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• AIDS HIV Terms

AIDS-HIV Related Terms

- M -

• MAC

See Mycobacterium Avium Complex.



• Macrophage

A large immune cell that devours invading pathogens and other intruders. Stimulates other immune cells by presenting them with small pieces of the invader. Macrophages can harbor large quantities of HIV without being killed, acting as reservoirs of the virus.



• Macrophage-Tropic Virus

HIV strains that preferentially infect macrophages in cell culture experiments. They readily fuse with cells that have both CD4 and CCR5 molecules on their surfaces, whereas the same viral isolates fail to fuse with cells expressing only CD4. These isolates are the main strains found in patients during the symptom-free stage of HIV disease.



• Magnetic Resonance Imaging (MRI)

A noninvasive, non-x-ray diagnostic technique that provides computer-generated images of the body's internal tissues and organs.



• MAI

See Mycobacterium Avium Complex.



• Maintenance Therapy

Also referred to as secondary prophylaxis. A therapy that prevents reoccurrence of an infection that has been brought under control.



• Major Histocompatibility Complex (MHC)

Two classes of molecules on cell surfaces. MHC class I molecules exist on all cells, and hold and present foreign antigens to CD8 cytotoxic T lymphocytes if the cell is infected by a virus or other microbe. MHC class II molecules are the billboards of the immune system. Peptides derived from foreign proteins are inserted into MHC's binding groove and displayed on the surface of antigen-presenting cells. These peptides are then recognized by T lymphocytes so that the immune system is alerted to the presence of foreign material. See Histocompatibility Testing.



• Malabsorption Syndrome

Decreased intestinal absorption resulting in loss of appetite, muscle pain, and weight loss. See AIDS Wasting Syndrome.



• Malaise

A generalized, nonspecific feeling of discomfort.



• Malignant

Refers to cells or tumors growing in an uncontrolled fashion. Such growths may spread to and disrupt nearby normal tissue, or reach distant sites via the bloodstream. By definition, cancers are always malignant, and the term 'malignancy' implies cancer. See Metastasis.



• Mast Cell

A granulocyte found in tissue. The contents of the mast cells, along with those of basophils, are responsible for the symptoms of allergy.



• Medlineplus

Contains extensive information from the National Institutes of Health and other trusted sources on about 500 diseases and conditions. There are also lists of hospitals and physicians, a medical encyclopedia and dictionaries, health information in Spanish, extensive information on prescription and nonprescription drugs, health information from the media, and links to thousands of clinical trials. Internet address



• Mega-Haart

Also referred to as multi-drug rescue therapy. Salvage or rescue regimens containing 6 or more antiretroviral drugs for patients who have had previous treatment. The hypothesis is that patients with multiple drugs exposure and failures are unlikely to be infected with virus that is resistant to all drugs in the rescue regimen.



• Memory T Cells

A subset of T lymphocytes that have been exposed to specific antigens and can then proliferate (i.e., reproduce) on subsequent immune system encounters with the same antigen.



• Meninges

Membranes surrounding the brain or spinal cord. Part of the so-called 'blood-brain barrier.' See Meningitis.



• Meningitis

An inflammation of the meninges (membranes surrounding the brain or spinal cord), which may be caused by a bacterium, fungus, or virus. See Cryptococcal Meningitis; Central Nervous System.



• Messenger Rna

Also referred to as mRNA. An RNA (ribonucleic acid) that carries the genetic code for a particular protein from the DNA in the cell's nucleus to a ribosome in the cytoplasm and acts as a template, or pattern, for the formation of that protein.



• Metabolism

The chemical changes in living cells by which energy is provided for vital processes and activities and new material is assimilated.



• Metastasis

The spread of a disease (e.g., cancer) from an original site to other sites in the body.



• MHC

See Major Histocompatibility Complex.



• Microbes

Microscopic living organisms, including bacteria, protozoa, viruses, and fungi.



• Microbicide

An agent (e.g., a chemical or antibiotic) that destroys microbes. Research is being carried out to evaluate the use of rectal and vaginal microbicides to inhibit the transmission of sexually transmitted diseases, including HIV.



• Microsporidiosis

An intestinal infection that causes diarrhea and wasting in persons with HIV. It results from two different species of microsporidia, a protozoal parasite. In HIV infection, it generally occurs when CD4+ T cell counts fall below 100. See Pathogen; Protozoa; AIDS Wasting Syndrome.



• Mitochondria

Organelles (particles of a living substance) within the cytoplasm of the cells, that serve as a source of energy for the cell.



• Mitochondrial Toxicity

Also referred to as mitochondrial dysfunction. A possible side effect of certain anti-HIV drugs, primarily NRTIs, that results in mitochondrial damage. This damage can cause symptoms in the heart, nerves, muscles, pancreas, kidney, and liver, and it can also cause changes in lab tests. Some of the common conditions related to mitochondrial toxicity include myopathy, peripheral neuropathy, pancreatitis, thrombocytopenia, anemia, and neutropenia. Mitochondrial damage can lead to lactic acidosis and hepatitic steatosis ('fatty liver'). It also may play a role in lipodystrophy.



• Molecule

The smallest particle of a compound that has all the chemical properties of that compound. Molecules are made up of two or more atoms, either of the same element or of two or more different elements.



• Molluscum Contagiosum

A disease of the skin and mucous membranes caused by a poxvirus (molluscum contagiosum virus, MCV) infection. It is characterized by pearly white or flesh-colored papules (bumps) on the face, neck, and genital region. In persons living with HIV, molluscum contagiosum is often a progressive disease, resistant to treatment. When CD4+ cells fall below 200, the lesions tend to proliferate and spread.



• Monocyte

A large white blood cell that ingests microbes or other cells and foreign particles. When a monocyte enters tissues, it develops into a macrophage.



• Mononeuritis Multiplex (MM)

A rare type of neuropathy that has been described with HIV infection. It may fall into two different settings. One type occurs during the early period of the infection and has a more benign outcome. The second form occurs later and is more aggressive, leading to progressive paralysis and death in some patients. It has been suggested that MM is related to multifocal cytomegalovirus (CMV) infection.



• Monovalent Vaccine

A vaccine that is specific for only one antigen.



• Morbidity

The condition of being diseased or sick; also the incidence of disease or rate of sickness.



• MRI

See Magnetic Resonance Imaging.



• Mucocutaneous

Anything that concerns or pertains to mucous membranes and the skin (e.g., mouth, eyes, vagina, lips, or anal area).



• Mucosa

See Mucous Membrane.



• Mucosal Immunity

Resistance to infection across the mucous membranes. Dependent on immune cells and antibodies present in the lining of the urogenital tract, gastrointestinal tract, and other parts of the body exposed to the outside world.



• Mucous Membrane

Moist layer of tissue lining the digestive, respiratory, urinary, and reproductive tracts-all the body cavities with openings to the outside world except the ears.



• Multi-Drug Rescue Therapy

See Mega-HAART.



• Multiple Drug-Resistant Tuberculosis (MDR-TB)

A strain of TB that does not respond to two or more standard anti-TB drugs. MDR-TB usually occurs when treatment is interrupted, thus allowing organisms in which mutations for drug resistance have occurred to proliferate. See Tuberculosis.



• Mutation

During the course of HIV disease, mutated HIV strains may emerge in an infected individual. These mutated strains may differ widely in their ability to infect and kill different cell types, as well as in their rate of replication. Of course, HIV does not mutate into another type of virus.



• Myalgia

Diffuse muscle pain or tenderness, usually accompanied by malaise (vague feeling of discomfort or weakness).



• Mycobacterium

Any bacterium of the genus Mycobacterium or a closely related genus.



• Mycobacterium Avium Complex (MAC)

1. A common opportunistic infection caused by two very similar mycobacterial organisms, Mycobacterium avium and Mycobacterium intracellulare (MAI), found in soil and dust particles. 2. A bacterial infection that can be localized (limited to a specific organ or area of the body) or disseminated throughout the body. It is a life-threatening disease, although new therapies offer promise for both prevention and treatment. MAC disease is extremely rare in persons who are not infected with HIV. It generally occurs when the CD4+ T cell count falls below 50.



• Mycosis

Any disease caused by a fungus.



• Myelin

A substance that sheathes nerve cells, acting as an electric insulator that facilitates the conduction of nerve impulses. See Chronic Idiopathic Demyelinating Polyneuropathy.



• Myelopathy

Any disease of the spinal cord.



• Myelosuppression

Suppression of bone marrow activity, causing decreased production of red blood cells (anemia), white blood cells (leukopenia), or platelets (thrombocytopenia). Myelosuppression is a side effect of some drugs, such as AZT.



• Myelotoxic

Destructive to bone marrow.



• Myocardial

Refers to the heart's muscle mass.



• Myopathy

Progressive muscle weakness. Myopathy may arise as a toxic reaction to AZT or as a consequence of the HIV infection itself.