11 Jun 2014. Partnership between natural Immunoglobulin G (IgG) and lectins confer immune protection to future infections.
Natural antibodies are present in uninfected individuals and even new-born babies without any previous infection, vaccination or other antigen exposure. They have been an immunology enigma for fifty years. They are widely thought to lack antigen-specificity and affinity for pathogens. The research team led by Professor DING Jeak Ling from the Department of Biological Sciences in NUS has now discovered that the natural Immunoglobulin G (IgG) recognises and attaches to lectins, which are proteins that can bind sugars present on the cell surface of the invading microbes. One type of lectins that have been identified to be active in this study is ficolins. The response is initially triggered by a local increase in the acidity (acidosis), and a decrease in the calcium levels (hypocalcemia) in the blood or tissues caused by the infection. Then the natural IgG binds to the ficolin (see Figure). The bacteria marked this way are finally engulfed by white blood cells in a process known as phagocytosis. Mice which are susceptible to infection can be conferred protection by administration of natural IgG. This indicates its potential use as antimicrobial therapeutics.
This discovery of how natural IgG works to provide immunity under typical infection-inflammation conditions characterised by mild acidosis and hypocalcemia opens a new approach to antimicrobial therapy. The natural IgG in combination with lectins could be potentially developed as a preventive prophylactic drug to combat future bacterial infections.
The research has been published in The EMBO Journal.
Image shows the diagrammatic representation suggesting how natural IgG:ficolin:Fc interaction clears the invading microbe by phagocytosis, with production of IL8. [Image credit: Saswati PANDA]
Panda S, Zhang J, Tan NS, Ho B, Ding JL. "Natural IgG antibodies provide innate protection against ficolin-opsonized bacteria." The EMBO Journal 32 (2013) 2905.