Terms Starting with Letter: I immune system The cells and tissues which are responsible for recognizing and attacking foreign microbes and substances in the body by means of cellular (eg, lymphocytes) and soluble (eg, antibodies) components. immunoglobulin Any protein that functions as an antibody. immunohistochemistry Demonstration of specific antigens in tissues by the use of markers that are either flourescent dyes or enzymes such as horseradish peroxidase. immunosuppression The administration of drugs or other chemicals to prevent the occurrence of an immune reaction. in vitro Latin, literally "in glass." Refers to tests or reactions taking place outside a living organism, on a microscope slide, in a test tube, etc. in vivo Latin meaning "in life." Refers to events that take place within a living organism. inbred mice Genetically identical mice facilitating reproducible animal experiments. induction An increase in the expression of a gene due to the activity of a regulatory protein. interleukins Any of a group of protein factors which are produced by T lymphocytes and macrophages in the presence of antigens or mitogens. They cause the T lymphocytes to activate and proliferate. intravital microscopy Microscopic examination of living organisms (usually mice or rats) by chamber models, confocal or two-photon technologies. iron oxide particles Nanoparticles with high magnetic moment that generate strong local susceptibility and local field inhomogeneities, and thus strong T2 and T2* effects in MR imaging. isotope A chemical element having the same atomic number as another but a different atomic weight. Isotopes that spontaneously decay are called radioisotopes. Radioisotopes are used in medicine for research, diagnosis, and the treatment of disease.