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Identification of cells participating in the defence against pathogens and cellular defence mechanisms during larval development

- Carp immune cells
The ontogenic appearance of carp leucocytes has been revealed. In brief, a very early presence (around hatching during the 2nd day p.f) of macrophages, granulocytes and at 3 dpf the putative "mucosal T cells" were found using antibody staining techniques. Leucocytes were cells found as early as 2 dpf in hematopoietic tissue in the tail region of carp. It appears that the haematopoietic tissue in the tail is far more extensive and contains considerable numbers of B cells and macrophages at an early age (2-4 days pf) compared to haematopoietic tissue in the (head) kidney. 'Mucosal T cells' were not detected in the hematopoietic tissue of the tail, but were found especially in the third segment from the gut, also from 3 dpf. Another monoclonal (WCI12) was used to study B cell ontogeny on a tissue level. Positive cells were found in (head) kidney and spleen from 2 weeks p.f., in gut from 5 weeks p.f., in gills from 6 weeks p.f., and in skin from 12 weeks p.f. To identify the location where and stage when granulocytes (both neutrophilic and basophilic) appear, electron microscopy was used. We found neutrophilic granulocytes between aorta and Vena cardinalis and the posterior blood island (around caudal part of Vena cardinalis) at 48 hours, but not at 24 hours. Basophilic granulocytes were found in tissue suspensions of 3-days-old animals, but in situ they were found somewhat later in 5-days-old animals. The results obtained shed light on the ontogenic appearance of lecocytes which, in turn, could contribute to the development of efficient vaccination and immunostimulation strategies for carp larvae in the future.

- Sea bass immune cells
The sea bass T cell were found to be present in the intestine and thymus 28 dph, head kidney 35 and spleen 45 dph. B cells were present in the head kidney and spleen 45 dph, and in the intestine and thymus 90 dph. This indicate that sea bass larvae can mount a specific immune response not before ca. 45 dph. This has significance on vaccination strategies for sea bass larvae.

- Atlantic halibut immune cells
Ontogenic development of halibut lecucoytes were not studied except the developmental cycle of halibut thymus.

- Atlantic cod larval cells have been characterised by enzyme histochemistry and for their production of antimicrobial susbtances. Embryonic/larval cells were found to contain enzymes important for destruction of microbial components, and could be assayed for e.g. respiratory burst reaction that produces reactive oxygen radicals.

- Spotted wolffish macrophages have been successfully isolated, cultivated and characterised. Simple methods for assaying microbial defence mechanisms have been done. Any presence of macrophages in wolffish embryo have not been found.

For cod, halibut and spotted wolffish it is too early to give an indication of the timing of specific immune responses to occur.

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Universita degli Studi della Tuscia (UNITUS)
Largo dell'Universita, Blocco D
01100 Viterbo
Italy
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