LJUBLJANA, SLOVENIA – During their first 4 days in the pediatric ICU, critically ill children have significantly reduced human leukocyte antigen (HLA)–DR expression within all three major subsets of monocytes. The reductions are seen regardless of whether the children were admitted for sepsis, trauma, or after surgery, Navin Boeddha, MD, PhD, reported in his PIDJ Award Lecture at the annual meeting of the European Society for Paediatric Infectious Diseases.
The PIDJ Award is given annually by the editors of the Pediatric Infectious Disease Journal in recognition of what they deem the most important study published in the journal during the prior year. This one stood out because it identified promising potential laboratory markers that have been sought as a prerequisite to developing immunostimulatory therapies aimed at improving outcomes in severely immunosuppressed children.
Researchers are particularly eager to explore this investigative treatment strategy because the mortality and long-term morbidity of pediatric sepsis, in particular, remain unacceptably high. The hope now is that HLA-DR expression on monocyte subsets will be helpful in directing granulocyte-macrophage colony-stimulating factor, interferon-gamma, and other immunostimulatory therapies to the pediatric ICU patients with the most favorable benefit/risk ratio, according to Dr. Boeddha of Sophia Children’s Hospital and Erasmus University, Rotterdam, the Netherlands.
He reported on 37 critically ill children admitted to a pediatric ICU – 12 for sepsis, 11 post surgery, 10 for trauma, and 4 for other reasons – as well as 37 healthy controls. HLA-DR expression on monocyte subsets was measured by flow cytometry upon admission and again on each of the following 3 days.
The impetus for this study is that severe infection, major surgery, and severe trauma are often associated with immunosuppression. And while prior work in septic adults has concluded that decreased monocytic HLA-DR expression is a marker for immunosuppression – and that the lower the level of such expression, the greater the risk of nosocomial infection and death – this phenomenon hasn’t been well studied in critically ill children, he explained.
Dr. Boeddha and coinvestigators found that monocytic HLA-DR expression, which plays a major role in presenting antigens to T cells, decreased over time during the critically ill children’s first 4 days in the pediatric ICU. Moreover, it was lower than in controls at all four time points. This was true both for the percentage of HLA-DR–expressing monocytes of all subsets, as well as for HLA-DR mean fluorescence intensity.
In the critically ill study population as a whole, the percentage of classical monocytes – that is, CD14++ CD16– monocytes – was significantly greater at admission than in healthy controls by margins of 95% and 87%, while the percentage of nonclassical CD14+/-CD16++ monocytes was markedly lower at 2% than the 9% figure in controls.
The biggest discrepancy in monocyte subset distribution was seen in patients admitted for sepsis. Their percentage of classical monocytes was lower than in controls by a margin of 82% versus 87%; however, their proportion of intermediate monocytes (CD14++ CD16+) upon admission was twice that of controls, and it climbed further to 14% on day 2.
Among the key findings in the Rotterdam study: 13 of 37 critically ill patients experienced at least one nosocomial infection while in the pediatric ICU. Their day 2 percentage of HLA-DR–expressing classical monocytes was 42%, strikingly lower than the 78% figure in patients who didn’t develop an infection. Also, the 6 patients who died had only a 33% rate of HLA-DR–expressing classical monocytes on day 3 after pediatric ICU admission versus a 63% rate in survivors of their critical illness.
Thus, low HLA-DR expression on classical monocytes early during the course of a pediatric ICU stay may be the sought-after biomarker that identifies a particularly high-risk subgroup of critically ill children in whom immunostimulatory therapies should be studied. However, future confirmatory studies should monitor monocytic HLA-DR expression in a larger critically ill patient population for a longer period in order to establish the time to recovery of low expression and its impact on long-term complications, the physician said.
Dr. Boeddha reported having no financial conflicts regarding the award-winning study, supported by the European Union and Erasmus University.
SOURCE: Boeddha NP et al. Pediatr Infect Dis J. 2018 Oct;37(10):1034-40.
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