2 Overview of Immune Response
Following the injection of the vaccine into a patient, the antigens
contained within the vaccines are processed to develop an immune
response. Upon initial introduction of the antigens, the body must
recognize the antigens introduced by the vaccine and mount an
immune response toward them. Although the body’s innate
immune response can mount an initial response to the antigens,
the goal of a vaccine is to develop a longer-lasting response from the
body’s adaptive immune system.
The initial stages of this process occur when the cells of the
body’s immune system recognize epitopes or moieties associated
with the vaccine antigen. Antigen-presenting cells (APCs) such as
dendritic cells will recognize and phagocytose the vaccine particles
and process them internally. As a result of this process, fragments of
the digested antigen are displayed on the APC’s surface in association with the major histocompatibility (MHC) II protein (Fig. 1).
The APC can then travel to the body’s lymph nodes to help develop
a stronger and longer-lasting humoral immune response against the
vaccine antigen. Alternative B cells can recognize antigens that have
not been processed by an APC and mount an immune response.
These antigens, also known as T cell-independent antigens, include
molecules such as bacterial capsular polysaccharides. When this type
of immune response is generated, it is typically immunoglobulin
(Ig)M-biased and demonstrates a weaker and shorter-lasting
immune response compared to that obtained through the involvement of T cells.
Once the APC has reached the lymph nodes, it is capable of
participating in T cell-dependent maturation of B cells. Both of
these cells travel to lymph nodes to play a role in the adaptive
immune response. During the initial stage of the process, receptors
on the surface of CD4+ Helper T cells interact with the MHCII
receptor of the APC and the processed vaccine antigen that is
associated with it. This interaction activates the CD4+ T cell and
can enable it to stimulate reproduction and activation of B cells.
When the activated T cell interacts with a B cell displaying the
appropriate antigen, it releases cytokines that promote proliferation
of the B cell population and their subsequent maturation into
antibody (typically IgG)-secreting plasma cells. In addition, this
interaction also promotes a process known as somatic hypermutation in which a great degree of mutation of the variable region of
the B cell antibody is achieved. As a consequence of this process,
antibody variants processing greater degrees of affinity for the
antigen can be generated to develop a highly potent and specific
immune response. Once these immune cells have been generated,
they can either disseminate to become effector cells or remain in
lymph nodes as memory cells to enable the body to mount a rapid
response if a similar infection occurs.
4
Andrew Hill et al.
Following the injection of the vaccine into a patient, the antigens
contained within the vaccines are processed to develop an immune
response. Upon initial introduction of the antigens, the body must
recognize the antigens introduced by the vaccine and mount an
immune response toward them. Although the body’s innate
immune response can mount an initial response to the antigens,
the goal of a vaccine is to develop a longer-lasting response from the
body’s adaptive immune system.
The initial stages of this process occur when the cells of the
body’s immune system recognize epitopes or moieties associated
with the vaccine antigen. Antigen-presenting cells (APCs) such as
dendritic cells will recognize and phagocytose the vaccine particles
and process them internally. As a result of this process, fragments of
the digested antigen are displayed on the APC’s surface in association with the major histocompatibility (MHC) II protein (Fig. 1).
The APC can then travel to the body’s lymph nodes to help develop
a stronger and longer-lasting humoral immune response against the
vaccine antigen. Alternative B cells can recognize antigens that have
not been processed by an APC and mount an immune response.
These antigens, also known as T cell-independent antigens, include
molecules such as bacterial capsular polysaccharides. When this type
of immune response is generated, it is typically immunoglobulin
(Ig)M-biased and demonstrates a weaker and shorter-lasting
immune response compared to that obtained through the involvement of T cells.
Once the APC has reached the lymph nodes, it is capable of
participating in T cell-dependent maturation of B cells. Both of
these cells travel to lymph nodes to play a role in the adaptive
immune response. During the initial stage of the process, receptors
on the surface of CD4+ Helper T cells interact with the MHCII
receptor of the APC and the processed vaccine antigen that is
associated with it. This interaction activates the CD4+ T cell and
can enable it to stimulate reproduction and activation of B cells.
When the activated T cell interacts with a B cell displaying the
appropriate antigen, it releases cytokines that promote proliferation
of the B cell population and their subsequent maturation into
antibody (typically IgG)-secreting plasma cells. In addition, this
interaction also promotes a process known as somatic hypermutation in which a great degree of mutation of the variable region of
the B cell antibody is achieved. As a consequence of this process,
antibody variants processing greater degrees of affinity for the
antigen can be generated to develop a highly potent and specific
immune response. Once these immune cells have been generated,
they can either disseminate to become effector cells or remain in
lymph nodes as memory cells to enable the body to mount a rapid
response if a similar infection occurs.
4
Andrew Hill et al.