An antibody (also known as an immunoglobulin) is part of our body’s response to a foreign molecule or pathogen (also known as an antigen) such as a virus or bacterium. This is valuable to fight off infection. Protective antibodies can provide immunity so we do not become reinfected with the same viruses or bacteria. Antibodies are vital for our health.
Yet, we don’t always develop antibodies—or the right or sufficient antibodies—to fight off all infectious diseases. For example, people infected with HIV or hepatitis C virus do not usually develop protective antibodies.