INTRO TO VIRAL INFECTIONS
WHAT ARE VIRUSES?
Submicroscopic particle (size is measured in
nanometers), (can use electron microscope)
Basic structure: core of DNA or RNA
o RNA viruses are more numerous than DNA
viruses
o DNA or RNA is packed in protein coat or capsid
and some virus’s capsid is surrounded by outer
envelope such as glycolipids and proteins.
Intracellular pathogens
o They will rely on the host cells to survive. Because
they will live inside the cells of the host. They are
going to rely on host cells for replication and
survival. basically speaking, if the virus does not
have a host, it means it’s dormant or hindi niya
kayang mabuhay mag-isa, kailangan niya ng host
cell para mag-survive.
Bacteria – comparable to blood cells that is measured in
micrometers. Use the usual compound microscope
PATHOGENECITY OF VIRUSES
VIRION – it will infect host cell by attaching to a specific
receptor
The virus once it enters our body will look for its target cell.
Each of the viruses has a target cell
1. Look for target cell
2. Penetrate - enters inside the cell membrane and
release its nucleic acid, either RNA or DNA. Once it
releases, nucleic acid will direct the host machinery to
produce more viral nucleic acid and proteins
3. Nucleic acid and protein will assemble inside the cell
to form intact virus. Once there’s intact virus, virus
will be released thru cell lysis or budding of cells
surface.
For viruses, once they infects the cell, it also leads to the
destruction of the cell kaya bumababa yung count ng ating
cells
For example, HIV virus, the target cell is CD4 T cells or T
helper cells. Once it attacks all the CD4 T cells (they need
it for replication), mauubos yung CD4 T cells. Once the
maubos, they will go and attack monocyte
INNATE IMMUNITY AGAINST VIRUSES
Nonspecific immunity
First line of protection
Interferon-a and Interferon-b
o These is produced following the recognition of the
toll like receptors
o Inhibits viral replication
By inducing transcription of several genes
that will code for proteins with antiviral
activity.
o Enhances activity of NK cells
Once of the cell in innate immune system that
can specifically react w/ viruses
Main function of NK cells is to bind to the
virus infected cells and release cytotoxic
proteins like perforin and granzymes, which
cause the cells to die and release their virus
particles. These cell-free virions are now
accessible to antibody molecules.
Perforin – substance that can create pores to
our virus, causing the entry of extracellular
fluid, thus, cells that is infected with virus can
lyse
HUMORAL DEFENSE MECHANISM
B cells and plasma cells
In this process, antibodies specific for a
component of the virus will attach to the
receptor on the host cell membrane will
bind to the virus and prevent it from
attaching to and penetrating the cell.
Secretory IgA will neutralize viruses in
the mucus secretions
gG and IgM will attach to the virus in the
blood stream, thus preventing the
dissemination of infection
DOMAOAL, A. 2
IgG and IgM can also activate the
complement system
o Produces virus specific antibodies
o Ab prevents spread of viral replication
through neutralization
o IgG: promotes phagocytosis thru
opsonization
o IgM: Agglutinates viral particles
CELLULAR DEFENSE MECHANISM
Upon activation of CD4+ T helper cells and
cytokines, CD8+ Cytotoxic T cells become
programmed to expand in number and attack the
virus infected cells.
Cytotoxic T cells produce proteins and proteases
o Perforin
o Granzymes
It will lead to the elimination of the
intracellular viruses that is required for their
replication
Increase 50,000 times its original number
Cellular defense mechanism will enter once humoral
defense mechanism is already compromised, that’s
when CD4 & CD8 enters
STRATEGIES ON HOW VIRUSES ESCAPES
IMMUNE MECHANISMS
They undergo frequent genetic mutations
o Produces new viral antigens – not
recognized immediately by initial immune
response
o Best example: COVID19
o Compared to bacteria, parasites and fungi, viruses are
frequent to undergo genetic mutations bec. they have
nucleic acid (DNA or RNA)
o One of the reasons why a person who was already
infected with the virus before can still be reinfected.
The reinfection does not mean that the vaccine was not
effective but the virus may be of a new strain. This is
because some vaccines are only effective to the
original strain and not on new strains.
Some viruses can evade actions of the
component of the immune response
o For example, the Hepatitis C virus (HCV) can block
the degradation of viral RNA that is induced by
interferons. Interferons will not work against HCV
Viruses can evade the hosts defense by
suppressing the immune system
o For example, cytomegalovirus and human
immunodeficiency virus (HIV) can reduce the
expression of major histocompatibility complex
molecule on the surface of virus infected cells
making them less likely to be recognized by T cells
LABORATORY TESTING FOR VIRAL INFECTION
Serologic testing – help monitor the course of
infection and can also detect past infection and assess
immune status.
Virus specific IgM Antibodies
o Indicates current or recent infection
o Specific IgM antibody in newborns indicates
congenital infection with virus
o IgM Abs in newborn is not normal. Because IgM
cannot cross the placenta, bec. it’s bigger
o The mother is previously infected and been pass to the
baby
IgG Antibodies to the virus
o Indicates current or past infection and in
most cases immunity
o IgG antibodies in newborns are mainly
maternal antibodies
o IgG can cross the placenta