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The Final Line of Defense
Adaptive or Specific Immunity
Features of Adaptive Immunity:
Antigen specificity - selectively recognizes and acts against particular foreign substances (i.e. immunity to one disease does not necessarily cause immunity to another).
Acquired - because it develops during a person’s lifetime on exposure to specific harmful agents.
Systemic - not restricted to the initial infection site.
Memory - recognizes and mounts a stronger attack on previously encountered pathogens.
Adaptive Body Defenses
•Immune response - is the Immune system’s response to a threat such as microorganisms, pollen, drugs, poison ivy, animal dander, detergents etc.(most of them are proteins)
•Initial exposure - primes the body
•Antigens - are molecules which elicit an immune response or bind to components of the immune system, such as antibodies.
•Self-antigens:
Human cells have many surface proteins.
Our immune cells do not attack our own proteins.
MHC-Major histocompatibility Complex (serves as a barcode)
In an Autoimmune disease, body fights against its own cells.
•Haptens - are small molecules which are antigenic in nature, but cannot elicit an immune response; this means that a hapten can only react with a specific antibody but cannot trigger an immune response. Hapten is essentially an incomplete antigen.
Cells of the Adaptive Defense system
Lymphocytes:
•Both T and B lymphocytes develop from hemocytoblasts (stem cells) in the red bone marrow, as do all blood cells.
•T Lymphocytes- migrate to thymus and become T cells (this constitutes about 80% of lymphocytes in blood).They undergo maturation in the Thymus directed by the hormone Thymosin.
•B Lymphocytes- develop immunocompetence in the bone marrow itself.
•Antigen Presenting Cells (APCs): mediate the cellular immune response by processing and presenting antigens for recognition by certain lymphocytes such as T cells.
APCs
Dendritic cells
Macrophage
B Lymphocytes
Adaptive Immunity - Classification
There are two major types of Adaptive Immunity:
Humoral Immunity – “B” Cell mediated
Cell Mediated Immunity – “T” cell mediated
Adaptive Defense
Humoral Immunity - B Cell mediated
The B lymphocytes (B cells) mature in the red bone marrow before becoming active in the blood.
B cells have surface receptors that bind with a specific type of antigen.
This binding sensitizes, the lymphocytes to Clonal Selection.
B cells rapidly multiply into large numbers of plasma cells.
The plasma cells produce antibodies or immunoglobulins (Igs) against the original antigen, and release them into the blood, providing a form of immunity described as humoral immunity.
Primary Response - 4-5 days; Antibody peak in 10 days.
Those B cells that do not become plasma cells become the Memory cells for future attack by the same antigen.
Secondary Response – within hours; antibody peaks in 2-3 days.
Adaptive Immunity:
Antibodies / Immunoglobulins
All antibodies are contained in a portion of the blood plasma called gamma globulin fraction.
The antibody can bind only to the antigen that caused its production.
Antibodies do not destroy cells directly; rather, they assist in the immune response.
Some of the activated B cells do not become plasma cells but, like certain T cells, become memory cells.
Classes of Antibodies
There are five different classes of antibodies (“GAMED”)
IgG (75%)—found in blood, lymph, and intestines, can cross the placental barrier and confer immunity from mother to fetus;
IgA (15%)—found mainly in exocrine gland secretions, nasal fluid, tears, gastric and intestinal juice, bile, breast milk and urine
IgM (5%-10%)—found in blood and lymph; first antibody produced in an immune response.
IgE (<0.1%)—located on basophils and mast cells- active in allergic reactions and parasitic infections.
IgD (< 1%)—located on surface of B cells.
Functions of the Antibodies
Complement fixation – there are 20 inactive complements that get activated
Neutralization – when they bind to specific sites and block the harmful effects of the virus / exotoxin.
Agglutination – process causing clumping of the foreign cells.
Precipitation – as a result of the cross linking process the antigens become large, insoluble and settle out as precipitates.
Naturally Acquired Immunity
Naturally Acquired Active Immunity:
Occurs naturally through contact with a specific pathogen or its toxins.
Ex: suffering the disease like Measles.
May last for years, and in some cases for life.
Because the host is actively involved in generating protection, this type is described as active immunity.
Because the immunity is formed against harmful agents encountered in the normal course of life, it is called natural active immunity.
Natural Passive Immunity
Naturally Acquired Passive Immunity:
Occurs when antibodies are obtained from someone else.
Conferred naturally from a mother to her fetus (naturally acquired) through placenta.
Conferred naturally from receiving gamma globulin, via breast milk.
These donated antibodies provide immediate protection, but only lasts 2-3 weeks.
Immunological memory does not occur.
Artificially Acquired Immunity
A person unexposed to a particular antigen has no antibodies or T cells against that pathogen, and may be defenseless against that infection.
Hence artificial measures may be used to establish immunity.
Artificially acquired immunity may be
Artificially Aquired Active Immunity:
Vaccination: Artificial acquired active immunity is
through vaccinations against particular pathogens.
Artificially Aquired Passive Immunity:
Immune Sera: Artificial acquired passive immunity is
through injection of immune globulins (gamma globulins)
after presumed exposure to a particular pathogen.
Ex: Anti Tetanus Serum
Adaptive Immunity:
Cell Mediated Immunity - T cell Mediated
There are several types of T cells, each with different function:
Helper T cells:
Release substances such as Cytokines.
Cytokines stimulate the production of more cytotoxic T cells, B cells and macrophages.
Note: The Corona Virus is causing a Cytokine storm to hit the body’s immune system.
Cytotoxic or Killer T cells: (Phagocytosis)
Recognize cells infected with viruses or other intracellular pathogens, cancer cells, and foreign antigens present on transplanted tissue.
Binding to a foreign cell, releases toxins called Perforins which form pores in the plasma membrane of these cells, allowing Granzymes to enter and destroy them.
Suppressor T cells:
Halts the immune response in order to prevent over-activity of the T and B cells.
Memory T cells:
Left behind in the system to remember the antigen and start
a rapid response if that antigen is encountered again.
These thymus-derived lymphocytes produce an immunity that is called the cell-mediated immunity.
The T cell population is generally responsible for defense against -
cancer cells
certain intracellular viruses
the rejection of tissues transplanted from another person.
Disorders of Immunity
Autoimmune Diseases:
Body reacts to its own tissues.
- Rheumatoid Arthritis
- Myasthenia Gravis
- Multiple Sclerosis
- Grave’s Disease
- Type I Diabetes Mellitus
- Systemic Lupus Erythematosus
- Glomerulonephritis
Allergies and Anaphylaxis:
(Anaphylaxis – is the life threatening form of severe allergy)
*AIDS: opportunistic infections