Miscellaneous Flashcards
what is the epidemiology of HIV/AIDS?
- in general more men are infected than women - could be due to the fact that HIV is spread very well by anal intercourse which is very prevalent in male to male sexual activity
- of those diagnosed in the UK, 30% are women
- sub-Saharan Africa remains the most seriously affected
- homosexual (male sex with men (MSM)) and culturally diverse heterosexual population from sub-Saharan Africa are the two largest groups of people living with HIV
- there is increasing HIV transmission in eastern Europe and Middle East where homosexuality is less accepted and driven underground
- majority of all new infections world-wide are 15-24 year olds
who is most at risk for HIV/AIDS?
- men who have sex with men (unprotected - higher risk)
- heterosexual women (unprotected - higher risk)
- IV drug users
- commercial sex workers
- heterosexual men
- truck drivers (tend to use sex industry more)
- migrant workers (tend to use sex industry more)
- uncircumcised men
what are the routes of administration of HIV/AIDS?
- sexual intercourse (vaginal and anal)
- mother to child transmission
- contaminated blood, blood products and organ donation
- contaminated needles
what are features of sexual intercourse (vaginal and anal) as a route of acquisition of HIV/AIDS?
- world-wide, sexual intercourse accounts for the vast majority of infections
- coexistent STIs especially those causing genital ulceration enhance transmission
what are features of mother-to-child transmission as a route of acquisition of HIV/AIDS?
can occur in utero although the majority of infections take place perinatally or via breast milk
what are features of contaminated blood, blood products and organ donation as a route of acquisition of HIV/AIDS?
risk is minimal in developed countries since the introduction of screening
what are features of contaminated needles as a route of acquisition of HIV/AIDS?
major route of transmission of HIV among IV drug users who
share needles and syringes
what type of virus is HIV?
part of the lentivirus group of the retrovirus family
what does the HIV envelope contain?
HIV envelope contains RNA, capsid (encases the genetic material of the virus) and reverse transcriptase
what is the action of reverse transcriptase?
- has the enzyme reverse transcriptase which allows viral RNA to be transcribed into DNA and thence incorporated into the host cell genome using the enzyme integrase
- since reverse transcription is highly error-prone and due to the high rate of viral turnover this leads to considerable genetic variation and a diversity of viral subtypes or clades
what are the different groups of HIV?
- group M (major)
- group N (new)
- group O (outlying)
what are features of group M HIV? where are its subtypes most common?
• most common
• have subtypes or clades ranging from A-K
• subtype A is most common in West and Central Africa
• subtype B is most common in Europe, North America and
Australia
• subtype C is most common in Southern Africa
where does HIV enter the body?
virus enters via mucosa - vagina, rectum or intestines (at delivery or via breastfeeding in infants)
how does HIV spread within the body?
- local infection within a mucosal macrophage or dendritic cell is established
and then spreads to other cells - as these are antigen presenting cells, some will migrate to local lymph nodes to present antigen to T cells - where infection of T helper cells occurs
- HIV targets CD4 T helper cells
what is the function of CD4 T helper cells?
- CD4 T helper cells act as the bodies coordinators in the specific/acquired immune response
- they are responsible for organising, recruiting and facilitating the maturation of B-antibody producing cells and CD8 T killer cells
what happens on presentation of antigen to CD4 cells?
CD4 cells mature into two types of T helper cell
what is the function of T helper 1 cells?
- produces specific interleukins (IL4, 5, 10, 13) that cause the maturation of B lymphocytes into plasma cells
- the plasma cells then produce specific antibodies e.g. IgG etc. against the specific antigen - allows for a more prolonged and effective antibody response
what is the function of T helper 2 cells?
- produces interferon alpha and TNF
- these cytokines activate further CD8 cells, turning them into Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells
- CTLs then produce then enzyme perforin that directly kills cells with the antigen on or in
- note: IFN alpha is an important cytokine in the bodies defence against TB
what is the HIV envelope glycoprotein?
gp120
what does HIV bind to?
binds, via its gp120 envelope glycoprotein, to CD4 receptors on:
- helper T lymphocytes
- monocytes
- macrophages
- neural cells
what is responsible for HIV entry into cells?
interaction between CD4 and HIV glycoprotein gp120 together with host chemokine CCR5 or CXCR4 co-receptors is responsible for HIV entry into cells
what is gp160 made of?
gp120 and gp41
what is the mechanism of viral replication within CD4 T helper cells?
- glycoproteins on the HIV molecule (gp160 made up of gp120 and gp41) allow it to attach and fuse onto the CD4 and CCR5 receptors
- the viral capsid then enters and enzymes and nucleic acids are uncoated and released
- using reverse transcriptase the single stranded RNA is converted into double stranded DNA
- viral DNA is then integrated into the host cells own DNA by integrase enzyme
- when the infected cell divides the viral DNA is read and transcribed and long chains of viral proteins are made
- viral RNA is spliced and protein chains are cleaved and reassembled by the protease enzyme into individual proteins that combine to form a working virus
- budding occurs where the immature virus pushes out of the cell taking with it some cell membrane of the T helper cell
- immature virus breaks free to undergo more maturation and is then able to infect other CD4 cells
where do infected T cells go once they have been infected by HIV?
- infected T cells then leave the lymph node and infection spills into the blood stream resulting in viraemia and the exponential rise in T cell infection occurs
- replication of HIV in the CD4 T cells results in cell death