The immune system is split into innate and acquired immunity, with acquired immunity being further divided into humoral and cell-mediated immunity (CMI). Humoral immunity involves antibodies, of which there are five types. Antibodies are important for helping destroy antigens in a range of ways and are produced by B-lymphocytes. Humoral immunity and CMI work together to protect the animal, with components of CMI being essential for mediation of the acquired immune system. Humoral immunity can be measured using serological tests, which have applications in disease diagnosis and assessment of the need for revaccination.