science

HIV tropism

HIV tropism is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand HIV tropism rather than just read about it. In short: HIV tropism refers to the cell type in which the human immunodeficiency virus (HIV) infects and replicates. HIV tropism of a patient's virus is measured by the Trofile assay.

Key takeaways

HIV tropism belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HIV tropism to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HIV tropism from memory before moving on to harder problems.

Reference excerpt

HIV tropism refers to the cell type in which the human immunodeficiency virus (HIV) infects and replicates. HIV tropism of a patient's virus is measured by the Trofile assay. HIV can infect a variety of cells such as CD4+ helper T-cells and macrophages that express the CD4 molecule on their surface. HIV-1 entry to macrophages and T helper cells is mediated not only through interaction of the virion envelope glycoproteins (gp120) with the CD4 molecule on the target cells but also with its chemokine coreceptors. Macrophage (M-tropic) strains of HIV-1, or non-syncitia-inducing strains (NSI) use the beta-chemokine receptor CCR5 for entry and are thus able to replicate in macrophages and CD4+ T-cells. These strains are now called R5 viruses. The normal ligands for this receptor—RANTES, macrophage inflammatory protein (MIP)-1β and MIP-1α—are able to suppress HIV-1 infection in vitro. This CCR5 coreceptor is used by almost all primary HIV-1 isolates regardless of viral genetic subtype. T-tropic isolates, or syncitia-inducing (SI) strains replicate in primary CD4+ T-cells as well as in macrophages and use the alpha-chemokine receptor, CXCR4, for entry. These strains are now called X4 viruses. The alpha-chemokine SDF-1, a ligand for CXCR4, suppresses replication of T-tropic HIV-1 isolates. It does this by downregulating the expression of CXCR4 on the surface of these cells. Viruses that use only the CCR5 receptor are termed R5, those that only use CXCR4 are termed X4, and those that use both, X4R5. However, the use of a coreceptor alone does not explain viral tropism, as not all R5 viruses are able to use CCR5 on macrophages for a productive infection.

Trofile assay The Trofile assay is a blood test that identifies the tropism of a patient's HIV. A molecular assay, Trofile was developed by Monogram Biosciences for use in HIV treatment. The assay's purpose is to identify the tropism of an individual patient's HIV strain – R5, X4, or a combination of these known as dual/mixed (D/M). The results show whether the patient is infected with virus that enters cells using the R5 co-receptor, the X4 co-receptor, or both (dual/mixed). Patients with strains of HIV that prefer the R5 receptor tend to remain healthy longer than those with the strains that prefer X4. However, over the course of the disease, a patient's viral population may undergo a "tropism switch" from R5 to X4.

References

External links HIVcoPred A server for prediction of HIV coreceptor usage (CCR5). PLoS ONE 8(4): e61437 Monogram Biosciences' Trofile assay: Monogram Biosciences' Trofile assay website Four Studies Affirm Significance Of Monogram's Trofile HIV Co-Receptor Tropism Assay Archived 2011-05-16 at the Wayback Machine from Medical News Today, August 14, 2006 Scientific Data Highlights Pivotal Role Of Monogram's Molecular Diagnostics In Development And Use Of New HIV Treatments Archived 2011-05-16 at the Wayback Machine from Medical News Today, March 7, 2007

Illustrations

Worked examples

Example 1 — a first encounter with HIV tropism

Start with the simplest possible case. Write down what HIV tropism claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to HIV tropism before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about HIV tropism ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of HIV tropism

In research: HIV tropism appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses HIV tropism in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: HIV tropism is common in secondary-school and first-year university syllabi. It links to neighbouring topics HIV/AIDS, so understanding it makes those chapters shorter.
In everyday life: Look for HIV tropism outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study HIV tropism in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HIV tropism means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain HIV tropism out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HIV tropism in simple terms?

HIV tropism refers to the cell type in which the human immunodeficiency virus (HIV) infects and replicates. HIV tropism of a patient's virus is measured by the Trofile assay.

Why does HIV tropism matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study HIV tropism?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on HIV tropism.