Cross-tolerance

Cross tolerace refers to a pharmacologicalphenomenon, in which a patient being treated with a drug exhibits a physiological resistance to that medication as a result of tolerance to a pharmacologically similar drug. It is observed in treatment with antivirals, antibiotics, analgesics and many other medications.

Cross-tolerance is particularily frequent amongst users of illicit drugs. For example, users with a high tolerance to the stimulant amphetaminewill may also exhibit a high tolerance to the structurally similar methamphetamineor other amphetamine-like stimulants, such as methylphenidate(though one should not assume this to avoid overdose). The phenomenon is also observed in cigarrettesmokers, in whom there is a demonstrably lessened sensitivity to the effects of caffeine. Cross-tolerance is also frequent in response to use of hallucinogens. General tolerance to the effects of tryptaminessuch as psilocybin, may be dramatic in response to repeated use, and this often translates into a tolerance to effects of other drugs such as LSDor DMT.

Dendritic cellscan take up self antigens from other cells and cross-presentthem to autoreactive T cells. These are then eliminated from the T cell repertoir by apoptosis. This mechanism was proposed to silence autoreactive T cells that have escaped negative selection in the thymus.

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It uses material from the http://en.wikipedia.org/wiki/Cross-tolerance Wikipedia article Cross-tolerance.