Antibodies play a role in enhancing body's immune response too, say University of Otago researchers in New Zealand.
Department of Microbiology and Immunology senior lecturer Dr Alexander McLellan says the improved understanding of the immune system resulting from their research may lead to further improvements in vaccine design.
Antibodies, the highly soluble blood proteins are known as the immune system's frontline against fighting pathogens such as bacteria, fungi and viruses through binding to and destroying the invaders.
They are released by specialised white blood cells, called B cells, following vaccination or previous exposure to pathogens and circulate around the body to provide long lasting protection in the blood and solid organs.
Dr McLellan's research group has now shown that B cells use antibody to pull in tiny fragments of pathogens bound to the cell's surface and then recycle these to amplify the immune response.
"Our finding goes some way to explain the largely unsolved mystery of how the immune system gets kick-started. A major outstanding problem in immunology is how small amounts of infectious material can trigger strong immune responses at the start of the infection," Dr McLellan says.
"Instead of destroying these fragments, we were surprised to find that B cells send them out again, still bound to antibody in a lipid particle, to further stimulate the immune system."
The recycled pathogen fragments on these specialised antibody particles trigger other white blood cells involved in initiating the immune response. This contrasts with the extensively studied function of the highly soluble form of antibody, which is known to function exclusively to destroy pathogens, he says.
"We believe our discovery of this recycling mechanism goes someway to explain why the immune system is an incredibly powerful bio-sensor, able to detect nanograms of pathogen material. Essentially, this is same as being able to taste half a teaspoon of instant coffee dissolved in an Olympic swimming pool, such as Dunedin's Moana Pool."
To identify the type of white blood cells involved in the release of the specialised antibody particles, the research group used a sophisticated machine called a flow cytometer.
This $1m state-of-the-art piece of equipment enables high speed purification of cells from complex mixtures, such as blood cell suspensions.
The findings, published in the prestigious Journal of Immunology, are hailed as groundbreaking.