As any chemistry student knows, precipitation occurs when soluble substances interact with one another in solution to form a solid, which comes out of solution and forms a precipitate. In immunology there is a variation on the theme when protein antigens are precipitated out of solution by binding them to specific antibodies, in a process known as immunoprecipitation. This is a neat way of isolating one particular protein antigen about of many thousands in a solution.
This basic biochemistry was transformed with the invention of uniformly spherical microbeads. By attaching antibodies to these beads it was possible to make the process fast and efficient. In 1977, a chemical engineer called John Ugelstad of the Norwegian Institute of Technology in Trondheim, who was prone to thinking about problems late into the night, invented a method of making microbeads without the benefit of the weightless of space – which some researchers believed was a prerequisite for manufacturing spherically uniform beads.
A short while afterwards, while Ugelstad was lecturing in the United States, he was asked if it were possible to make the beads magnetic. A few nights later, he came up with a way to make microbeads that were paramagnetic, in other words magnetic when exposed to a magnetic field and non-magnetic when the field was removed. This greatly increased the efficiency of immunoprecipitation and allowed the process of antigen separation to become highly automated.
They have the advantage over more traditional agarose beads in that they are smaller and so present a bigger volume for binding – as well of course being easily and gently separated in the solution by applying a magnetic field to the side of the test tube.
Immunologists now use magnetic beads routinely, not only for immunoprecipitation but now for isolating different cell subsets for functional studies and flow cytometry.