SEROCONVERSION: The development of antibodies to a particular antigen. When people develop antibodies to HIV or an experimental HIV vaccine, they "seroconvert" from antibody-negative to antibody-positive. See also Antibodies; Antigen.

SEROPREVALENCE: As related to HIV infection: The proportion of persons who have serologic (i.e., pertaining to serum) evidence of HIV infection at any given time. See also Serum.

SEROSTATUS: Results of a test for specific antibodies. See also Antibodies.

SERUM: The clear, thin and sticky fluid portion of the blood that remains after coagulation. Serum contains no blood cells, platelets or fibrinogen.

SEXUALLY TRANSMITTED DISEASE (STD): Also called venereal disease. A contagious disease usually acquired by sexual intercourse or genital contact. Historically, the five venereal diseases were: gonorrhea, syphilis, chancroid, granuloma inguinale and lymphogranuloma venereum. To these have been added scabies, herpes genitalis and anorectal herpes and warts, pediculosis, trichomoniasis, genital candidiasis, molluscum contagiosum, nonspecific urethritis, chlamydial infections, cytomegalovirus and AIDS. See also Herpes Simplex Virus II; Molluscum Contagiosum.

SF-2: A strain of HIV used in vaccine development.

SHINGLES: See Herpes Varicella Zoster Virus.

SHIV: Genetically engineered hybrid virus having an HIV envelope and an SIV core. See also Genetic Engineering; Hybrid; Simian Immunodeficiency Virus.

SIDE EFFECTS: The action or effect of a drug (or vaccine) other than that desired. The term usually refers to undesired or negative effects, such as headache, skin irritation or liver damage. Experimental drugs must be evaluated for both immediate and long-term side effects.

SIMIAN IMMUNODEFICIENCY VIRUS (SIV): An HIV-like virus that infects monkeys, chimpanzees and other nonhuman primates.

SIV: See Simian Immunodeficiency Virus.

STANDARDS OF CARE: Treatment regimen or medical management based on state-of-the-art patient care.

STATISTICAL SIGNIFICANCE: A term based on statistical tests that is used to denote the probability that the observed association could have occurred by chance alone. Does not refer to medical or biological significance of an association. For example, a statistical significance at the 1-percent level indicates a 1-in-100 chance that a result can be ascribed to chance.

STD: See Sexually Transmitted Disease.

STEM CELLS: Cells from which all blood cells derive. Bone marrow is rich in stem cells.

STERILIZING IMMUNITY: An immune response that completely eliminates an infection.

SUBCLINICAL INFECTION: An infection, or phase of infection, without readily apparent symptoms or signs of disease.

SUBCUTANEOUS: Beneath or introduced beneath the skin (e.g., subcutaneous injections).

SUBUNIT HIV VACCINE: A genetically engineered vaccine that is based on only part of the HIV molecule. See also Genetic Engineering.

SUPERANTIGEN: Investigators have proposed that a molecule known as a superantigen, either made by HIV or an unrelated agent, may stimulate massive quantities of CD4+ T cells at once, rendering them highly susceptible to HIV infection and subsequent cell death. See also Antigen; CD4 (T4) or CD4+ Cells.

SUPPRESSOR T CELLS: (T8, CD8). Subset of T cells that halt antibody production and other immune responses. See also Antibodies; T Cells.

SURROGATE MARKER: A substitute; a person or thing that replaces another. In HIV disease, the number of CD4+ T cells and CD8+ cells is a surrogate immunological marker of disease progression. See also CD4 (T4) or CD4+ Cells; CD8 (T8) Cells.

SURVEILLANCE: Close or continuous observation or testing (e.g., serosurveillance), used, among others, in epidemiology. Immunological surveillance, or immunosurveillance, is a monitoring process of the immune system that detects and destroys neoplastic (e.g., cancerous) cells and that tends to break down in immunosuppressed individuals. See also Epidemiologic Surveillance.

SYMPTOMS: Any perceptible, subjective change in the body or its functions that indicates disease or phases of disease, as reported by the patient.

SYNDROME: A group of symptoms and diseases that together are characteristic of a specific condition.

SYNERGISM/SYNERGISTIC: An interaction between two or more agents (drugs) that produces or enhances an effect that is greater than the sum of the effects produced by the individual agents.