Total recall for T cells

Scientists track down protein which helps the immune system remember.

Mercifully, the mammalian immune system has a prodigious memory for pathogens. This, of course, is the basis of all vaccines. For decades, however, scientists have been stumped by the question of how cells are capable of such feats of remembering - sometimes years or even decades after the original encounter with an alien bacterium or virus.

Now a group of US and Austrian researchers has tracked down the answer: a protein called CD8aa that marks out a tiny fraction of cells involved in the original immune response for survival. These so-called ’memory’ T-cells go on to recall their encounter and reactivate the immune system should the body subsequently meet that pathogen again. ’Why one T cell is selected and not the other is still not fully understood’, says Hilde Cheroutre, one of the team involved in the research. ’One factor is the strength of the antigen recognition by the particular T cell . the better the recognition, the more likely it is that this T cell will induce CD8aa and survive the initial activation and transform to a memory T cell.’ The researchers found that although only a small portion of cells expressed CD8aa during the initial encounter, the protein was expressed by most T cells involved in the ’recall’ immune response. In studies of ’knockout’ mice, in which CD8aa was deleted, the protein plays an active role in generating memory T cells.

Cheroutre hopes that the work will have important implications for future vaccines: ’The amount of CD8aa induction could be an indicator of the effectiveness of the vaccine. In other words, the more memory T cells are generated during the initial response, the stronger the memory will be . If we better understand what is involved in the decision to select for these CD8aa memory precursors we will be able to improve vaccines based on that information.’

The work should also offer other insights into situations when the body’s immune system apparently goes haywire and starts attacking itself, as in autoimmune diseases and during tissue rejection.

Cath O’Driscoll