Immunocytochemical Tools Reveal a New Research Field Between the Boundaries of Immunology and Reproductive Biology in Teleosts

Since the specific binding of the antigen and immunoglobulin was discovered, multiple applications have been developed to asses different issues such as: (i) localization of cells and molecules in different cell compartments, (ii) characterization of functional subsets of cells, (iii) identification of different cell types, (iv) and specific blocking or enhancement of receptors or other protein functions (Ruigrok et al., 2011). However, the array of available antibodies specific to fish species has limiting those experiments mostly in lower vertebrates and invertebrates. Mulero and colleagues, in the heart of our research group, has obtained some specific antibodies against several leukocytes and cytokines using different approaches. Moreover, we have developed some immunocytochemical techniques that allowed us to identify the immune cells in the gonads and to study their main activities and their regulation by different molecules or physiological processes in a teleost species, the gilthead seabream (Sparus aurata L.). The gilthead seabream is a sequential hermaphrodite species that, in the western Mediterranean area, develops as male during the first two reproductive cycles, while from the third reproductive cycle onwards the population divides into males and females (Chaves-Pozo et al., 2005a; Liarte et al., 2007) and due to the morphological arrangement of its bisexual gonad, it ́s an interesting model for studying the mechanisms involved in the regulation of the gonads. This chapter deals with the antibodies and the techniques used to set up a novel research line in fish, such as the study of the immune-reproductive interactions which are essential for normal reproductive physiology. The antibodies have been obtained using three different approaches: (i) immunizing mice with cells, (ii) immunizing rabbits with recombinant proteins, or (iii) with synthetic peptides. Moreover, we have also used commercial antibodies in order to achieve information about the renewal of the cells in the gonad, especially analysing processes such as cell proliferation and apoptosis. The results obtained allowed us the identification and functional characterization of the leukocytes and immune molecules located in the gilthead seabream gonads.