Genetic response, modifiers

The role of an immune response to intestinal bacteria in the development of UC may not be as strong a contributing factor as it is in CD. The potential role of environmental factors in the development of UC implies that the immune response is directed against an unknown antigen. The findings that development and severity of UC are reduced in patients who smoke, or in those with appendectomies, may support the theory that these factors may somehow modify either the genetic component or phenotypic response to immunologic stimuli.11,13... 

We have already noted evidence for genetic factors that underlie the preference for and response to caffeine. These factors create a biologically based set of individual difference dimensions that may be modified by experience with the drug. In addition, there is evidence for a number of broader individual difference dimensions that appear to be relevant. These bipolar continua differentiate between subjects who are habitually high in arousal or arousability and those who are habitually low. The factors in question are personality dimensions that theoretically reflect underlying biological continua of arousal or arousability.238 Included among these dimensions are extraversion,58 impulsivity,239240 and sensation-seek-ing.94-241-242 We will take up the first two of these. 

Studies with a variety of genetically modified mice have shed new light on the complex relationship between the protective and pathological immune responses controlling parasite infections. TNF and NO are important components of the pathological response accompanying the expulsion of a gastrointestinal nematode parasite. In the absence of TNF-R1 or iNOS, mice do not develop the severe villus atrophy and mucosal mastocytosis that usually accompany infection with T. spiralis, but their ability to expel the... 

Nicotine has a wide range of effects on behavior in humans and individual response to nicotine may predict predisposition to addiction. Some individuals may be genetically more likely to be hypersensitive to nicotine and, therefore, find it aversive others may be more positively reinforced by nicotine and seek to repeat the stimulus. Genetically modified animals are increasingly important tools for elucidating the molecular mechanisms involved in addiction. 

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