The dendritic cell lectin DC-SIGN (red) binds to carbohydrate structures on the neutrophil integrin Mac-1 (green).

On page 1281, van Gisbergen and colleagues describe for the first time a direct interaction between neutrophils and dendritic cells (DCs). The event triggers DC activation, primes T helper 1 (Th1) cells, and may help explain why Th1 responses to some pathogens are impaired in the absence of neutrophils.

Neutrophils have been shown to influence the priming of Th1 responses indirectly: they secrete cytokines and chemokines that promote Th1 responses and recruit DCs into infected tissues. But van Gisbergen et al. now show that neutrophils don't always keep their distance. They can interact with DCs directly through binding of the C-type lectin DC-SIGN on DCs to specific carbohydrate structures on the neutrophil integrin Mac-1.Neutrophil–DC binding triggered activation of the DCs as measured by DC up-regulation of CD86 and secretion of interleukin-12. But this only happened if the neutrophils were first activated, suggesting that DC activation only occurs in an inflammatory setting. Neutrophil-activated DCs went on to prime interferon-γ–producing Th1 cells.

One possible consequence of this interaction, the authors speculate, might be transfer of antigens from the neutrophils to the DCs, although this idea remains to be tested. Another open question is whether neutrophils receive signals as part of the relationship with DCs.