Background. Although there is considerable support for
adverse relationships between states of
psychological and somatic distress and immune response, there is little
evidence in humans of the
relative contribution of genetic and environmental factors.
Methods. This study utilized a twin methodology to examine
the interplay between psychological
distress, fatigue and immune function. We recorded a number of measures
of distress, including
conventional depression and anxiety as well as the somatic symptom of prolonged
fatigue, and
immune responsiveness (by delayed-type hypersensitivity skin response)
in 124 normal adult twin
pairs (79 monozygotic, 45 dizygotic).
Results. While there were strong genetic influences on the
psychological distress and fatigue factors
(only some of which are common to both), familial aggregation of immune
responsiveness arose
mainly from environmental factors shared by both members of a twin pair.
Phenotypic correlations
between psychological and immune measures were negligible, but multivariate
genetic modelling
revealed that these masked larger genetic and environmental correlations
of opposite sign. Negative
environmental effects of psychological distress and fatigue on immune responsiveness
were
countered by a positive genetic relationship between psychological distress
and immune function.
Conclusions. Our study suggests that current psychoneuroimmunological
hypotheses in humans
need to be modified to place increasing importance on the individual's
genotype. In this cohort
immune responsiveness varied in response to a complex interplay of genetic
and environmental
factors. Additionally, although psychological distress and fatigue had
some shared genetic
determinants, independent genetic and environmental risk factors for fatigue
were also identified.