Immunology

1. P R E S E N T E D T O : D R A S M A Y A Q O O B
P R E S E N T E D B Y : M I R Z A A B D U L L A H &
M . S H A H J A H A N
S U B J E C T : ( I M M U N O L O G Y )
C L A S S : A D P B I O C H E M I S T R Y 5 T H S E M E S T E R
D E P A R T M E N T : I N S T I T U T E O F
B I O C H E M I S T R Y , B I O T E C H N O L O G Y &
B I O I N F O R M A T I C S
T H E I S L A M I A U N I V E R S I T Y O F B A H A W A L P U R
Body defense System against
Viral Infections

2. How a Virus invade into a Host cell
 A virus needs to invade a living cell to replicate. A viral
infection occur when a virus invades the body and can
need respectable symptoms.
 The virus particles which is called Virion consist of viral
genome that made up of ( DNA & RNA) and is enclosed
in a protein shell called Capsid.
 Some viruses have envelope around capsid that contains
lipids and protein including glycoproteins and viral
receptor proteins known as Spikes.
 The virion uses surface protein of capsid and
glycoproteins of envelop to attached to host cell .

3.  After entering the cell , virion turns into a virus factory.
The virus utilized the host protein formation and
replication function which is used to assembling new
viruses.
 Multiple copies of viruses are released from host cells
and spread to near by cells to keep the cycle.

5. Strategies to prevent Viral infection
Now the body can perform several process to stop the viral
infection to be occur in body. For that purpose Body can
perform Rapid response which involved the following
processes in Innate Immunity.
 Interferon:
 When a virus infects a cell , cell produce and release
signaling proteins called “ Interferon” which are type of
Cytokines.
Interferon Natural Killer
Cells
Antigen
Present cells

6.  Interferon acts as warning signal to neighboring cells.
They act by binding to IFN receptors by near by
unaffected cells. In response cell producing cell
producing viral proteins which prevent the virus from
replicating of cells in the event of infection. Interferon
also plays an important function in immune system .
 They induce near by cells to increase the expression of
MCH-Class I molecule on its surface. MCH-I has two
signaling functions:
 They present antigen to adaptive immune cells
 They present antigens to innate immune cells.

7. Interferon

8. Natural Killer Cells (NKC)
 Natural killer (NK) cells are naturally occurring, that
have receptors that recognized the antigen on MCH-
Class I molecule. The absence of MCH-Class I molecule
play an important role in the immune response of NK
cells.
 Usually cells expressed sufficient MCH-class I on their
surface for T-cells to be able to recognized them if they
become infected. However viruses can prevent infected
cells to synthesizing the molecule. As a result there are
few MHC- Class I molecule on cell surface which causes
the infected cell to evade capture by T-cells.

9.  The patrolling NK cells recognized the absent of MCH-
class I and released toxic substances such as
Granzymes and Perforins which kills virus infected
cells.

10. Antigen Presenting Cells
 Infected cells can also be removed by macrophages.
These are done by ingesting free viruses by a process
called Phagocytosis.
 Macrophages surrounds and engulf the virus.
Macrophage than breaks the virus down by mixing it
with digested enzymes stored in vesicle called “
Lysosomes”.
 The degraded viral material is then released from cell as
waste. Macrophages are antigen presenting cells which
means that they are able to capture, process and antigen
to pathogens.

11.  Another type of antigen presenting cell is Dendritic
cells which approach the innate and adaptive immune
response.

12.  If the innate immune response is unable to control
infection , then adaptive immune response involves.
 T-cells:
 Viral fragments presented on MHC-class I molecule on
the surface of infected cells attracts cytotoxic T cells.
These cells also known as cd8+ T-cells are able to kill
infected cells.
 There are specific T-Cell receptor cytotoxic T-cell
interact with antigen loaded MHC- complex. In
response the complex released cytotoxic factor that
induces cell lysis or apoptosis ( that is programmed cell
death of the infected cell). Macrophages then engulf
dead cells and released as waste.
ADAPTIVE IMMUNE SYSTEM
T - cells B-cells

14. B-cells:
 B-cells also fight against viral antigen however rather
than targeting antigen & killing infected cells produce
specific antibodies. Antibodies are proteins that are
produced in response to specific pathogenic proteins (
The Antigen).
 Before antibodies are produced B and T cells needs to
interact. The B-cells needs to undergoes several steps
to presented the viral antigen on its surface.
o B-cells receptors recognized viral antigen. The B-cells
internalized the antigen and presented of MHC-class II
on B-Cell surface.
o Before T-cell recognition occur CD4+ T cell also known
as T-Helper cell need to interact viral antigen with
same specificity.

15.  The antigen is presenting on the surface of dendritic
cells by MHC-class II class molecules. These entire
process is turned to priming as stimulant the
maturation of CD4+ antigen bind with T-Cell receptor
on CD8+ T-cell. This interaction is called Linked
Recognition.
 And it is the final step to fully activate the B-cell. The
activated B-cells keep rised the long lasting memory B-
cells & Plasma cells.
 Memory cells forms the basis of immunologic
response. They have the ability to recognized the
antigen after its initial exposure.

16. Antibodies:
mechanism used by antibodies to eradicate viruses are:
 Neutralization:
Antibody can neutralize free virus particles to
unable them to infect host cell.
 Opsonization:
Antibodies can marked free viruses for
phagocytosis in a process called Opsonization.
 Activation of Complement System:
The complement system activates through a
triggered-enzyme cascade. In such a cascade, an
active complement enzyme generated by cleavage of
its zymogen precursor then cleaves its substrate,
another complement zymogen, to its active
enzymatic form.

17.  Activation of NKC:
Natural killer cells express various activating,
costimulatory, and inhibitory receptors that can be
targeted to improve NK cell cytotoxicity (Table 1). One
such receptor is CD16, which binds to Fc region of
antibodies and promotes antibody-dependent cell-
mediated cytotoxicity (ADCC) of tumor cells.