MANNOSE-BINDING LECTIN
LAU
Yu-Lung
Department
of Paediatrics, The University of Hong Kong, Queen Mary Hospital, Hong Kong
Mannose-binding
lectin (MBL), a serum protein characterised by both collagenous regions and
lectin domains, plays an important role in innate immunity as well as
modulating a wide range of infectious and autoimmune diseases. It binds to repeating sugar arrays
on microbial surfaces, thereby activating the complement system via an associated
serum serine protease. Serum
MBL levels are influenced by 3 mutations clustered in exon 1 of the gene
and further modulated by promoter polymorphisms. Mutations and their frequencies differ in different
ethnic groups. Children with
such mutations are at an increased risk of infections. We have established an association
between low MBL levels and these mutations with autoimmune diseases such as
systemic lupus erythematosus and rheumatoid arthritis. Recently we also found an increased
risk of disease progression in hepatitis B virus infected patients with low
serum MBL levels and these mutations.
It has been suggested that these mutations may be associated with
some biological advantage in infection with Mycobacterium
tuberculosis but the data are
still controversial.
Mechanisms through which MBL modulate these autoimmune and
infections diseases are unclear but may be mediated at the interface of
innate and acquired immunity through cytokines modulation. Replacement therapy with MBL for
patients with profound MBL deficiency and increased susceptibility to
infections is being actively pursued.