Lecture 22 - HIV (1) Flashcards

Question

How do Antigen presenting cells (APCs) present foreign material, and to which cells?

Answer 1

APCs present foreign antigens to CD4+ T cells in the context of MHC II (major histocompatibility complex) alpha chain and the T cell receptor beta chain (TCR) Similar process for CD8+ T cells and MHC class I Both CD4 and CD8 make very robust response to HIV, its the over-exuberant immune response that makes people sick

Answer 2

Partial immune control of HIV refers to the ability of the immune system to partially suppress HIV replication in the body, leading to lower viral load levels and slower disease progression. This is typically seen during the chronic phase of HIV infection, which can last for many years. During this phase, the virus replicates slowly and the immune system mounts a response, which results in a decline in viral load levels. However, the virus is not completely eradicated

Answer 3

1. Initial immune response - HOURS/DAYS 2. Acute phase: a rapid increase in HIV viral load, which is accompanied by a surge in the number of activated CD4+ T cells. During this phase, the immune system also mounts a specific response against HIV by producing antibodies and cytotoxic T lymphocytes (CTLs) that can recognize and kill HIV-infected cells. - WEEKS/MONTHS 3. Chronic phase: a stable or slowly increasing viral load and a gradual decline in the number of CD4+ T cells. During this phase, the immune response against HIV becomes less effective, with HIV-specific CTLs becoming exhausted and antibodies becoming less able to neutralize the virus - YEARS 4. AIDS: This occurs when the immune system is severely compromised, and opportunistic infections and cancers can develop.

Answer 4

Sequence variation: * Lack of recognition (both CTL and antibody) * Antagonism Altered antigen presentation * Down regulation of MHC class I molecules by Tat, Vpu and Nef Loss of effector cells * Clonal exhaustion * Loss of CD4 T cell help * Replicative senescence Latency * Particularly in resting T-cells, macrophages and astrocytes Privileged sites of viral replication * Brain, testis, gastrointestinal tract

Answer 5

A newly acquired infection is defined as an infection diagnosed in a patient who has had a negative HIV test in the past 6 months. Newly diagnosed infection is a positive result in a patient whose time of acquiring the virus is not clear as there are no recent negative tests.

Answer 6

It's the gp120 envelope glycoprotein that undergoes conformational changes, however this then also induces conformational changes in gp41 which is critical to fusion of the viral and cell membranes.

Answer 7

Those individuals who are heterozygous for the delta 32 CCR5 mutation express a significantly lower level of CCR5 on their CD4+ cells. This makes these cells somewhat “harder” to infect. Thus what you find that these individuals don’t have any greater level of protection from infection, however once they are infected, the disease course tends to be much slower compared to those individuals who are homozygous for wild type CCR5. Individuals who are homozygous for the delta 32 CCR5 mutation express no CCR5 on their cell surface. They are very resistant to infection. This is because the major transmitted strain of HIV is R5.

Answer 8

Lymph nodes are an important secondary lymphoid tissue where CD4 T cells reside and can recognise antigens presented by APCs and become activated. Fibrosis of the lymph node would result in abnormal scarring and deposition of collagen, and the lymph node would not function effectively. In this way, there would be ineffective activation of T cells, and therefore reduced proliferative signalling.

Lecture 22 - HIV (1) Flashcards

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