1) Humoral Immune System: Involves specific antibodies in the blood and lymph.
(The body's humors)
Produced by B cells.
2) Cellular Immune System: Involves T cells.That do not produce antibodies but secretecytokines.
Specialized lymphocytes respond to intracellular Ags
B cells mature in the bone marrow.
T cells mature in the thymus.
After maturation they migrate to lymphoid tissue.
Kinds of Immunity
Innate Immunity and Acquired Immunity
Acquired Immunity : Resistance to infection due to activity of antibodies.
a) Active Immunity
b) Passive Immunity
Naturally Acquired Active Immunity
1) Stimulus : Contact with a live microbe by natural processes. e.g. Infection; illness
2) Response : Symptoms of disease or subclinical RXN
Active production of specific antibodies to the
3) Duration : Long term (months - years),
sometimes life long.
Lots of exceptions: e.g. Influenza
Artificially Acquired Active Immunity
Antigen is intentionally introduced into the body.
1) Stimulus : Vaccines/Immunization:
a) Killed pathogens (or their proteins alone)
b) Attenuated/weakened live pathogens
c) Inactivated toxins (toxoids)
2) Response : Production of specific antibodies without developing symptoms of disease (or prodromal symptoms only)
3) Duration : Variable (Months-years-life time)
Passive Immunity: Immunity acquired through transfer of antibodies.
Naturally Acquired Passive Immunity
1) Mother to fetus through the placenta (placental transfer) or in colostrum/milk during nursing.
2) Response : No immune response. Acquisition of antibody only.
3) Duration : Short term (a few weeks -months)
Artificially Acquired Passive Immunity 1) Antibodies formed in one individualtransferred/injected into another individual.
Immune serum/gamma globulin
2) Response : No immune response, acquisition of antibody only.
3) Duration : Very short (2-3 weeks) e.g. Venomous snake bites, Tetanus, Hep. A, Diphtheria, Botulism.
ANTIGENS AND ANTIBODIES Specific immune response involves production of specific antibodies (Ab) against specific antigens (Ag).
The nature of antigens/Immunogens
1) Definition: An Immunogen is anysubstance that when introduced into the body stimulates the production of specific antibodies. An antigen is any substance that combines with those specific antibodies.
The term antigen is often used to mean both an antigen and an immunogen. 2) Characteristics : Foreign/Non-self matter
e.g. Microorganisms, toxins, foreign tissues.Chemically : Complex molecules: e.g. Protein or polysaccharide
Has reactivity (combines with specific antibodies) without immunogenicity (stimulating production of specific antibodies) unless bound to a carrier. Antigenic Determinant/Epitope
Antibodies are not formed against a whole organism but specific regions or chemical groups.
Nature of Antibodies/Immunoglobulins
•Definition: A protein produced by B lymphocytes in response to an immunogen/antigen and is capable of combing with that antigen.
•Gamma Globulins: From separation of blood proteins by electophoresis.
3) Antibody structure: Two heavy chains and two light chains.
Heavy and light chains both have a “C” or constant portion and a “V” or variable portion.
V Portion: is different for each kind of Ab and gives the Ab its specificity.
Ag binding occurs at the V portion.
C Portion: Constant for each class of Ab.
Fab: (Antigen binding fragment) The two “arms”
Fc: (Crystallizable fragment) The “trunk” of the antibody.
Contains the complement binding site.
Classes of Antibody
IgG: Monomer 80% of serum antibodies
(Most abundant Ab in serum) Can cross the placenta: protects fetus & newborn.