immunology of HIV Flashcards
acute HIV syndrome and seroconversion
2-6 weeks after initial infection
active virus replication and can be detected in blood and CSF
lymphoid organs seeded with virus
seroconversion = production of anti-HIV antibodies
occurs 6-9 weeks after exposure
window period: when patient is viremic and contagious, but tests are all negative
latent phase (asymptomatic infection)
can last 10 years
nearly undetectable in serum or blood cells, but replication is active in lymphoid tissues
to go into AIDS, requires T cell activation by antigen or cytokines
ARC
AIDS-related complex
some patients go through this phase prior to AIDS
persistent fevers, night sweats, weight loss, etc.
yeast infections and herpes
AIDS
recurrent infections with opportunistic pathogens tumors (Kaposi's sarcoma, NHL) wasting dementia CD4 count drops below 200
pathogenesis of HIV/AIDS
virus gets into bloodstream
attaches to CD4 on T cell or phagocytes by gp120
conformational change in gp120 promotes fusion of viral envelope with plasma membrane of host cell
once inside, HIV genome reverse transcribed into host cell DNA
cytokines can trigger activation of NFkB, which controls transcription of viral genes
what cytokines trigger HIV transcription/replication in T cells
TNF alpha
IL-2
what cytokines trigger HIV transcription/replication in monocytes and macrophages
IL-1 IL-3 IL-6 TNF alpha IFN gamma GM-CSF
what do NFkB and SP1 bind to
HIV LTRs (long terminal repeats) –> viral gene transcription
why may macrophages act as in vivo reservoir of HIV
not as prone to lysis as T cells
transport virus through body
contribute to AIDS dementia complex/AIDS encephalopathy
CD4:CD8 ratio
when patient goes into full blown AIDS, CD8 stays the same while CD4 drops
healthy ratio = 2
AIDS ratio = 0.5
how are T cells killed in HIV
direct lysis by budding HIV
virus production interferes with cellular protein synthesis –> cell death
syncytia formation of infected cells with uninfected cells
destruction of lymphocytes via binding of free gp120 –> antibody response leading to ADCC
CTL-mediated destruction
besides T cell depletion, what else accounts for immunosuppression in HIV/AIDS
binding of free gp120 to CD4 protein of uninfected T cells, inhibiting them from binding class II MHC and reacting to antigen destruction of follicular dendritic cell network alter lymphoid organs
why is immunity not protective against HIV
latent period–remains undetected
high mutation rate
Nef protein downregulates expression of class I MHC, making cells invisible to CTLs
most frequent cause of death in AIDS patient
Pneumocystis carinii
ELISA
screening test
utilizes HIV antigens from H9 cell line
false positives are common in multiparous females or patients with autoimmune diseases
if positive, test is repeated
