Mannan binding lectin in febrile adults: no correlation with microbial infection and complement activation.

Aims: To study the role of the mannan binding lectin (MBL) pathway of complement activation in the host defence to microbial infection in vivo, and the role of MBL in infectious mortality in non-selected patients. Methods: A prospective observational study on 177 hospitalised medical patients with new onset fever. The presence, origin, and microbial cause of infection, the circulating MBL and complement activation product 3a (C3a), and the 28 day hospital course were determined. Results: The patients had median MBL values similar to healthy blood donors: 18% of the patients and 14% of the blood donors had MBL deficiency, with values below 0.1 mug/ml. Median C3a was higher in patients with microbiologically confirmed infection than in those without, whereas there was no difference in MBL values or frequency of deficiency among patient groups with or without positive local cultures or bacteraemia. The mortality rate was 8% and the outcome groups did not differ in MBL. In febrile adults hospitalised in internal medicine wards, microbial infection induces complement activation, independently of MBL. Conclusions: The results argue against a predominant role for the MBL pathway of complement activation and a deficiency of MBL predisposing to serious and invasive microbial infection in non-selected adults.