Western blot is a technique to qualitatively assess the immune response of a patient to antigens. Antigens are usually bound to a membrane and the antigen that are recognized by antibodies present in a patient’s blood sample are visualized. Depending on the number of detected antigens it can be concluded if a patient had exposure to a disease.
Generally, a mix of proteins is separated by size and are transferred on a membrane. This process is called blotting and lends the name to this testing method. An enzymatic reaction is used to visualize bound antibodies. The separation of proteins makes it possible to distinguish specific antigens that are recognized by the immune system. And it is often seen that with longer progression of disease more antigens get recognized by a patient’s immune system.
Each of these tests has two components for determining the type of infection whether it is current or a past infection using Sub-classes of antibodies. IgM antibodies are built quickly after exposure to foreign antigens and it is followed later by antigen specific IgG antibodies. IgM subclass is thought to be a quick way of aiding the body fight an infection and giving the body time to develop a more specific antibody response in form of the IgG subclass.
IgM is shown to be positive if you have had a recent or active infection that your body is currently trying to fight off. While IgG is generally shown to be positive if an infection is currently fought or it was in the past.