Intestinal physiology in the parasitized host: integration, disintegration, and reconstruction of systems.

As noted in the introduction, the major objective in discussing gut inflammation in the parasitized host is to underscore the difficulty in establishing whether an inflammation-induced change represents a physiological adaptation or maladaptation (Fig. 3). Deciding whether a specific physiological adjustment, even one that contributes to disease, serves a useful function depends on the perspective of the observer who is in possession of information to make a critical judgment. This is like considering adaptations from an evolutionary sense where the significance of a change that evolved as a consequence of natural selection must be interpreted relative to the long-term "goal directedness" of that change, e.g., relative to its contribution to reproductive fitness. Because of the contributions of inflammation to both symptoms of disease and to the development of functional immunity, the parasitized host provides a means whereby both negative and positive effects of mucosal responses can be studied simultaneously. A careful analysis of the consequences of inflammation is important in contemplating the meaning of "neuroimmunophysiology of gastrointestinal mucosa."