Allergies:

Macrophage: a large inflammatory cell in the body's defense mechanism whose function is to ingest and destroy large particles (damaged or old cells, foreign particles and bacteria).

Major Histocompatibility   Complex (MHC): all of the genes which cover the synthesis of  antigens specific for each individual subject (all the molecules present on the surface of a cell which allow the body's immune system to recognize a cell as belonging to the body or not). It is the biological identification of the subject. It is synonymous for HLA system (Human Leukocyte Antigen).

Mast Cell: an immune cell which secretes chemical substances (mainly histamine) that participate in the body's defense mechanisms. A mast cell is produced in the bone marrow from a stem cell.

Mites: very small organisms (a few millimeters at most in size) which are often parasitic and pathogenic.  A mite is an ectoparasite (a parasite which lives on the skin) from the arachnid family.

Molds: a cryptogrammic plant (microscopic parasitic fungi) which forms a moss with greenish-white or black velvety patches.

Monocyte: "leukocyte" whose nucleus is round and who has only one lobe (mononuclear cell). Monocytes which leave the blood to penetrate into a tissue are converted in "macrophages".

Mucus: a secreted product of the mucus glands or goblet cells (respiratory, digestive, genital) which has a viscous appearance.

Mustard: a plant with yellow flowers cultivated as fodder or green fertilizer and whose black grains are the basis for the commercially prepared condiment which carries the same name