R

RADIOLOGY:
The science of diagnosis and/or treatment using radiant energy. Includes x- rays, CT scan, and destruction of tumors by radiation.

RANDOMIZED TRIAL:
A study in which participants are randomly (i.e., by chance) assigned to one of two or more treatment arms or regimen of a clinical trial. Occasionally placebos are utilized. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms.

REACTOGENICITY:
The capacity to produce adverse reactions.

RECEPTOR:
A molecule on the surface of a cell that serves as a recognition or binding site for antigens, antibodies, or other cellular or immunological components.

RECOMBINANT:
An organism whose genome contains integrated genetic material from a different organism. Also used in relation to compounds produced by laboratory or industrial cultures of genetically engineered living cells (see Genetic Engineering). The cells genes have been altered to give the capability of producing large quantities of the desired compound for use as a medical treatment. Recombinant compounds often are altered versions of naturally occurring substances.

RECOMBINANT DNA:
See Biotechnology; Genetic Engineering.

RECOMBINANT DNA TECHNOLOGY:
See Genetic Engineering.

REFRACTORY:
Referring to a disease that does not readily respond to treatment.

REGULATORY GENES:
As related to HIV: Three regulatory HIV genes -- tat, rev, and nef -- and three so-called auxiliary genes vif, vpr, and vpu -- contain information for the production of proteins that regulate the virus's ability to infect a cell, produce new copies of the virus, or cause disease.

REGULATORY T CELLS:
T cells that direct other immune cells to perform special functions. The chief regulatory cell, the CD4+ T cell or T helper cell, is HIV's chief target.

REMISSIONS:
The lessening of the severity or duration of outbreaks of a disease, or the abatement (diminution in degree or intensity) of symptoms altogether over a period of time.

RENAL:
Pertaining to the kidneys.

RESCRIPTOR:
See Delavirdine.

RESISTANCE:
Reduction in a pathogen's sensitivity to a particular drug. Resistance is thought to result usually from a genetic mutation. In HIV, such mutations can change the structure of viral enzymes and proteins so that an antiviral drug can no longer bind with them as well as it used to. Resistance detected by searching a pathogen's genetic makeup for mutations thought to confer lower susceptibility is called "genotypic resistance." Resistance that is found by successfully growing laboratory cultures of the pathogen in the presence of a drug is called "phenotype resistance."

RETICULOENDOTHELIAL CELLS:
A system of interstitial cells that includes all the phagocytic cells, which trap and consume foreign agents, except the leukocytes circulating in the bloodstream. This system forms a network throughout the body and is another of the body's defense systems against invading organisms in the connective tissues of the body. See Phagocyte.

RETINA:
Light-sensitive tissue at the back of the eye that transmits visual impulses via the optic nerve to the brain. See Retinitis.

RETINAL DETACHMENT:
Condition in which a portion of the retina becomes separated from the inner wall of the eye. In AIDS patients, it can result from retinal disease such as CMV retinitis. The condition can rapidly lead to vision loss but is treatable by adding silicone to the eye's vitreous humor to increase the pressure on the retina.

RETINITIS:
Inflammation of the retina, linked in AIDS to cytomegalovirus (CMV) infection. Untreated, it can lead to blindness.

RETROVIR:
See Zidovudine.

RETROVIRUS:
A type of virus that, when not infecting a cell, stores its genetic information on a single-stranded RNA molecule instead of the more usual double-stranded DNA. HIV is an example of a retrovirus. After a retrovirus penetrates a cell, it constructs a DNA version of its genes using a special enzyme called reverse transcriptase. This DNA then becomes part of the cell's genetic material.

REV:
(rev) One of the regulatory genes of HIV. Three HIV regulatory genes -- tat, rev, and nef -- and three so-called auxiliary genes -- vif, vpr, and vpu -- contain information necessary for the production of proteins that control the virus's ability to infect a cell, produce new copies of the virus, or cause disease.

REVERSE TRANSCRIPTASE:
This enzyme of HIV -- and other retroviruses -- converts the single-stranded viral RNA into DNA, the form in which the cell carries its genes. Some antiviral drugs approved by the FDA for the treatment of HIV infection (e.g., AZT, ddC, ddI, 3TC, D4T, and abacavir) work by interfering with this stage of the viral life cycle. They are also referred to as reverse transcriptase inhibitors (RTIs).

RIBONUCLEIC ACID (RNA):
1. A nucleic acid, found mostly in the cytoplasm -- rather than the nucleus -- of cells, that is important in the synthesis of proteins. The amount of RNA varies from cell to cell. RNA, like the structurally similar DNA, is a chain made up of subunits called nucleotides. In protein synthesis, messenger RNA (see mRNA) replicates the DNA code for a protein and moves to sites in the cell called ribosomes. There, transfer RNA (tRNA) assembles amino acids to form the protein specified by the messenger RNA. Most forms of RNA (including messenger and transfer RNA) consist of a single nucleotide strand, but a few forms of viral RNA that function as carriers of genetic information (instead of DNA) are double-stranded. Some viruses, such as HIV, carry RNA instead of the more usual genetic material DNA. See Cytoplasm; Retrovirus.

RIBOSOME:
A cytoplasmic organelle, composed of ribonucleic acid and protein, that functions in the synthesis of protein. Ribosomes interact with messenger RNA (see mRNA) and transfer RNA to join together amino acid units into a polypeptide chain according to the sequence determined by the genetic code.

RITONAVIR:
A protease inhibitor first approved by FDA in 1996 for use alone or in combination with nucleoside analogs for the treatment of HIV infection in adults and children 2 years of age and older. Also called Norvir.

RNA:
See Ribonucleic Acid.

ROUTE OF ADMINISTRATION:
See Administration.

RTI:
(Reverse Transcriptase Inhibitors). See Reverse Transcriptase.

RT-PCR:
(Reverse Transcriptase Polymerase Chain Reaction). An FDA-approved test to measure viral load. The test is also known as PCR (see Polymerase Chain Reaction).

RYAN WHITE C.A.R.E. ACT:
Through the Ryan White Comprehensive AIDS Resources Emergency (C.A.R.E.) Act, health care and support services are provided for persons living with HIV/AIDS. HRSA administers this Act, which was reauthorized by Congress in 1996 for 5 years. The metropolitan areas most affected by the HIV epidemic are awarded Title I grants to improve and expand health care. Title II grants to states and territories support essential health care and support services for persons living with HIV/AIDS, including health insurance and AIDS Drug Assistance Programs. Title III(b) supports early intervention in clinical settings such as community and migrant health centers, health care for the homeless programs, and Native Hawaiian health programs. Title IV supports services for women, children, adolescents, and families affected by the HIV epidemic. Part F of the Act supports Special Projects of National Significance (SPNS) and AIDS Education and Training Centers (AETCs).