Infection imposes a serious burden on patients with
systemic lupus erythematosus (SLE). The increased
infection rate in SLE patients has been attributed in part to defects of immune defence. Recently, the
lectin pathway of complement activation has also been suggested to play a role in the occurrence of
infections in SLE. In previous studies, SLE patients homozygous for
mannose-binding lectin (MBL) variant alleles were at an increased risk of acquiring serious
infections in comparison with patients who were heterozygous or homozygous for the normal allele. This association suggests a correlation between functional MBL level and occurrence of
infections in SLE patients. We therefore investigated the biological activity of MBL and its relationship with the occurrence of
infections in patients with SLE. Demographic and clinical data were collected in 103 patients with SLE. Functional MBL serum levels and MBL-induced C4 deposition were measured by
enzyme-linked
immunosorbent assay using
mannan as coat and an MBL- or C4b-specific
monoclonal antibody. The complete MBL-dependent pathway activity was determined by using an assay that measures the complete MBL pathway activity in serum, starting with binding of MBL to
mannan, and was detected with a specific
monoclonal antibody against
C5b-9. Charts were systematically reviewed to obtain information on documented
infections since diagnosis of SLE. Major
infections were defined as
infections requiring hospital admission and
intravenous administration of
antibiotics. In total, 115
infections since diagnosis of lupus, including 42 major
infections, were documented in the 103 SLE patients (mean age 41 +/- 13 years, mean disease duration 7 +/- 4 years). The percentage of SLE patients with severe
MBL deficiency was similar to that in 100 healthy controls: 13% versus 14%, respectively. Although deposition of C4 to
mannan and MBL pathway activity were reduced in 21% and 43% of 103 SLE patients, respectively, neither functional MBL serum levels nor MBL pathway activity was associated with
infections or major
infections in regression analyses. In conclusion, SLE patients frequently suffer from
infections, but deficiency of functional MBL does not confer additional risk.