens (e.g., some viruses) and cancer
  cells.
• Humoral and cellular immunity work together to provide immunity and memory.
• Respond more rapidly and efficiently on subsequent exposure to the same antigen.

Adaptive Immunity: Active vs. Passive Immunity

Active

• produced by an individual either after
  natural exposure to an antigen or after immunization
• active acquired immunity is long lived

Passive

• passive immunity occurs when preformed antibodies or T lymphocytes are transferred from a donor to the recipient
• occurs naturally or artificially
  • maternal antibodies across the placenta to the fetus
  • artificially, as in a clinic using immunotherapy for a specific disease
• Is temporary or short-lived.

What is an Antigen?

• Is a molecule that can react with antibodies or receptors on B and T cells
• Is mostly protein but can be other molecules as well
• Antigen is a commonly used term to describe a molecule that can react with binding sites on antibodies or antigen receptors on B and T cells
• not all, antigens are also immunogens
• An antigen that is immunogenic will induce an immune response, resulting in the production of antibodies or functional T cells

What is an Antibody?

immunoglobulin, is a serum glycoprotein produced by plasma cells in response to a challenge by an immunogen

• Is also called immunoglobulin (Ig)
• Is produced by plasma cells
• Has several classes
• IgG, IgA, IgM, IgE
• Are characterized by antigenic, structural, and functional differences

IgG

How can it be aquired?

Most protective activity against __?

• IgG
• Is the most abundant class (80% to 85%)
• Is transported across the placenta
  • Maternal IgG is transported across the placenta during pregnancy and protects the newborn child during the first 6 months of life
• Accounts for most of the protective activity against infections

IgA

Where is it mostly found?

• IgA mostly in secretions
• Has two subclasses
• IgA1 molecules: Are predominantly in the blood.
• IgA2 molecules: Are predominantly in normal body secretions.

IgA dimer inside mucosal epithelial cells and protects these immunoglobulins against degradation by enzymes also found in the secretions

IgM

Characteristics?

When does it respond?

IgM

• Is the largest of the immunoglobulins

• Is the first antibody produced during a response to an antigen

IgE

When does IgE act?
Concentration?

• IgE “echuu” & “ParEEEsite”
• Most Rare
• Acts as a mediator of many common allergic responses “eechu”
• Defends against parasites
• found in low concentrations in the circulation

IgD

Not well known

• Functions as one type of B-cell antigen receptor.

B-Cell Maturation

• Occurs in the bone marrow
• Stem cell matures

Stem cells in the bone marrow or fetal liver.

Lymphoid stem cells are precursor cells formed in the liver (in the fetus) or in the bone marrow (of a child or
adult)

Lymphoid stem cells destined to become B cells percolate through
specialized regions of the bone marrow, where they are exposed to
hormones and cytokines that induce proliferation and differentiation
into immunocompetent B cells

T-Cell Maturation

• Thymus is the central lymphoid organ of T-cell development
• T cells move from the thymic cortex to the medulla
  • they are instructed by interactions with various thymic cells (epithelial cells, macrophages, and dendritic cells), thymic hormones (e.g., thymosin, thymopoietin, thymostimulin, and others produced by the thymic epithelium), and the cytokine IL-7 to undergo proliferation and
    progressive development of the characteristics of immunocompetent
    T cells
• T cells are released into the blood and take up residence in the secondary lymph organs to await antigens.

What are some Secondary Lymphoid Organs

Include: “ T PALS”

• spleen
• lymph nodes
• adenoids
• tonsils
• Peyer patches (intestines)
• appendix

Immunocompetent lymphocytes are released to the circulation and many reside in secondary (peripheral) lymphoid organs (e.g., spleen, lymph nodes, adenoids, tonsils, Peyer patches).

After maturation in the central lymphoid organs, these stem cells develop
into immunocompetent cells with antigen-specific receptors without
encountering foreign antigen.

Primary Response

• Primary immune response
• Occurs during the initial exposure
• After 5–7 days, an IgM antibody for a specific antigen is detected
• An IgG response equal to or slightly less follows the IgM response
• The immune system is primed

there is a latent period, or lag phase.

After approximately 5 to 7 days, IgM antibody specific for that antigen can be detected in the circulation followed by the production of IgG against the same antigen

amount of antibody in a serum sample is frequently referred to as the titer

lag phase is a result of the time necessary for clonal selection, including processing and presentation of antigens, induction of Th cells, interactions between
immunocompetent B cells and Th cells, and maturation and proliferation of the B cells into plasma cells and memory cells

Secondary response

• Is more rapid than the primary response.
• Larger amounts of antibody are produced.
• IgM is produced in similar quantities to the primary response, but IgG is produced in considerably greater numbers.

rapidity of the secondary immune response is the result of the presence of memory cells that require little further differentiation into plasma cells

Fetal and Neonatal Immune Function

• Newborns have a poorly developed immune response.
• Antibody function of the newborn is deficient.
• Is capable of primary IgM response, but is unable to produce an IgG challenge.
• Immunity is provided by maternal antibodies

Aging and Immune Function

• Decreased T-cell activity
• Thymic size is 15% of its maximum size
• Decreased production of specific antibodies
• Decreased circulating memory B cells
• Increased circulating immune complexes
• Increased circulating autoantibodies

Antigen

• Is an exaggerated response against an environmental antigen

Autoimmunity

• Is a misdirected response against the host’s own cells
• disturbance in the immunologic tolerance of self-antigens

Alloimmunity

• Iimmune response directed against beneficial foreign tissues, such as transfusions or transplants

Immune deficiency

• Immune response is insufficient to protect the host

Hypersensitivity

Is an altered immunologic response to an antigen that results in disease or damage to the host.

Sensitization

Adequate amount of antibodies or T cells is available to cause noticeable reaction on re-exposure to antigen

Hypersensitivity reactions require sensitization against a particular
antigen that results in primary and secondary immune responses

Usually a sensitization process involving multiple exposures to the
allergen occurs before adequate amounts of antibody or T cells are
available to elicit a hypersensitivity response

Immediate hypersensitivity reaction

• Reaction that occurs within minutes to a few hours
• Anaphylaxis: systemic or cutaneous

Delayed hypersensitivity reaction

• Reaction that takes several hours to appear
• Maximum severity occurs days after re-exposure to the antigen

Anaphyslaxis

most rapid and severe immediate hypersensitivity reaction

occurs within minutes of re-exposure to the antigen

can be either systemic (generalized) or cutaneous (localized)

• Severity depends on the level of sensitization
• Systemic anaphylaxis include itching, erythema, headaches, vomiting, abdominal cramps, diarrhea, and breathing difficulties
  • most severe reactions may include contraction of bronchial smooth muscle, laryngeal edema, and vascular collapse and decreased blood pressure that can lead to shock and death
  • EX of systemic reactions: Bee stings, peanuts, eggs, and shellfish, among others, can cause anaphylaxis
• Cutaneous anaphylaxis results in local symptoms, such as pain, swelling, and redness, which occur at the site of exposure to an antigen

Type I Hypersensitivity

• Is immunoglobulin E (IgE) mediated
• Is against environmental antigens (allergens)
• IgE binds to mast cells; causes the release of histamine from mast cell degranulation

H1 and H2 receptors

• Manifestations
  from H1
• Bronchial constriction
• Edema
• Vasodilation

• Manifestations
  from H2
• Increases gastric secretions
• Decreases the release of histamine from mast cells and basophils

Tx with Benadryl or Zantac

Type II Hypersensitivity

• Tissue specific
• Specific cell or tissue (tissue-specific antigens) is the target of an immune response
• Examples
• Graves disease
• Hemolytic transfusion reactions
• Rh incompatibility
• Drug induced hemolytic anemia

Type III Hypersensitivity

• Is immune (antigen-antibody) complex mediated
• Complexes are formed in the circulation and deposited later in vessel walls or extravascular tissues
• Is not organ specific
• Examples
• Lupus, Rheumatoid Arthritis, Raynaud's serum sickness, post-streptococcal glomerulonephritis

Type IV Hypersensitivity

• Is mediated by T lymphocytes or is cell mediated
• Examples
• Acute graft rejection, skin test for tuberculosis (TB), contact allergic reactions, and some autoimmune diseases