This essay covers all the lecture content of lecture 8 of Immunology of Human Disease. It focuses on two main aspects: the intrinsic, innate and adaptive immune barriers to viral infection; and pattern recognition. To maintain health, the immune system and body defences are coordinated to block a ...
What are the intrinsic, innate and adaptive immune barriers to viral infection?
To maintain health, the immune system and body defences are coordinated to block a
majority of infections. The immune system includes the adaptive and innate immune systems
and cells like APCs, B cells and T cells, antibodies and interferons. Body defences include the
skin, the mucus and stomach acids. Breaching these initial barriers results in host cell infection
and disease occurrence. In order to survive in the host, viruses must be immunologically fit.
The virus must survive in the host cell by using its machinery for translation and transcription
as it does not have its own mitochondria and ribosomes. Successful viruses must avoid host
defences to be able to replicate and transfer to a new host cell. In this essay, we will discuss
the intrinsic, innate and adaptive immune barriers to viral infections.
Coordinated host responses to infection include a continuous response via the physical
barriers like the skin, respiratory tract, urogenital tract and eyes, an immediate response
called the intrinsic response which are cell autonomous responses that don’t require the
transcription and translation of new elements, like autophagy and interferons. Other
responses involve the innate response which results minutes to hours after the infection and
includes NK cells, genes and complement, and finally the adaptive response which occurs
hours and days after the infection, it is characterised by T and B cells adapted to the specific
virus and are antigen-dependent.
The skin barrier is formed by an outer layer of dead keratinised cells providing a physical
armour against viral infection. It inactivates viral particles by desiccation, acids and other
inhibitors. The respiratory tract has mucus which traps viral particles, swallows the virus and
degrades it via stomach acids. High levels of IgA and antibodies are present in this barrier. The
alimentary tract is made of saliva, extreme pH, proteases and bile detergents that do not
allow viruses to survive. The urogenital tract has a low pH which is modulated upon bacterial
invasion or the menstrual cycle allowing viral infections especially in the presence of tears.
Like the alimentary tract’s saliva, the eye has tears which contain small amounts of lysosomal
enzymes and antibodies. However, before passing through these initial barriers, viruses need
to find cells susceptible and permissive of their entry. They must bind to specific receptors,
allowing their entry into the cell which must contain all the proteins required for the virus to
replicate.
The intrinsic defences is the detection and alarm component of the immune system. It detects
foreign bodies, sound an alarm and allow surrounding cells to enter an antiviral state and
recruit professional APCs. It distinguished between self and non-self in a timely manner, as
too much activation is deleterious to the organism causing inflammation and tissue damage.
Other intrinsic responses include cytopathic effects which allow the aggregation of
intracellular components, allowing recognition by phagocytic cells. Apoptosis effectively
reduces viral propagation and autophagy allows the recycling of cellular components to target
incoming virus to lysosomes.
Soluble innate mediators of the innate immune response include cytokines, chemokines and
interferons. Chemokines activate signalling pathways and recruit immune cells at the site of
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