The document discusses immunology, detailing the immune system's response to antigens, including the differences between active and passive immunity. Active immunity involves the host producing its own antibodies following exposure, while passive immunity is short-term and provides antibodies from external sources. It also explains the roles of B and T cells in adaptive immunity, highlighting the processes of humoral and cell-mediated immune responses.

1. By
VIPUL Patil
Assistant Professor
Microbiology
Rabindranath Tagore University

2. Introduction
Immunology it is the branch of biomedical science concerned with the
response of the organism to antigenic challenge.
Defense mechanisms include all physical, chemical and biological
properties of the organism which reduce it’s susceptibility to foreign
organisms.

3. Immunity is the ability of the host to protect itself against foreign
organisms.
Immune system comprises of molecules, cells and tissues that
mediate responses to foreign substances.
What is Immunity?
Functionally these may be divided into those which are static, or
innate to the organism, and those which are responsive, or
adaptive/acquired to potential pathogen.

5. Acquired Immunity
Four characteristics:
It is second line of defense.
Specificity for distinct molecules.
An ability to remember and respond more vigorously to repeated
exposure to the same pathogen.
Self/non self recognition

6. Active Immunity Passive Immunity
Active immunity is a permanent
immunity produced by the antibodies of
the host in response to a direct contact of
an antigen
Passive immunity is a short-term
immunity produced by the introduction
of antibodies from outside to the host
Immunity doesn’t occur immediately. A
time lag occurs for its development
Immunity develops immediately. There is
no time lag
It generates an immunological memory Doesn’t generate immunological memory
When the antigens enter the body
naturally, antibodies and specialized
lymphocytes are induced by the body
Antibodies are passed from a mother to a
fetus through the placenta and to an
infant via mother’s milk.
No side-effects It may cause reactions
Active vs Passive Immunity

8. Adaptive immunity is triggered when a pathogen evades the innate immune system for long
enough to generate a threshold level of an antigen. A typical adaptive immune response includes
several steps:
 The antigen for the pathogen is taken up by an antigen-
presenting cell (APC), such as a dendritic cell or
macrophage, through phagocytosis.
 The APC travels to a part of the body that contains
immature T and B cells, such as a lymph node.
 The antigen is processed by the APC and bound to
MHC class II receptors and MHC class I receptors on
the cell membrane of the APC.
 The antigen is presented to immature helper T cells
and cytotoxic T cells through binding the MHC II
(helper T) or MHC I (cytotoxic T) to T-cell receptors.
 These T lymphocytes mature and proliferate. Helper T
cells activate B cells, which proliferate and produce
antibodies specific to the antigen, while cytotoxic T
cells destroy pathogens that bear the antigen that was
presented to them by the APCs.
 Memory B and T cells are formed after the infection
ends.

10. The adaptive immune response is mediated by B and T cells and creates immunity memory. There are two
subdivisions of the adaptive immune system: cell-mediated immunity and humoral immunity.
Humoral immune response or antibody-mediated response is associated with the B
cells. This immune response is also assisted with helper T cells.
This following points can explain the eventual process:
 Antigens triggers to the body.
 Antigens bind to the B cells present in the blood circulation.
 Helper T cells or Interleukins assist the B cells and initiate B cell proliferation which activates plasma B cells.
 Plasma cells carry antibodies which are antigen-specific and has specific binding receptors of the activated B
cells.
 These antibodies travel throughout the body and bind to the antigens.
 The B cells after destroying the antigens, produce memory cells which in turn provide future immunity when
the same antigen triggers the body again.

11.  T lymphocytes assist the Cell-mediated immunity or cellular immunity
This following points can explain the eventual process:
 Antigen-presenting cells (APCs) will display the antigens present on its surface and binds to T cells.
 Interleukins (secreted by helper T cells) facilitates the activation of T cells.
 Along with the MHC-I and the endogenous antigens, the T cells proliferate and produce the cytotoxic T cells.
 The T cells destroy the infected cells exhibiting antigens.
 In case of exogenous antigens and MHC-II displayed on the plasma membrane together, the T cells trigger to
proliferate helper T cells which release interleukins and cytokines and also arouse the B cells to produce
antibodies against them. This process is also supported by the natural killer cells (NK) and macrophages,
which destroys the antigens.

13. Conclusion
We concluded that both the types of immunity differ in the process
of destroying the pathogens, where antigens specific antibodies are
produced rapidly against the antigens, while in cell-mediated
immunity the pathogens are destroyed through cell lysis.