29th Annual Meeting and Symposium of the
Desert Tortoise Council, February 20-23, 2004
Abstracts

Identification and Characterization of the Antigen Presenting Cells' (APC) Receptor CD74 of Mediterranean and Desert Tortoises: Implications in Diagnostic and Health Assessment

F. C. Origgi
Department of Immunology and Infectious Diseases, Human Virology Unit; DIBIT- San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy

During the last decade, reptile medicine has dramatically improved in almost all its branches from diagnostic to therapy and surgery. Nevertheless, the field of reptile immunology has been virtually untouched since the late 70's. Additionally, the extraordinary improvement that human medicine has benefit from the growing knowledge concerning the functions and the structures of the human immune system clearly demonstrate that new efforts need to be done to fill this gap in reptile medicine. In an attempt to acquire some basic data about the molecular players that are pivotal for the functions of the reptile immune system, a complementary DNA (cDNA) library from Testudo graeca Ficoll-purified total white blood cells was prepared. More than a hundred clones were identified and submitted for sequencing. During the sequencing of a first batch of 20 cDNA clones that have been obtained, the antigen presenting cells (APC) receptor CD74 was identified. This cellular receptor is known to be expressed on the surface of all the antigen-presenting cells, particularly on B-lymphocytes and Macrophages. Additionally, CD74 is known to be structurally associated to the immature forms of the major histocompatibility class II (MHCII) molecules that are involved in the antigen presentation to the CD4+ T-lymphocytes. In human immunology CD74 has been characterized as a critical chaperone molecule in directing the correct folding of the MHCII molecules. Additionally, CD74 is critical in the loading of the not-self peptides that are derived from the intra-vesicular degradation of phagocitated microorganism by the APC cells in the MHCII groove itself.

In the attempt to acquire more information concerning the variability and polymorphism of CD74 in other chelonians, the homologous regions of T. hermanni, T. marginata and Gopherus agassizii CD74 were successfully amplified by polymerase chain reaction (PCR) using two primers which were designed on the sequencing information obtained for T. graeca CD74. The comparison of the homologous regions of the CD74 receptor of these four tortoises species showed that this molecule is very conserved in chelonians.

We are currently evaluating if the distribution of this receptor in lymphoid tissues from healthy and diseased tortoises, in the attempt to assess if it is possible to use CD74 as a marker of inflammation and disease.

CD74 is the first ever cell receptor identified in reptiles. The identification of the Mediterranean and Desert tortoises CD74 suggests that reptiles too shares the basic immune response dynamics that have been described in mammals and in humans. The study and the characterization of molecules such as CD74 could reveal the basic functions that control immune response in reptiles and could be used as very specific diagnostic tools to assess the integrity and the efficiency of the immune response itself.