Mannose-binding lectin (MBL) deficiency and tuberculosis infection in patients with ankylosing spondylitis

Ankylosing spondylitis (AS) patients may have higher prevalence of mannose-binding lectin (MBL) deficiency than normal individuals. MBL deficiency may influence susceptibility to infections. The aim of the study was to verify if MBL deficiency in patients with AS predisposes to infections. We studied 60 patients with AS diagnosed according to the Assessment of SpondyloArthritis international Society (ASAS) criteria. These patients had their MBL serum levels determinated. Twenty-five individuals were identified as MBL deficient (serum values 100 ng/mL). These patients were paired with 35 "sufficient" MBL producers (median serum level = 700 ng/mL; range 150-4100 ng/mL) for gender, age, use of medications, and tobacco exposure. Medical records of all patients were retrospectively investigated for the period of 5 years and the rate of infection occurrence was compared in the two groups. AS patients with MBL deficiency had higher number of urinary tract infections (p = 0.03; IRR = 2.33; 95% CI = 0.95-6.04) and tuberculosis (p = 0.008; IRR = 9.8; 95% CI = 1.2-441.6) than controls. Regarding tuberculosis infection, one patient (2.8%) in the MBL-sufficient group and six (24.0%) from the deficient group had this infection. The MBL-sufficient patient and five from the deficient group have had latent infections, detected in the screening tests done previous to anti-TNF drug use. The other, in the deficient group, had lung infection while not on anti-TNF treatment. Another patient, from the deficient group, has had tuberculosis skeletal infection in the past. We found a significant association between MBL deficiency and higher risk of tuberculosis and urinary tract infection in patients with AS. More studies with higher number of patients are needed to confirm this finding.