Glossary of terms

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• Idiopathic
• Without a known cause.
• Idiopathic Thrombocytopenia Purpura (ITP)
• A rare autoimmune disorder characterized by a shortage of platelets in the blood, which results in bruising and spontaneous bleeding. See also: Platelets.
• IFN
• See: Interferon.
• IG
• See: Immunoglobulin.
• IHS
• See: Indian Health Service.
• IL-2
• See: Interleukin-2.
• IL-7
• See: Interleukin-7.
• Immune Complex
• Term used to describe an antibody bound to an antigen. See also: Antibody, Antigen.
• Immune Reconstitution Syndrome (IRS)
• Also known as immune restoration disease (IRD) or immune reconstitution inflammatory syndrome (IRIS). An inflammatory reaction that can occur when an immunocompromised person's immune system improves, such as when a person with HIV disease begins anti-HIV treatment and experiences a rise in CD4 cell count. Fever, along with swelling, redness, or discharge at the site of an injury or infection, may signal that an infection previously unnoticed by a weak immune system is now a target of a stronger immune system. Although IRS indicates that a person's immune system has grown healthier, it can be a serious, sometimes fatal condition and must be treated aggressively.
• Immune Response
• The body's defensive reaction to a foreign invader, such as a virus, bacteria, or fungus. The immune response includes both humoral (antibody-based) and cell-mediated immunity. See also: Cell-Mediated Immunity, Humoral Immunity.
• Immune System
• The collection of cells and organs whose role is to protect the body from foreign invaders. Includes the thymus, spleen, lymph nodes, B and T cells, and antigen-presenting cells.
• Immunity
• Protection against or resistance to disease.
• Immunization
• See: Vaccination.
• Immunocompetent
• Able to mount a normal immune response.
• Immunocompromised
• Unable to mount a normal immune response because of an impaired immune system.
• Immunodeficiency
• Inability to produce normal amounts of antibodies, immune cells, or both.
• Immunogenicity
• The ability of an antigen or vaccine to stimulate an immune response. See also: Antigen, Vaccine.
• Immunoglobulin (IG)
• See: Antibody.
• Immunologic Failure
• An HIV-infected individual is said to be experiencing immunologic failure if the individual's CD4 count decreases below his or her baseline count or does not increase above the baseline count within the first year of anti-HIV treatment. People with virologic failure who do not switch to an effective drug regimen usually progress to immunologic failure within about 3 years. Immunologic failure may be followed by clinical failure. See also: Baseline, Virologic Failure, Clinical Failure.
• Immunomodulator
• A natural or man-made substance that can modify the functioning of the immune system.
• Immunosuppression
• Inability of the immune system to function normally. May be caused by drugs (for example, chemotherapy), or result from certain diseases (for example, HIV infection).
• Immunotherapy
• Treatment to stimulate or restore the body's immune system to fight disease.
• In Vitro
• Latin for "in glass." A term meaning that a research study was conducted in an artificial environment created outside a living organism (for example, in a test tube or petri dish).
• In Vivo
• Latin for "in life." A term meaning that a research study was conducted in a living organism (animal or human).
• Incidence
• The rate of occurrence of new cases of a particular disease in a given population. Often reported as number of cases per 100,000 people.
• Inclusion/Exclusion Criteria
• A specific set of selection rules that determine whether a person is eligible to enroll in a particular clinical trial. For example, some trials may not accept people with chronic liver disease or with certain drug allergies. Others may exclude men or women, or only include people with a certain CD4 count or viral load. See also: Clinical Trial.
• Incubation Period
• The period between infection with a micro-organism and the development of symptoms. See also: Window Period.
• IND
• See: Investigational New Drug Application.
• Indian Health Service (IHS)
• The agency within the U.S. Department of Health and Human Services (DHHS) responsible for providing Federal health services to American Indians and Alaska Natives.
• Infection
• Establishment of an infectious micro-organism in a suitable host. The term is also used to refer to disease caused by an infectious micro-organism.
• Capable of causing infection.
• Informed Consent
• A person's agreement to participate in a clinical trial after understanding all aspects of the trial, including potential risks and benefits. See also: Clinical Trial.
• Infusion
• Administration of a solution (such as a glucose or salt solution), usually into a vein.
• Inoculation
• See: Vaccine.
• Institutional Review Board (IRB)
• A committee of experts who review and monitor clinical trials to ensure that they are ethical and that the rights of study participants are protected. Federal regulations dictate that any institution that conducts or supports clinical trials must have an IRB.
• Insulin Resistance
• An abnormal body response to insulin, a hormone that regulates glucose (sugar) levels. People with insulin resistance have abnormally high blood levels of insulin, which may lead to heart and cholesterol problems and obesity. Insulin resistance may occur in HIV-infected individuals taking certain PIs.
• Integrase
• An HIV protein that plays an important role in the virus's life cycle. Integrase inserts HIV's genetic information into the infected cell's own DNA. See also: Integration.
• Integrase Inhibitors
• A class of anti-HIV drugs that prevents the HIV integrase protein from inserting HIV's genetic information into an infected cell's own DNA. See also: Integrase.
• Integration
• The process by which HIV integrase inserts HIV's genetic material into an infected cell's own DNA. This crucial step in HIV's life cycle is targeted by the class of anti-HIV drugs called integrase inhibitors. See also: Integrase, Integrase Inhibitors.
• Intensification
• Adding additional anti-HIV drugs to an existing treatment regimen, usually because that regimen failed to adequately control HIV replication.
• Interaction
• See: Drug Interaction.
• Interferon (IFN)
• A cytokine (protein that regulates immune system activity) that the body produces to fight viruses. Laboratory-made versions of IFN are used in the treatment of some virus infections and cancers. There are three main types of interferon: alpha, beta, and gamma. IFN alpha is used to treat hepatitis C virus (HCV) infection and many cancers, including Kaposi's sarcoma. See also: Cytokines, Hepatitis C Virus, Kaposi's Sarcoma.
• Interleukin-2 (IL-2)
• A cytokine (protein that regulates immune system activity) that can increase the production of certain disease-fighting white blood cells. During HIV infection, IL-2 levels gradually decline. A laboratory-made version of IL-2 is used to treat some cancers and has been studied as a way to increase the number of CD4 cells and other immune system cells in people with HIV.
• Interleukin-7 (IL-7)
• A substance produced in small amounts in bone marrow cells that increases the body's production of certain disease-fighting white blood cells. Laboratory-produced IL-7 is a drug product that appears to induce HIV replication in latent, or resting, infected cells. Activation of HIV in resting cells allows antiretroviral drugs to target HIV in those cells.
• Interstitial Nephritis
• A kidney disorder caused by inflammation of the small spaces between parts of the kidney. The condition is a potential side effect of certain anti-HIV drugs.
• Intramuscular (IM)
• Relating to the area within a muscle. Intramuscular also refers to an injection made directly into a muscle.
• Intrapartum
• The time period spanning labor and delivery.
• Intravaginal
• Within the vagina.
• Intravenous
• Inside a vein. Intravenous also refers to an injection made directly into a vein.
• Intravenous Immunoglobulin (IVIG)
• A solution of antibodies taken from healthy donors and injected into the veins of people with low or abnormal antibody production to help protect them from infections. See also: Antibody.
• Investigational Drug
• Also known as experimental drug. A drug that has not been approved by the FDA to treat a particular disease or condition. The safety and effectiveness of an investigational drug must be tested in clinical trials before the manufacturer can request FDA approval for a specific use of the drug. See also: Clinical Trial, Investigational New Drug Application.
• Investigational New Drug Application (IND)
• The process through which data about an experimental drug is submitted to and reviewed by the Food and Drug Administration (FDA) before the drug is allowed to be tested in clinical trials. See also: Clinical Trial, New Drug Application.
• IRB
• See: Institutional Review Board.
• IRS
• See: Immune Reconstitution Syndrome.
• Isosporiasis
• An infection caused by the protozoan Isospora belli, which enters the body through contaminated food or water. Symptoms include diarrhea, fever, headache, abdominal pain, vomiting, and weight loss. Isosporiasis is considered an AIDS-defining condition in people with HIV.
• ITP
• See: Idiopathic Thrombocytopenia Purpura.
• IVIG
• See: Intravenous Immunoglobulin.