Serum lysozyme activity can differentiate infection from rejection in organ transplant recipients

The presentation of infection in immunocompromised patients can be subtle. Patients often undergo extensive testing and empiric treatment for rejection and infection while awaiting the results of the biopsy and culture results. Delay in diagnosis of either entity can result in a worse clinical outcome. Lysozyme activity has been found to be both a sensitive and a specific marker for infection in laboratory animals and trauma patients. Our goal was to determine whether lysozyme activity could serve as a reliable marker for infection in immunocompromised organ transplant recipients.

Transplant recipients from three clinical categories were enrolled in this study. Group 1 (n = 16) were patients hospitalized for sepsis (culture-positive), and Group 2 (n = 13) for biopsy-proven rejection. Group 3 (n = 51) were recipients who had routine blood sampling in the clinic. In Groups 1 and 2, blood was collected within 24 h of hospital admission and centrifuged, and serum samples were stored at 80 degrees C until processing. Lysozyme activity was assayed by turbidimetric measurement on a sample of a standard suspension (0.15 mg/ml) of Micrococcus lysodeikticus in buffer using a spectrophotometer to read the optical density at 450 nm. The lysozyme activity level was then determined by the measuring activity at 1 min subtracted from activity at 4 min. White blood cell count was determined by using a flow cytometer. Statistical comparisons between groups were made using paired Student's t test.

Serum lysozyme was found to be significantly elevated in Group 1; the mean level of activity was 60.1 +/- 13 (P < 0.05) compared to the level of activity in Group 2, mean 41.1 +/- 11, and Group 3, mean 40.8 +/- 13. A level of 45 units of activity/ml of serum or above indicated infection and not rejection in the patients admitted to the hospital.

These findings indicate that the lysozyme activity assay appears to be useful in differentiating infection from rejection in transplant recipients.