Monocytic human leukocyte antigen DR (mHLA-DR) expression levels have been reported to be a marker of immunosuppression and a predictor of sepsis and mortality. There is, however, scant data regarding mHLA-DR monitoring in young infants after cardiopulmonary bypass. Our objectives were to investigate the kinetics of mHLA-DR expression and to determine whether mHLA-DR levels are associated with healthcare-associated infection (HAI) after cardiopulmonary bypass in young infants.
mHLA-DR levels were analyzed by flow cytometry using a standardized method in 49 infants (< 3 months old) with congenital heart disease before and after cardiopulmonary bypass. Results are expressed as the number of anti-HLA-DR antibodies per cell (AB/c).
Postoperative mHLA-DR expression was reduced in all of the infants. Eleven patients (22%) developed HAI and 4 patients (8%) died during the 30-day follow-up. mHLA-DR expression was significantly lower on postoperative day 4 in the HAI group compared to those who without HAI (3,768 AB/c [1,938-6,144] vs. 13,230 AB/c [6,152-19,130]; p = 0.0142). Although mHLA-DR expression is associated with postoperative severity, mHLA-DR ≤ 4,500 AB/c in first 72 hours among patients with higher postoperative severity (extracorporeal membrane oxygenation and/or corticoids and/or delayed closure of sternum) is associated with occurrence of HAI in univariate analysis (OR = 6.3, 95% CI 1.0; 38.7; p = 0.037).
Cardiopulmonary bypass induces a profound decrease in mHLA-DR expression in young infants. Among patients with higher postoperative severity, low level of mHLA-DR in the early postoperative period is associated with the development of HAI.

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