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Infants (black lines) have more powerful T reg cells that suppress SIV-fighting CD4+ T cells.
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HIV infection tends to develop into AIDS more quickly in infants than in adults. A study by Hartigan-O'Conner et al. (page 2679) now suggests that more potent infant regulatory T (T reg) cells are to blame.
T reg cells cool down virus-induced immune responses by suppressing activated T cells. It has been suggested that too much suppression allows HIV to get the upper hand. Others, however, have suggested that activated T cell suppression by T reg cells prevents inflammatory T cell cytokines from damaging tissues and thus enhancing disease.
Hartigan-O'Conner and colleagues now show that healthy infant monkeys have more—and more potent—T reg cells than do adult monkeys. When monkeys were infected with SIV—the primate version of HIV—most of the infants rapidly developed AIDS. Their T reg cells suppressed anti-SIV T cell functions, whereas the adult T reg cells did not.
Humans also have more T reg cells during infancy. The authors suspect that, like primate T reg cells, the potency of human T reg cells might also decrease with age. Determining why T reg cell numbers decrease with age and why aging T reg cells lose their steam is the next step. 
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