GIVING the immune system a broad education helps it cope with invaders that
change their appearance, the meeting heard last week.
Mutating viruses are a major headache for vaccine designers, partly because
of a phenomenon known as 鈥渙riginal antigenic sin鈥�. Immunisation against one
strain of a virus鈥攖he 鈥渙riginal sin鈥濃�攎ay inhibit the immune response
to a different strain, just as Adam鈥檚 bite of the apple supposedly had
consequences for us all. 鈥淚n these cases no vaccine might actually be better
than the wrong one,鈥� says David Anderson of the University of California,
Davis.
Anderson and his colleagues Maria Carlos and Jose Torres wondered if vaccines
that contain thousands of small proteins representing many strains might
overcome this problem. They prepared a pot-pourri of 32 000 peptides from SIV,
the primate relative of HIV, and used it to immunise mice. As controls, they
immunised two other groups of mice with a single peptide each from two strains
of SIV not included in the peptide mixture.
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They then gauged what fraction of the mice鈥檚 CD4 cells were stimulated by
inactivated SIV鈥攁 standard measure of immune response. In mice immunised
with a peptide from the same strain of SIV, 1 per cent of the cells were primed
for action. Mice immunised with a peptide from another strain had 0.3 per cent
of their cells activated鈥攂arely above background activity levels.
But in mice given the peptide mixture, an impressive 2.3 per cent of the
cells responded to the viral newcomer. Anderson thinks exposure to many
different peptides encourages the immune system to develop cells with a much
broader repertoire of possible targets.
