Immunology - Classifications - Cells Involved - Immunoglobulins

2.  Term immune derived from Latin word immunis means exempt
from charges.
 Concept of immunity introduced by Thucydides in 430 BC about
plague i.e. only recovered people nurse the sick one.
 In 1798, Edward Jenner introduced vaccination against smallpox by
means of using cowpox
 Immunology deals with the study of immunity and immune system
of vertebrates.
 The ‘science of immunology’ categorically deals with the specific
mechanisms by which the living tissues invariably react to the so
called foreign biological materials, such as : invading pathogenic
microorganisms, so that ultimately either immunity or resistance
gets developed in vivo to combat the dreadful diseases in the
humans and animals.

3.  An antigen is either a cell or molecule which will bind with
preexiting antibody but will not definitely cause induction of
antibody production.
 Antigen may also be defined as — ‘a macromolecular entity that
essentially elicits an immune response via the formation of specific
antibodies in the body of the host’.
 Generally, immunogens (antigens) must fulfil the following two
cardinal characteristic features, namely :
› Should be larger than 2000 in molecular weight, e.g., protein,
glycoprotein and carbohydrates,
› Must be absolutely foreign to the individual into whom they
have been introduced appropriately.
 Hapten may also be defined—‘as a substance that normally does
not act as an antigen or stimulate an immune response but that
can be combined with an antigen and, at a later time, initiate a
specific antibody response on its own’.

4. IMMUNITY
Innate (non-
specific)
Adaptive
(Specific)
Natural Acquired
Active
Naturally
Acquired
Following
Clinical
Infections
Artificially
Acquired
Following
administration
of vaccines
Passive
Naturally
Acquired
Mother to
Fetus
Artificially
Acquired
Following
administration
of Antiserum

5.  INNATE IMMUNITY:
› Non-specific, defensive barrier.
› First line of defense: Skin provides mechanical barrier against
microorganisms and viruses. Acidic (pH 3-5) environment and
sweat’s enzyme Lysozyme on skin surface inhibit microbial
growth.
› Second line of defense: Sneezing and secretion of mucus,
phagocytosis by macrophages and complement system,
inflammatory and fever response.
 ADAPTIVE IMMUNITY:
› Specific, recognizing and eliminating the invading antigen
› Characterstics:
 Antigen specificity
 Recognition diversity
 Immmunological memory
 Discrimination between self and non-self

6. › Natural Immunity: resistance by individual, Negroes are
resistant to yellow fever while whites are susceptible
› Acquired Immunity: Developed during lifetime, non inherent,
introduction or production of antibody against antigen
› Active Acquired Immunity: Developed slowly and long lasting,
prevent disease and administered before infection, antigen are
administered.
› Passive Acquired Immunity: Produced fast and short lived,
administered after infection, antibodies are administered
 Organization of immune system:
› Primary Organ: provide microenvironment for development
and maturation of lymphocyte. i.e. :- Thymus and Bone Marrow
› Secondary Organ: provide microenvironment for antigen and
lymphocyte interaction. i.e. :- Spleen, lymph nodes, tonsils,
appendix, etc.

8.  Cell of Immune System:
› B-Lymphocytes: development and maturation occur in bone
marrow in mammals. They mature into plasma cells and
secrete immmunoglobulins. They are associated with humoral
immunity. After encounter with antigen they divide rapidly into
memory B cell and plasma cells.

9. › T-Lymphocytes: maturation occur in thymus. They have distinct
antigen binding site. Protein present on surface i.e. Major
Histocompatibility complex (MHC) is responsible for antigen
recognition. Four types:-
 Inducer T-cells: mediate development of t cells
 Cytotoxic T-cell (TC): recognizing and killing infected or abnormal
cells
 Helper T-cell (TH): initiate immune response
 Suppressor T-cell: suppression of immune response

10.  Macrophages develop from monocytes,
a type of white blood cell. Macrophages
have an irregular shape with short
branching projections and are capable
of engulfing bacteria and cellular debris
by phagocytosis. Fixed macrophages
reside in a particular tissue; examples include alveolar
macrophages in the lungs or splenic macrophages in the spleen.
Wandering macrophages have the ability to move throughout the
tissue and gather at sites of infection or inflammation to carry on
phagocytosis.
 Natural killer cells are a part of the lymphoid linage of white
blood cells. They are large granular lymphocytes that represent 10-
15% of circulating lymphocytes in the blood. Cytokines secreted
from macrophages activate and facilitate the entry of NK cells into
tissue to reduce proliferation.

11.  Antibodies are a group of glycoproteins present in serum or tissue fluids
of all animals.
 They are present on B-cell membrane and secreted by plasma cells
 They circulate in the blood, searching for neutralizing or eliminating
antigens.
 Structure:
› Contain two identical heavy chains
(mol wt. 53,000 to 75,000 each &
approx. 450 amino acids) and two
identical light chains (mol wt. 23,000
each & 212 amino acids) held together
by disulfide linkage and non covalent
interactions. Heavy chain is linked to
carbohydrate.
Each chain has constant and variable
regions or domain variable region are
responsible for antigen specificity.

13.  Cytokines: group of proteins that bring communication between
different cell types involved in immunity. They are soluble
messenger molecules. They may be short range or long range.
They amplify immune and inflammatory response. IL-2 is used in
cancer immunotherapy and in immunodeficiency disease.
 IMMUNITY AND HEALTH AND DISEASE:
 The prime function of immune system is to protect the host
against the invading pathogens. The body tries its best to
overcome various strategies of infectious agents (bacteria, viruses)
and provide immunity. But sometimes, for various reasons, the
immune system fails to discriminate between self and non self. As
a consequence, the cells or tissues of the body are attacked. This
phenomenon is referred as autoimmunity and diseases regarded
as autoimmune disease.
 Insulin dependent diabetes, Rheumatoid arthritis, Myasthenia
gravis, Autoimmune hemolytic anemia.

14.  ORGAN TRANSPLANTATION: The phenomenon of transfer of cells,
tissues or organs from one site to another (in the same organism,
autograft or from another organism allograft) is regarded as organ
transplantation. Organ transplantation is associated with
immunological complications, and tissue rejection. This is because
the host body responds to the transplanted tissue in a similar way
as if it were an invading foreign organism.
 CANCER: Growth of tumors is often associated with the formation
of novel antigens. These tumor antigens (also referred to as
oncofetal antigens e.g. -fetoprotein) are recognized as non-self by
the immune systems. However, tumors have developed several
mechanisms to evade immune responses.
 AIDS: Acquired immunodeficiency syndrome (AIDS), caused by
human immunodeficiency virus, is characterized by
immunosuppression, secondary neoplasma and neurological
manifestations. AIDS primarily affects the cellmediated immune
system which protects the body from intracellular parasites such as
viruses, and bacteria.