Norepinephrine and octopamine: linking stress and immune function across phyla

In species from three widely divergent phyla (Arthropoda, Mollusca and Chordata) tyrosinederivatives (norepinephrine or octopamine) mediate a response to acute stress. Part of thisresponse is a change in immune function that results in a decrease in resistance to pathogens. Thisdecrease in disease resistance appears maladaptive. However, if the connections betweennorepinephrine/octopamine and immune function were maladaptive, they should have been selectedagainst. None of the four commonly proposed adaptive explanations for acute stress-induced changesin immune function fit the available data for species from all three phyla. However, this result isprobably due to the lack of information about acute stress-induced immunosuppression ininvertebrates and a lack of ecologically valid studies in vertebrates. Understanding why immunefunction and disease resistance changes during acute stress will require greater comparative study.