Apoptosis differs in dendritic cell subsets early after severe trauma

Dendritic cells (DC) represent an integral part of the immune system. However it is unclear how apoptosis in myeloid DC (MDC) and plasmacytoid DC (PDC) is affected and whether pro- or antiapoptotic properties dominate during the early post-traumatic phase. Blood samples were obtained on day 1 and day 4 after hospital admission from 10 severely traumatized patients and 10 healthy volunteers. Mononucleated cells were isolated and incubated with LPS. Apoptosis of MDC and PDC was assessed by annexin-V staining using flow cytometry. Expression of genes involved in apoptosis (Caspase-8, Flice inhibitory protein [FLIP], Bcl-2, Bax, Gadd45) in DC was measured by reverse transcriptase polymerase chain reaction. For statistical evaluation, the Kruskal-Wallis test was used (p < 0.05). Severe trauma increased apoptotic MDC compared with those in healthy controls (p < 0.05), whereas apoptosis of PDC was not influenced by the trauma impact. LPS stimulation decreased MDC apoptosis until day 4 after trauma; by contrast, for PDCs this effect was present only on day 1 after trauma. The Bcl-2/Bax ratio in DCs increased significantly. We conclude that peripheral MDCs are more susceptible to undergo apoptosis after trauma compared with PDCs. However, the overall response of DCs early after trauma is characterized by an increased activation of antiapoptotic mediators that might indicate a compensatory life-prolonging reaction.