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AIDSinfo Glossary Search

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R5-Tropic Virus Audio (En español)

Also known as: M-Tropic Virus

A strain of HIV that enters and infects a host cell by binding to the CCR5 receptor on the host cell. To enter a host cell, HIV must first attach to a CD4 receptor, then attach to either the CCR5 or CXCR4 receptor, and finally fuse its membrane with the host cell membrane. HIV is usually R5-tropic (uses CCR5) during the early stages of infection, but the virus may later switch to using either only CXCR4 or both CCR5 and CXCR4. Antiretroviral (ARV) drugs in the CCR5 inhibitor drug class block HIV from attaching to the CCR5 receptor, preventing HIV entry into the host cell.

See Related Term(s): CCR5, CCR5 Antagonist, CD4 Receptor, CD4 T Lymphocyte, CXCR4, Dual-Tropic Virus, X4-Tropic Virus

Randomized Trial Audio (En español)

A type of clinical trial in which participants are assigned by chance (randomized) to treatment and control groups, or among various treatment groups. Randomization produces groups that are similar overall in terms of general characteristics, such as age or gender, and other factors that might affect the disease or condition being studied. Having groups that are as similar as possible at the start of a clinical trial allows researchers to conclude with a certain level of confidence whether one treatment is better than another at the end of the trial.

See Related Term(s): Clinical Trial, Control Arm

Rapid Test Audio (En español)

A type of HIV antibody test used to screen for HIV infection. A rapid HIV antibody test can detect HIV antibodies in blood or oral fluid in less than 30 minutes. A positive rapid HIV antibody test must be confirmed by a second, different antibody test (a positive Western blot) for a person to be definitively diagnosed with HIV infection.

See Related Term(s): Antibody, Enzyme-Linked Immunosorbent Assay, Western Blot


Also known as: Viral Rebound

Receptor Audio (En español)

A protein that is located inside or on the surface of a cell and that binds to a specific substance, such as a hormone, antigen, virus, or neurotransmitter. The binding of the substance to the cell receptor causes a change in the activity of the cell. In order to enter a host cell, HIV must first bind to receptors on the host cell.

See Related Term(s): CD4 Receptor

Recombinant Audio (En español)

DNA produced in a laboratory by joining segments of DNA from different sources. Recombinant can also describe proteins, cells, or organisms made by genetic engineering.

See Related Term(s): Genetic Engineering

Rechallenge Audio (En español)

Restarting a drug that was stopped because it was considered the likely cause of an adverse effect. When the drug is restarted, the person is closely monitored for any signs of the adverse effect.

Red-Band Gingivitis

Also known as: Linear Gingival Erythema

Red Blood Cell Audio (En español)

Also known as: Erythrocyte, Red Blood Corpuscle

Blood cells that carry oxygen to all parts of the body. Red blood cells have a high concentration of hemoglobin, a protein that binds to oxygen from the lungs and that gives blood its red color.

Red Blood Corpuscle

Also known as: Red Blood Cell

Red Eye

Also known as: Conjunctivitis

Refractory Audio (En español)

Resistant to treatment. For example, a refractory disease or condition is one that is not responding to treatment.


Also known as: Treatment Regimen

Regimen Simplification Audio (En español)

Also known as: Treatment Simplification

Making changes to an HIV treatment regimen to make medication adherence easier. Simplifying a regimen can include reducing the number of antiretroviral (ARV) drugs in a regimen or changing to a drug that offers once-daily dosing. Other changes can include switching to ARV drugs that cause fewer adverse effects or to ARV drugs that can be taken without food. Regimen simplification can improve a person’s quality of life, help maintain long-term adherence, help prevent toxicities that may develop with long-term drug use, and reduce the risk of treatment failure.

See Related Term(s): Adherence

Regulatory T Cell

Also known as: Regulatory T Lymphocyte

Regulatory T Lymphocyte Audio (En español)

Also known as: Regulatory T Cell, Supressor T Cell, Supressor T Lymphocyte

A type of lymphocyte. Regulatory T lymphocytes (regulatory T cells) prevent the immune system from becoming over-active during an immune response and from attacking normal cells.

See Related Term(s): T Lymphocyte

Relapse Audio (En español)

The recurrence of a disease after a period of remission or apparent recovery.

See Related Term(s): Remission

Relative Contraindication Audio (En español)

When a particular treatment or procedure is somewhat inadvisable because there is a higher risk for complications.

See Related Term(s): Contraindication

Remission Audio (En español)

The period during which symptoms of a disease diminish or disappear.

See Related Term(s): Relapse

Renal Audio (En español)

Pertaining to the kidneys.

Replicate Audio (En español)

To produce a copy or duplicate. The HIV life cycle describes the 7-step process by which HIV replicates.

See Related Term(s): Life Cycle


Also known as: Viral Replication

Replication Cycle

Also known as: Life Cycle

Rescue Therapy

Also known as: Salvage Therapy


Also known as: Latent HIV Reservoir


Also known as: Drug Resistance

Resistance Assay

Also known as: Resistance Testing

Resistance Testing Audio (En español)

Also known as: Resistance Assay

Laboratory testing to identify which, if any, antiretroviral (ARV) drugs will not be effective against a person's specific strain of HIV. Resistance testing is done using a sample of blood. There are two types of resistance testing: genotypic and phenotypic. Resistance testing is used to guide selection of an HIV regimen when initiating or changing antiretroviral therapy (ART).

See Related Term(s): Drug Resistance, Genotypic Antiretroviral Resistance Test, Phenotypic Antiretroviral Resistance Test

Retina Audio (En español)

The light-sensitive membrane that lines the inside of the eye and sends visual messages through the optic nerve to the brain.

Retinal Detachment Audio (En español)

Separation of the retina from its supporting tissue. Retinal detachment must be treated promptly to avoid permanent vision loss. Retinal detachment can be a complication of cytomegalovirus (CMV) retinitis, which is a viral infection that can occur in people with weakened immune systems, including people with HIV.

See Related Term(s): Retina

Retinitis Audio (En español)

Inflammation of the retina.

See Related Term(s): Retina

Retrospective Study Audio (En español)

A type of medical research study. Retrospective studies look back in time to compare a group of people with a particular disease or condition to a group of people who do not have the disease or condition. Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition.

Retrovirus Audio (En español)

A type of virus that uses RNA as its genetic material. After infecting a cell, a retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA. The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. HIV, the virus that causes AIDS, is a retrovirus.

See Related Term(s): Life Cycle

Reverse Transcriptase (RT) Audio (En español)

An enzyme found in HIV (and other retroviruses). HIV uses reverse transcriptase (RT) to convert its RNA into viral DNA, a process called reverse transcription. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) prevent HIV from replicating by blocking RT.

See Related Term(s): Life Cycle, Non-Nucleoside Reverse Transcriptase Inhibitor, Reverse Transcription

Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) Audio (En español)

A type of viral load test. Viral load tests are used to diagnose acute HIV infection, guide treatment choices, and monitor response to antiretroviral therapy (ART).

See Related Term(s): Viral Load Test

Reverse Transcription Audio (En español)

The second of seven steps in the HIV life cycle. During reverse transcription, HIV uses reverse transcriptase (an HIV enzyme) to convert genetic information carried in HIV RNA to make HIV DNA.

See Related Term(s): Life Cycle, Non-Nucleoside Reverse Transcriptase Inhibitor, Nucleoside Reverse Transcriptase Inhibitor, Reverse Transcriptase

Rhabdomyolysis Audio (En español)

Breakdown or death of muscle tissue, often with release of muscle fiber contents into the bloodstream and sometimes leading to acute renal failure. Rhabdomyolysis may be caused by HIV infection, opportunistic infections, or some antiretroviral (ARV) drugs.

Ribonucleic Acid (RNA) Audio (En español)

One of two types of genetic material found in all living cells and many viruses. (The other type of genetic material is DNA.) There are several types of ribonucleic acid (RNA). RNA plays important roles in protein synthesis and other cell activities.

See Related Term(s): Deoxyribonucleic Acid, Messenger RNA

Rigors Audio (En español)

Shivering that is caused by a chill.


Also known as: Ribonucleic Acid

Rod Body Disease

Also known as: Nemaline Rod Myopathy


Also known as: Reverse Transcriptase

Ryan White HIV/AIDS Program Audio (En español)

Also known as: CARE Act

The largest federally funded program providing HIV-related services to low-income, uninsured, and underinsured people with HIV/AIDS. The program's services are available in all 50 states and U.S. territories.

See Related Term(s): Health Resources and Services Administration

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