Complex immune system changes observed after traumatic injury

Within the first hour after experiencing a traumatic injury, a person’s immune system undergoes a series of complex, dynamic changes, reveals a new study by researchers at the University of Birmingham. 

Many trauma victims who survive their initial injury die later of multi-organ dysfunction or sepsis — complications related to the massive immune response mounted by the body after trauma. Much of what is known about this immune response is based on blood samples taken from patients after admission the hospital, generally hours after trauma. An ongoing question in the field has been whether immune activation and suppression happen simultaneously or one after the other. 

In the new study, published in PLOS Medicine, Jon Hazeldine and colleagues collected blood samples from 89 adult trauma patients at a regional trauma network in the West Midlands, UK, within an hour of their injury (mean time to sample 42 min, range 17–60 min). Levels of immune cells in those samples, as well as samples collected at later time points, were measured and patient outcomes were tracked. 

The researchers observed that within minutes of a traumatic injury, levels of many immune cells and molecules were altered — in some cases increasing compared to normal and in other cases decreasing. These changes reflected both innate immune cell activation and immune suppression, suggesting that both processes are being induced simultaneously. 

Many of the characteristics of the immune reaction observed in the first hour after trauma were different to those seen at later time points. Moreover, the researchers found an association between natural killer T cell numbers in the hour after trauma and the eventual development of multiple organ dysfunction syndrome. 

“Our study highlights how differences in sample timing can influence our understanding of the post-injury immune response,” the authors said. The results, they added, also underscore “the dynamic nature of the immune response to trauma and show at the functional and phenotypic level that immune alterations consistent with activation and suppression are evident within 1-hour of injury”.