Early decrease in surface expression of HLA‐DQ predicts the development of infection in trauma patients

The behaviour of human leucocyte antigen‐DR (HLA‐DR) following injury has been extensively studied. However, the behaviour of other class II antigens following trauma has not been characterized as well, despite evidence that HLA‐DQ genotype influences the response to several bacterial antigens. Our study attempts to characterize and analyse the behaviour of HLA‐DQ after trauma in patients with and without infection. Twenty‐five patients were studied following major injury. Fifteen of the 25 patients developed infection (men = 11, women = 4); 10 patients developed no infection (men = 9, women = 1). The mean age was 34 ± 12 years for patients with no infection and 52 ± 20 years for those with infection. Monocyte HLA‐DQ surface expression was determined using FITC‐labelled antibodies and flow cytometry. Expression was compared with a control population of 11 healthy volunteers. The percentage of monocytes expressing HLA‐DQ following trauma was reduced in patients with infection and in those without infection, but returned to normal (days 8–14) only in those patients who did not develop infection. Monocyte HLA‐DQ mean channel fluorescence was reduced on day 1, but quickly returned to normal in those patients who subsequently developed infection. Stimulated with lipopolysaccharide, the initial samples of 13 patients who developed infection showed that surface expression on these monocytes could be elevated into the normal range. We conclude that HLA‐DQ is an additional early marker of outcome that may not function merely as an immune suppressor. The maintained ability of HLA‐DQ to present self‐antigens may be important in the initial stages of the host response to injury.