Class Notes (836,563)
Canada (509,855)
Biology (529)
BLG 230 (36)
Surlon (34)
Lecture

Immune Activation

2 Pages
103 Views
Unlock Document

Department
Biology
Course
BLG 230
Professor
Surlon
Semester
Fall

Description
 Sustained immune activation during HIV infection can ultimately deplete the body’s supply of helper T cells and lead to the collapse of the host’s defences  An untreated HIV infection exhibits distinct phases, in which the loss of helper T cells happens at different rates and appears to be driven by different mechanisms  In the acute or initial, phase, HIV virions enter the host’s body and begin to replicate  HIV gains entry into a host cell by first latching onto the cell-surface protein CD4, then binding to a coreceptor  The coreceptor used by most of the HIV strains responsible for new infections is CCR5 o These viral strains can thus infect dendritic cells, macrophages, regulatory T cells, and especially memory and effector helper T cells  HIV replicates explosively, and the concentration of virions in the blood climbs steeply o At the same time, the concentrations of CD4 T cells plummet, largely because HIV kills them while replicating o Hardest hit are the memory helper T cells in the lymphoid tissues of the gut o Since the gut is both large and vulnerable to penetrations by pathogens, the loss of these T cells is a severe blow to the body’s defenses  The acute phase ends when viral replication slows and the concentration of virions in the blood drops o This slow down may be because that the virus simply runs short of host cells it can easily invade  In addition, the immune system mobilizes against the infection and killer T cells begin to target host cells infected with HIV o The host’s CD4 T cell counts recover somewhat  This slows HIV, but it has not been stopped  As the chronic phase begins, the immune system struggles to recover form its initial losses while continuing to fight the virus o Throughout the chronic phase, the immune system remains highly activated  Chronically activated state of the immune system may enhance some aspects of the host’s response to HIV  It also generates a steady supply of activated CD4 T cells in which HIV can replicate o And it burns through the host’s supply of naive and memory helper T cells by stimulating them to divide and differentiate into short-lived effector cells o Replacement of lost helper T cells ultimately depends on the production of new naive T cells by the thymus o Thymic output declines with age, however and is also impaired by HIV infection o HIV infection also damages the bone marrow and lymph nodes  as the battle goes on, immune system’s capacity to regenerate steadily erodes  viral load climbs again and the CD4 T cell counts fall  Chronic phase ends when the concentration of helper T cells in the blood drops below about 200 cells per cubic millimetre  With few helper T cells left, the immune system can no longer function o The patient develops AIDS o Syndrome is characterized by opportunistic infections with bacterial and fungal pathogens that rarely cause problems for people with robust immune systems  An HIV-infected individual that does not have the effect of anti-HIV drug therapy, if the individual has begun showing symptoms of AIDS, then the individual typically can expect to live two or three more years  AIDS begins when HIV infection has progressed to a point where the immune system does not function properly.  AZT, one of the first anti-AIDS drugs, turned out to be
More Less

Related notes for BLG 230

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit