Apoptosis in thymus of teleost fish.

The presence and distribution of apoptotic cells during thymus development and in adult were studied by in situ end-labelling of fragmented DNA in three temperate species carp (Cyprinus carpio), sea bass (Dicentrarchus labrax) and dusky grouper (Epinephelus marginatus) and in the adult thymus of three Antarctic species belonging to the genus Trematomus spp. During thymus development some few isolated apoptotic cell (AC) firstly appeared in the central-external part of the organ (carp: 5 days ph; sea bass: 35 days ph grouper: 43 days ph). Initially the cells were isolated and then increased in number and aggregated in small groups in the outer-cortical region of the thymus larvae. The high density of apoptotic cells was observed in the junction between cortex and medulla from its appearance (border between cortex and medulla, BCM). ACs decreased in number in juveniles and adult as well as the ACs average diameter. In late juveniles and in adulthood, the apoptosis were restricted to the cortex. In Antarctic species the thymus is highly adapted to low temperature (high vascularisation to effort the circulation of glycoproteins enriched plasma and strongly compact parenchyma). The apoptosis process was more extended (4-7 fold) as compare with the thymus of temperate species, even if the distribution of ACs was similar in all examined species. Data suggested a common process of T lymphocyte negative-selection in BCM of thymus during the ontogeny. The selection process seems to be still active in adult polar fish, but restricted mainly in the cortex zone.

Heat shock protein 70 kDa (HSP70) increase in sea bass (Dicentrarchus labrax, L 1758) thymus after vaccination against Listonella anguillarum.

Heat shock proteins 70 kDa (HSP70) and apoptosis were investigated in thymus of sea bass juveniles (Dicentrarchus labrax) subsequently to a vaccination against Listonella (syn. Vibrio) anguillarum. HSP70 expression was measured by immunohistochemistry and immunoenzymatic methods, resulting in increase in HSP70 after bath immunization and persistent in fish exposed to an intraperitoneal (i.p.) booster. The HSP70 increase in thymus was suggested as induction in lymphocytic cells, to be related to immune system stimulation after vaccination. However, a thymic recruitment of lymphocyte subpopulations, characterized by higher expression of HSP70, was also hypothesized after vaccination. No apparent relationships were found between HSP70 and apoptosis. In fact, the vaccination did not modulate the apoptosis response, as measured by TUNEL assay and by immunohistochemistry for active caspase-3 expression. The lack of apoptosis effects could be ascribed to the use of inactivated bacteria that appeared not able to interfere with programmed cell death mechanisms. This manuscript aims to contribute to the knowledge of some biochemical features underlying the immunization, with a particular emphasis on the modulation of HSP70. However, further parameters involved in innate/adaptative immunity and apoptosis pathways have to be taken into account to well establish the functional role of HSP70 in fish vaccination.