MBP and IL 5 as markers of eosinophilic granulocytes in circulating blood of the sea turtle Caretta caretta

Eosinophils play a key role in defense against parasites and serve as an important mediator cell in hypersensitivity diseases. Eosinophils of the sea turtles are, generally, rare in the differential count (about 4%) and contain both eosinophilic and colourless granules in their cytoplasm. They were studied by immunocytochemical detection of major basic protein(MBP) and interleukin-5 (IL5) at L.M and TEM in leukocytes of 6 specimens of Caretta caretta. It is well known in Mammals that MBP is a potent enzyme against helminths and is toxic towards bacteria. It activates neutrophils and macrophages, and is implicated in asthma. It forms the electron-dense crystalline core of the specific granules of mature peripheral blood eosinophils (Swaminathan et al., 2005). IL5 is a growth and differentiation factor (Clutterbuck et al, 1989), activator and chemoattractant for eosinophils and, as a consequence, is considered a pivotal cytokine in allergen-mediated eosinophilic responses. Both blood smears and ultrathin sections of the buffy coat were treated with anti-MBP and anti IL5 polyclonal antibodies revealed by ABC method on the smears and by immunogold method for TEM. At LM both MBP and IL5 immunoreactivities were localized in the cytoplasmic granules. IL5 was detected in the cytoplasm of the lymphocytes too. These results were confirmed by TEM observations by showing an intense gold labelling of MBP in the granules, even if most of them are lacking of crystalloid core. IL5 detection displayed less intense immuno- reactivity in the eosinophilic granules and in the lymphocytes