2.1 Serology

Serology is the study of antibodies in blood serum and body fluids. It also relates to how antibodies can be used to distinguish between different pathogens and different strains of a pathogen. Serum, in this context, is the fluid component of blood containing soluble molecules such as antibodies and other proteins. Serum is formed after blood has clotted, removing the cellular elements of blood (red cells, white cells) and other components involved in formation of the clot (platelets and proteins of the blood clotting system).

Serum should be distinguished from blood plasma which lacks cells, but which retains the components required for clotting. The pie chart in Figure 2 shows the relative amounts of the proteins in plasma.

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Figure 2 The protein components of plasma

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A colour pie chart showing the labelled protein components of plasma. Starting at the bottom and working round clockwise, albumin comprises just over half of the pie chart. The immunoglobulins (IgG) comprise about one sixth of the pie chart. Transferrin, fibrinogen, IgA, alpha 2 macroglobulin, IgM, alpha 1 antitrypsin, haptoglobin, alpha 1 acidic glycoprotein and apolipoproteins A-1 and A-11 decrease in abundance and collectively constitute about a quarter of the pie chart, while the pool containing medium-and-low-abundance proteins constitute about a twelfth of the pie chart.

Figure 2 The protein components of plasma

As you can see, the three major classes of antibody (IgG, IgA, IgM) constitute about 25% of the total plasma protein.