Serum complement activity in differentiating between bacterial and viral infections

Abstract

The serum complement system is a humoral part of the innate immune system that takes part in killing pathogens via opsonization, induces inflammation or uses its proteins to form membrane-attack complex (MAC) on pathogens surface leading to its lysis. Complement cascade has three activation pathways: classical-, lectin- and alternative pathway which converge in terminal pathway leading to the formation of MAC. In this study we measured complement activity from patient serum samples provided by TYKS to determine if there is difference between serum samples from patients with bacterial infections and patients with viral infections. The method we used had luciferase-modified Escherichia coli (E.coli-lux), which emits measurable bioluminescence, exposed to the serum samples complement activity. As E.coli-lux emits bioluminescence signal while alive, we could measure the complement activity by measuring the signal produced while the cells die to the lysis. We found out that there were significant differences between the complement activity of bacterial samples and viral samples as well as to the healthy control samples. We did not find any differences comparing the subgroups divided by the diagnosis. The method used for this study is quite simple and fast to perform and could thus be a good addition to the diagnostic methods used in clinical setting to differentiate between bacterial and viral infections. It cannot however be used on its own as there was also overlap between the infection types.