Final answer:
Isoelectric focusing is the method used to distinguish antibodies based on their charge. It separates proteins by their isoelectric point within a pH gradient under an electric field. This technique helps identify differences in the large antibody repertoire and understand antibody specificity and cross reactivity.
Step-by-step explanation:
The simple method for distinguishing antibodies that contain small differences in amino acid composition based on their charge is isoelectric focusing. This technique separates proteins such as antibodies according to their isoelectric point (pI), which is the pH at which a molecule carries no net charge. During isoelectric focusing, antibodies are placed in a gel with a pH gradient and subjected to an electric field. Each antibody molecule will migrate to the position in the gradient where the surrounding pH matches its pI and will then remain focused at that point.
Antibody specificity is determined by the unique variable regions of antibodies that bind to complementary epitopes on antigens. However, some antibodies may exhibit cross reactivity, where they bind to similar epitopes on different antigens, recognizing them due to their molecular similarity. The diverse antibody repertoire within an individual represents the complete collection of antibody specificities and is the basis for the body's adaptive immune response.