IgE antibodies: Y-shaped antibodies which play a role especially in allergic reactions and in fending off parasites.

Immune complexes result from the binding of antibodies to antigens. If there are enough antibody molecules, then relatively large immune complexes result. They are quickly eliminated by cells with Fc and complement receptors. If there is an excess of antigens, small, soluble immune complexes form which are deposited in small blood vessels, where they can cause damage (antigen-antibody complexes).

Immune monitoring: According to one theory, most incipient tumours are destroyed by lymphocytes which recognize specific tumour antigens as part of the so-called immune monitoring. To be sure, there is hardly any evidence that such a process actually takes place in the body with any notable efficiency. However, the theory is still an important concept in tumour immunology.

Immune response is the reaction of a host to fight off a pathogen. Changes in the blood in the early phase of an infectious disease are called the immune response of the acute phase. This includes the production of proteins of the acute phase and of cellular elements.

Immune system: The immune system includes all tissue, cells and molecules which contribute to acquired immunity. Often the term is extended to include the totality of the defence mechanisms of a host organism.

Immunity is the ability to resist an infection.

Immunization is a procedure for triggering an acquired immune reaction by deliberately causing contact with antigens (active immunization, passive immunization).

Immunobiology refers to research of the biological mechanisms which serve to defend against infectious organisms.

Immunogenetics: The term immunogenetics refers generally to the genetic analysis of molecules which play a role in immunity.

Immunodeficiency diseases are hereditary or acquired illnesses in which one or more components of the immune defence are either lacking or not fully functional.

Immunoglobulins is the general term for antibodies. The specific antigen receptors on B lymphocytes are surface immunoglobulins. Ig is the usual abbreviation for immunoglobulin. The various isotypes of immunoglobulin are IgM, IgD, IgG, IgA and IgE.

Immunological memory: The immunological memory enables a faster and more effective acquired immune response whenever the body has already had contact with the antigen. The immunological memory is specific and long-term.

Immunology is the study of all aspects of defence against infectious organisms and the damaging effects of the immune response.

Immunosuppressives are substances which suppress the acquired immune responses. They are used above all in the treatment of transplant rejection reactions and serious autoimmune diseases.

Infectious mononucleosis, also called Pfeiffer's glandular fever, is caused by an infection of the B cells by the Epstein-Barr virus. The virus stimulates the B cells and they trigger a T cell response, which then controls the infection.

Inflammation is the general term for a localized collection of fluids, plasma proteins and white blood cells resulting from injuries, infections or a localized immune reaction. Acute inflammation refers to early and frequently temporary reactions, while a chronic inflammation means that the infection lasts for a long time or there is an autoimmune reaction. Many different types of inflammation can be observed in various illnesses. Cells which invade tissue and cause inflammation are often called inflammatory cells.

Inflammatory CD4 T cells, also called THI cells (or inflammation T cells), are armed effector T cells which form the cytokines interferon- and tumour necrosis factor upon contact with their antigen. Their most important function is the activation of the macrophages. Some THI cells are also cytotoxically active.

Influenza: True influenza is transmitted by droplet infection. Consequently, the virus can spread rapidly, and epidemics occur frequently. Since influenza viruses modify their shells from time to time, the corresponding vaccine must be prepared in advance each time.

Insulin-dependent diabetes mellitus is a disease in which the beta cells in the isles of Langerhans of the pancreas have been destroyed and insulin can no longer be produced. It is assumed that the disease is a result of an autoimmune reaction to beta cells.

Interferons are cytokines which can cause cells to become resistant to virus attack. Interferon- and Interferon-ß are produced by leukocytes, fibroblasts or others. Interferon- , on the other hand, is a product of inflammatory CD4 T cells, CD8 T cells and natural killer cells. The most important task of Interferon- is the activation of the macrophages.

Interleukin (IL) is the general designation for cytokines produced by leukocytes.

Isotypes: There are five different isotypes, or classes, of immunoglobulins: IgM, IgG, IgD, IgA and IgE. The constant regions of their heavy chains differ from one another and are coded by different genes. The isotype of an antibody determines what effector functions it can exercise when binding to an antigen.