Malaria is caused by one-cell animals of the genus Plasmodium. The patients suffer from chills and attacks of fever. The disease is especially prevalent in humid, tropical areas. Plasmodia are transmitted by the bite of the anopheles mosquito.

Mammography: X-ray examination of the breast.

Mastocytes are large cells which are distributed in connective tissue throughout the entire body. They contain large granulomas in which a wide range of intermediary molecules such as histamine are stored. Mastocytes possess high affinity Fce receptors (FceRI) which enable them to bind IgE molecules. The binding of antigens to these IgE molecules triggers the activation of the mastocytes which release the intermediary molecules from their granulomas. This leads to an immediate local or systemic hypersensitivity reaction. Mastocytes play an important role in allergic reactions.

Mature B cells are cells which bear IgM and IgD on their surface and can react to antigens.

Memory cells: Following infection by a pathogen, T and B memory cells form which rapidly become active in the event of a renewed infection with the same pathogen. The immune defence is prepared and can prevent the excessive spread of viruses or bacteria.

Messenger substances: Substances acting as signals, used by the cells to communicate with one another.

Metastases: Tumour cells which break off from the primary tumour and form subsidiary tumours.

MHC (major histocompatibility complex) is a group of genes which determines the structure of MHC molecules. All of the body's cells bear MHC-I molecules on their surface. In a manner of speaking, the MHC molecules serve as identification papers. They vary from one individual to the next and help the immune system to distinguish between own and foreign. MHC-II molecules appear only on cells which are presenting antigens.

MHC molecules have a kind of depression in which the antigen, or parts thereof, is presented as if on a display platter. This is the way other cells of the immune system become aware of the pathogen and can initiate appropriate defence actions.

MHC-I molecule: Docking station of cytotoxic T cells with the receptor CD8. Microorganisms are microscopically small organisms and are, with the exception of some fungi, one-cell. They include bacteria, yeasts and other fungi and protozoa. Many of them can cause diseases in human beings.

Microorganisms are microscopically small organisms and are, with the exception of some fungi, one-cell. They include bacteria, yeasts and other fungi and protozoa. Many of them can cause diseases in human beings.

Monoclonal antibodies are antibodies which are produced by a single B cell clone. They are normally produced by creating hybrid antibody-forming cells from the fusion of myeloid cells and immune spleen cells.

Monocytes are white blood cells with a bean-shaped nucleus. They are the precursor cells of the macrophages.

Monokines are cytokines released by macrophages.

Multiple sclerosis is a neurological disease characterized by the loss of myelin sheaths in the central nervous system, the appearance of lymphocytes in the brain and a chronic progressive course. It is believed to be an autoimmune disease.

Mutation: As part of cell division, the genetic information is doubled and distributed among the daughter cells. During this process, errors can occur which are called mutation.

Myasthenia gravis is an autoimmune disease in which autoantibodies against the acetylcholine receptors on skeletal muscle cells block the signal transmission to neuromuscular synapses. This disease leads to a fatigue paralysis which gradually gains in intensity and ultimately to death.