INTRODUCTION
Immunity
especially an infectious disease’.
Importantly, this particular state is invariably induced by having been exposed to the
antigenic
marker
on an microorganism that critically invades the body or by having been duly immunized with a
vaccine
capable of stimulating the production of specific antibodies.
Immunology,
the generation of an immune response solely depends upon the prevailing
interaction of
three cardinal components of the immune mechanism, such as :
immunogen stimulation,
humoral immune system, and
cellular immune system.
Since 1901 and as to date the epoch making discovery and spectacular evolution of
‘immunobiotechnology’
i.e., conglomeration of immune system variants, across the world has
revolutionized not only the safer quality of life of human beings but also provided a broad spectrum of
newer avenues in combating the complicated dreadful not-so-easy diseases of the present day.
Immune Response :
In reality, the immune responses do refer to such processes whereby animals
(including humans) give rise to certain
specifically reactive proteins (known as ‘antibodies’) and
adequate cells in response to a great number of
foreign organic molecule and macromolecule variants.
Based on the scientifically demonstrated proofs and evidences the generalized
immune response
essentially possesses
four major primary characteristic features, such as :
(
a) discrimination,
(
b) specificity,
(
c) anamnesis, and(d) transferability by living cells.
Discrimination
It usually designates the
‘ability of the immune system’ to have a clear-cut discrimination
between
‘self’ and ‘nonself’ ; and, therefore, it invariably responds exclusively to such materials that
happen to be
foreign to the host.
Specificity
It refers to such a response that is extremely specific either solely for the
inducing material or
antigen
to which the immune cells or antibodies would interact in a much prominent and greater
strength.
Anamnesis
It most commonly refers to the critical ability to elicit a larger specific response much more
rapidly on being induced by a
‘second exposure’ to the same very foreign antigen. It is also termed as
the
anamnestic response or the immunologic memory, as illustrated in Fig. 9.1.
Transferability by Living Cells
Interestingly, the
active immunity is observed to be exclusively transferable from one particular
inbred animal specimen to another by the respective
‘immune cells’ or ‘lymphocytes’, and definitelynot by immune serum*
Adjuvants :
It has been duly observed that there exist quite a few nonspecific substances,
namely :
alum, mineral oil, that essentially do possess the abiliy to prolong as well as intensify the
ensuing
immune response to a particular antigen on being injected simultaneously with the antigen.
In fact, such materials are termed as
adjuvants by virtue of the fact that they profusely aid the immuneresponse.
In other words,
acquired immunity invariably refers to the ‘protection’ an animal inherently
develops against certain types of microorganisms or foreign substances. In reality, the
acquired immunity
gets developed in the course of an
individual’s lifespan. Fig. 9.2 depicts the different types of
acquired immunity in a summarized form.
Active Immunity
Active immunity
refers to the specific immunity obtained from the development within the body
of
antibodies or sensitized T lymphocytes (T Cells) which critically neutralize or destroy the infective
agent. It may eventually result from the
immune response to an invading organism or from inoculation
with a vaccine essentially containing a
foreign antigen.
Cell-Mediated Immunity [or T-cell Mediated Immunity]
It has been duly observed that the
regulatory and cytotoxic actions of T cells during the specific
immune response
is known as the cell-mediated immunity. However, the entire process essentially
needs almost 36 hr to accomplish its full effect. It is also called as
T cell mediated immunity.
Physiological Actions :
Interestingly, unlike B cells, T cells invariably fail to recognize the so
called
foreign antigens on their own. A foreign antigen is duly recognized by a macrophage which
engulfs it and displays part of the antigen on its surface next to a
histocompatibility or ‘self’ antigen
(macrophage processing). Finally, the presence of these two markers together with the secretion of a
cytokine, interleukin-1 (IL-1)
by macrophages and other antigen-presenting cells duly activates CD4+/
CD8 T cells (
i.e., helper T cells), that categorically modulate the activities of other cells adequately
involved in the
immune response.
Thus, the
CD4+T cells secrete interleukin-2 (IL-2), that stimulates the activity of natural killer
cells (NK cells), cytotoxic T cells,
and B cells ; and ultimately promotes the proliferation of CD+T cells
in order that the invading pathogen may be destroyed or neutralized effectively. Besides,
Gamma
Interferon
secreted by CD+T cells increases distinctly the macrophage cytotoxicity and antigen
processing.
However, the T-cell mediated immunity plays a significant and pivotal role in the rejection
of transplanted tissues
and in ‘tests for allergens’ i.e., the delayed hypersensitivity reaction.
Congenital Immunity
The
congenital immunity refers to the immunity critically present at birth. It may be either
natural or acquired, the latter predominantly depends upon the antibodies solely received from the mother’s
blood.
Herd Immunity
The
herd immunity represents the immune protection duly accomplished via vaccination of a
portion of a population, that may eventually minimise the spread of a disease by restricting the number
of potential hosts for the respective pathogen.
Humoral Immunity [or B-cell Mediated Immunity]
Humoral immunity
respresents the immunity duly mediated by antibodies in body fluids e.g.,plasma or lymph. As these antibodies are adequately synthesized and subsequently secreted by B cells,
that protect the body against the
infection or the reinfection by common organisms, such as : streptococci
and
staphylococci, it is also known as B-cell mediated immunity. In reality, the B cells are stimulated
by direct contact with a foreign antigen and differentiate into the
plasma cells that yield antibodies
against the antigen ; and the corresponding
memory cells which enable the body to rapidly produce
these antibodies if the same antigen appears at a later time.
It is, however, pertinent to state here that
B cell differentiation is also stimulated duly by interleukin-2
(IL-2),
secreted by the T4 cells, and by foreign antigens processed by macrophages.
Local Immunity
Local immunity
is usually limited to a given area or tissue of the body.
Natural Immunity
Natural immunity
refers to the immunity programmed in the DNA, and is also known as the
genetic immunity.
It has been observed that there are certain pathogens that fail to infect some species
due to the fact that the cells are not exposed to appropriate environments, for instance : the
‘measles
virus’
cannot reproduce in the canine cells ; and, therefore, dogs do have natural immunity to measles.
Passive Immunity
Passive immunity
specifically refers to the immunity acquired by the introduction of preformed
antibodies
into an unprotected individual. It may take place either through injection or in utero from
antibodies that usually pass from the mother to the foetus
via the placenta. It can also be acquired by thenewborn by ingesting the mother’s milk.