Mannose-binding lectin polymorphisms and susceptibility to infection in systemic lupus erythematosus

Objective. To determine whether variant alleles in the coding portion of th e mannose-binding lectin (MBL) gene are associated with increased susceptib ility to systemic lupus erythematosus (SLE) and concomitant infections. Methods. MBL alleles and serum concentrations were determined by polymerase chain reaction and enzyme-linked immunosorbent assay, respectively, in 91 Danish patients with SLE and in 250 controls. Results. Homozygosity for MBL variant alleles was observed in 7.7% of the S LE patients compared with 2.8% of the controls (P = 0.06), while no differe nce was seen for heterozygosity (33.0% versus 34.4%). Homozygotes had an in creased risk of acquiring serious infections compared with patients who wer e heterozygous or homozygous for the normal allele (odds ratio 8.6, 95% con fidence interval 1.5-47.6, P = 0.01). The time interval from the diagnosis of SLE to the first infectious event was shorter (P = 0.017), and the annua l number of infectious events was 4 times higher, among homozygotes (P = 0. 00002). They were especially prone to acquire pneumonia (P = 0.00004). Conclusion. Homozygosity for MBL variant alleles may explain much of the in creased risk of complicating infections seen in SLE patients, Additionally, it is a minor risk factor for acquiring SLE.