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

IM
See: Intramuscular

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.

IND
See: Investigational New Drug Application

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

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.

Infectious
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