Lecture 20 Flashcards
What is HIV?
human immunodeficiency virus
What does HIV attack?
immune system
- CD4 (t-helper) cells
What does the CD in CD4 mean?
clusters of differentiation
How does CD4+ work?
- cytokine signaling with B cells
- interacts directly with antigens
- bind MHC class II molecules on B cells and APCs
- T-helper secretes costimulatory molecule
What do T-helper cells produce?
cytokines into
-> T-helper 1 cells
-> T-helper 2 cells
-> T-helper 17 cells
-> memory cells
What do T-helper 17 cells produce? What does it contribute to?
IL-17
- contributes to inflammation
What do T-helper 1 cells produce? What does it do?
IFN-gamma
- activates macrophages
- enhances complement
- stimulate antibody production that promotes phagocytosis
What do T-helper 2 cells release? What does it do?
IL-4 cytokine
- activates B cells to produce IgE
- activates eosinophils
How are TH1 cells involved in HIV/AIDS?
- cell-mediated immunity
- activation of cytotoxic T cells and macrophages
- HIV leads to depletion of CD4+ TH1 cells, weakening the immune system’s ability to combat intracellular pathogens
How are TH2 cells related to HIV/AIDS?
- associated with humoral immunity
- helps B cells produce antibodies
- balance between TH1 and TH2 is disrupted in HIV (TH2 more dominant) = contributes to reduced cell-mediated immunity
How are TH17 cells related to HIV?
- mucosal immunity (defending against bacterial and fungal infections at epithelial barriers)
- HIV can impair TH17 cells (weakening of mucosal defenses and gut barrier integrity) = systemic inflammation and microbial translocation
How are memory cells related to HIV?
- HIV establishes reservoirs in memory CD4+ T cells (latent virus)
- hard to eradicate virus entirely
- memory cells harbor latent HIV and can reactivate causing ongoing infection
What is the structure of HIV?
- genus: lentivirus
- retrovirus (reverse transcription)
- 2 identical + stranded RNA genome molecules
- phospholipid envelope
- gp120 glycoprotein spikes
- capsid
How does HIV infect the body?
- spread by dendritic cells and carried to the lymphoid organs
- contacts activated T cells
- gp120 combines with CD4+ receptor and CCR5 or CXCR4 coreceptors
- CD4 molecules are carried on Th cells, macrophages, and dendritic cells
- virus fuses and enters into the cell.
How does HIV work inside the cell?
- viral RNA is transcribed into DNA using reverse transcriptase
- DNA is integrated into the host’s chromosomal DNA
- virus undergoes rapid antigenic changes and a high rate of mutation
What is an active infection?
new viruses bud from the host cells
What is a latent infection?
DNA is hidden in the chromosome as a provirus
- some become memory T cells that serve as the reservoir for HIV
What are the characteristics of HIV-1?
- related to viruses that infect chimpanzees and gorillas
- 99% of cases
- group M (majority) accounts for 90%
What are the characteristics of HIV-2?
- not often encountered outside of West Africa
- less pathogenic than HIV-1
- longer asymptomatic period with lower viral load and mortality rate than HIV-1
What suppresses viral numbers?
cytotoxic T lymphocytes (CTLs)
How is HIV transmitted?
- can survive 6 hours outside a cell and 1.5 days inside
- sexual contact
- breast milk
- transplacental infection of a fetus
- blood-contaminated needles
- organ transplants
- artificial insemination
- blood transfusion
- anal-receptive intercourse
What are the phases of HIV infection?
Phase 1: asymptomatic or lymphadenopathy
Phase 2: CD4+ cells decline steadily (only a few infected cells release the virus)
Phase 3: AIDS develops, CD4+ is below 200 cells/microliter
Who are long-term survivors of HIV exposure?
- low viral load
- effective CTLs
What are the symptoms of HIV infection?
Acute stage: flu-like symptoms, high viral load
Chronic stage: asymptomatic or mild symptoms, virus continues to replicate
AIDS: severe immune system damage, opportunistic infections occur
