Differences in immune protection presumably explain why some
people exposed to infection resist disease or recover while others
succumb. These authors sought to distinguish the influences
of genes and environment on immunity. They compared the cellular and molecular components
of the immune system among 210 twins: 78 monozygotic (MZ, “identical”) and 27
dizygotic (DZ, fraternal) pairs. They measured
43 serum proteins and 72 immune cell populations repeatedly and longitudinally
(over time) to assess actual variations and account for technical
variations. MZ twins, who have
practically identical genomes, and DZ twins, who share half their genes, are
especially valuable for assessing the relative contributions of “nature or nurture” (genes or environment) to phenotype. Their analysis allowed them to detect as
little as 20% heritability.
The levels of few proteins and cell populations are under
strong genetic control, such as interleukin-6 and CD4+ “central memory” T
cells, but most are only weakly heritable or not at all (Fig 1). They found
that a common, chronic infection, by cytomegalovirus (CMV), influences the levels of most (58%) cell populations and
proteins (Fig 5). Variation
between twins increased as they age, probably reflecting different
environmental stimuli and epigenetic changes (Fig 4). Most intriguing, they correlate the
heritability of response to vaccines to the age of immunization, whereby early childhood vaccines
are highly heritable while vaccines after early adolescence have no detectable heritability
(Table 1, shown below).
