Chapter 26 – Immune System

Publisher Summary The distribution network of the lymphatic and blood vessels provides a rapid, targeted response to fight the invasion of foreign organisms with a combination of both humoral and cellular defense systems. Successful destruction and elimination of minor infections results in the production of serum antibodies and populations of activated cells, which can more quickly and effectively combat recurrent invasions. The duration of immunity depends on many factors including the age of the fish, type of pathogen and environmental conditions. Piscine oxygen-transporting erythrocytes contain basophilic nuclei. These cells are larger in size and more oblong in shape than their mammalian counterparts. The total concentration of leukocytes is less than that of mammals, ranging between 8,000 and 21,000 cells per cubic millimeter. Lymphocytes make up the majority of the white blood cell population followed by lower concentrations of neutrophilic granulocytes, thrombocytes, and monocytes. As new studies are done, evidence is accumulating that most fish (more advanced that agnathans) possess many of the same basic immunological mechanisms as higher vertebrates including: functional interactions among T lymphocytes, B lymphocytes, a major histocompatibility complex (MHC), immunoglobins, and accessory molecules.