Identical point mutation leading to low levels of mannose binding protein and poor C3b mediated opsonisation in Chinese and Caucasian populations

Abstract

A common opsonic defect occurring in 7% of the Caucasian population is associated with low serum levels of the lectin mannose binding protein (MBP). This study sought to determine whether the deficiency was also present in a Chinese population using sera obtained from 100 healthy Chinese children (age range 6 weeks-16 years). The distribution profiles of MBP levels and C3b/C3bi fragments binding to mannan coated plates were both bimodal and similar to the corresponding Caucasian profiles. Serum MBP levels were low in 9% of the Chinese children and all of these sera generated low levels of C3b/C3bi fragments. Overall there was a high significant correlation between MBP levels and C3b opsonin generation (r = 0.77; P < 0.001). By analogy with similar findings in a Caucasian population we believe this correlation to be a reflection of antibody independent complement activation by MBP. In a pilot study of DNA obtained from three adult Chinese with low MBP levels the point mutation causing MBP deficiency in Caucasians was identified in all three cases.