Inflammatory hemocytes in Ciona intestinalis innate immune response

Abstract

In the present paper an attempt is carried out to revise Ciona intestinalis inflammatory hemocytes according to their morphology as formerly observed by light and electron microscopy, and taking in account recent reports on innate immunity gene expression. We also examine hemocyte morphofunctional aspects as derived from previous papers that refer to the tunic and body wall inflammatory responses challenged by corpusculate or soluble agents. LPS inoculation into the body wall or treating hemocytes in vitro with LPS have also been taken in account. LPS inoculation stimulated the expression of CiTNF alpha, CiFACIT- alpha chain collagen, CiC3a, CiCD94 and enhanced phenoloxidase activity. These reports allow us to distinguish two main hemocyte types categories: 1. agranular hemocytes, including hemoblasts, circulating lymphocyte-like cells, hyaline amebocytes; 2. granular hemocytes including granulocytes with small granules, granulocytes with large granules, unilocular refractile granulocytes and morula cells. Compartment cells and signet ring cells could be intermediate or terminal states presumably involved in releasing inflammatory factors or tunic matrix components. We suggest that the various hemocyte shapes, as shown by light and electron microscopy, could represent functional states as disclosed in inflamed tissues. Although it cannot be excluded that a same cell expresses multiple activities, it is likely that several populations of a same cell type can exert distinct roles.