Immune system definitions

The US-EPA OPPTS test guideline on immunotoxicity (OPPTS 870.7800) provides the following definition Immunotoxicity refers to the ability of a test substance to suppress immune responses that could enhance the risk of infectious or neoplastic disease, or to induce inappropriate stimulation of the immune system, thus contributing to allergic or autoimmune disease. ... 

Antilymphocyte antibody acts primarily on the small, long-lived peripheral lymphocytes that circulate between the blood and lymph. With continued administration, "thymus-dependent" lymphocytes from lymphoid follicles are also depleted, as they normally participate in the recirculating pool. As a result of the destruction or inactivation of T cells, an impairment of delayed hypersensitivity and cellular immunity occurs while humoral antibody formation remains relatively intact. ALG and ATG are useful for suppressing certain major compartments (ie, T cells) of the immune system and play a definite role in the management of solid organ and bone marrow transplantation. 

Most of the lysosomal proteases called cathepsins are small 20- to 40-kDa glycoproteins found in all animal tissues.313 Most are cysteine proteases which function best and are most stable in the low pH reducing environment of lysosomes. They resemble papain in size, amino acid sequence, and active site structures. Papain is nonspecific but most cathepsins have definite substrate preferences. Cathepsin B is the most abundant. There are smaller amounts of related cathepsins H (an aminopeptidase)314 and L315 and still less of cathepsins C, K, and others. Cathepsin B is both an endopep-tidase and an exopeptidase.316 It acts on peptides with arginine at either Pj or P2 but also accepts bulky hydro-phobic residues in Pj and prefers tyrosine at P3.317 Cathepsin S is less stable at higher pH than other cathepsins and has a more limited tissue distribution, being especially active in the immune system.318 319... 

Apart from being complex, the human immune system also changes during the body s growth and development. The defense mechanisms involved in building immunity are equally complex. Thus, it is extremely difficult to formulate definite statements on the effect of particular environmental components on the immunological tolerance of a human body, including the impact of diet on the immune system. Until now, the research on human nutrition has focused primarily on the effect of... 

In its most elemental definition, a disease occurs when something in the body malfunctions. Heart attack The walls of a coronary artery become too clogged with fatty deposits, blocking the flow of blood to the heart. Cancer A mutated cell replicates out of control. Infection A virus overcomes the body s immune system. To get the body back to normal, scientists try to find a molecule that will intercept the malfunction. If the disease is caused by the behavior of an enzyme, the molecule could block the enzyme, modify its behavior, or block the receptor it attaches to. In pharmaceutical talk, that magic molecule has been known as a compound. To the public, it s a drug. 

In humans the major and consistent effect is on the skin. Exposed people suffer from a severe form of acne, known as chloracne, after exposure to dioxin. Changes in the immune system have also been detected in the children exposed at Seveso in Italy and workers exposed at the Coalite plant in the UK. The latter had reduced levels of some immunoglobulins. There is no definitive evidence as to whether humans are more or less sensitive to dioxin than other mammals but the weight of evidence would suggest that they are less sensitive than many. 

It proved difficult to definitively demonstrate CRH synthesis from immune cells, although numerous studies provided evidence this does happen (Aird et al., 1993 Ekman et al., 1993). Eventually it became clear that regulation of CRH synthesis and release in immune cells differs from that in hypothalamic neurons. While immune cells may synthesize and release much smaller concentrations of CRH and other neuroimmune peptides, and although their release may require de novo synthesis, an inherently slow process, the fact that immune cells release these hormones locally in the target area compensates for both of these factors to some extent. These data indicating site and tissue specific effects of CRH, sometimes even contradictory effects, point to the complex interrelationship betw een the nervous, endocrine and immune systems, an interaction that has yet to be deciphered completely. 

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