susceptibility to EAE (Mason, 1991). Similar correlations between HPA axis hyporeactivity and susceptibility to autoimmune disease have been observed for autoimmune conditions in chickens (Wick et al., 1998) and mice (Lechner et al., 1996).
Complementing these animal studies, a series of elegantly conducted clinical studies (Torpy and Chrousos, 1996; Buske-Kirschbaum and Hellhammer, 2003) have shown that patients with atopic dermatitis (Buske-Kirschbaum et al., 1997; Buske-Kirschbaum et al., 1998; Buske-Kirschbaum et al., 2001) and asthma (Buske-Kirschbaum et al., 2003) show decreased HPA axis reactivity. Studies of pediatric rheumatic diseases suggest a similar HPA axis deficiency coupled with other proinflammatory hormonal biases (Chikanza et al., 2000). Differences in NK cell stress reactivity and beta(2)-adrenoreceptor upregulation on peripheral blood mononuclear cells have been observed in patients with systemic lupus erythematosus (Pawlak et al., 1999). A more complex role for sympathetic nervous system involvement in autoimmune disease also has been proposed (Kuis et al., 1996; Kavelaars et al., 1998).
Epidemiologic studies have repeatedly linked low social status with increased disease risk and mortality rates (Adler et al., 1994; Adler and Ostrove, 1999). Sapolsky has proposed that the magnitude of chronic stress experienced by individuals of different ranks within a social hierarchy depends on the individual’s personality as well as on the characteristics of social organization, such as dominance style, stability of ranks, availability of coping mechanisms, and ease of avoidance (for review see Sapolsky, 2005). Thus, despotic, top-down hierarchies maintained through aggression are more stressful for dominant animals, while those maintained through psychological intimidation are more stressful for subordinate animals (Sapolsky, 2005). Egalitarian, bottom-up hierarchies in which dominance is obtained through support from subordinate individuals are less stressful for all members. Unstable hierarchies are more stressful for dominant animals, while stable hierarchies can be more stressful for subordinate animals that have less access to food and mates. Societies that have a high availability of coping outlets (grooming, physical contact, coalition formation) are less stressful for all individuals, while those that have a low availability of coping outlets are more stressful for low-ranking individuals. Habitats that allow subordinates to easily avoid dominants are less stressful, while those that are not conducive to avoidance are generally more stressful for subordinate animals.
This highlights the fact that captive habitats that are not designed to