Cytochemical aspects of the peripheral blood cells of Oreochromis (Tilapia) niloticus. (Linnaeus, 1758) (Cichlidae, Teleostei): part II

Aspectos citoquímicos das células do sangue periférico de Oreochromis (Tilapia) niloticus. (Linnaeus, 1758) (Cichlidae, Teleostei): parte II

Cytochemical aspects of the peripheral blood cells of Oreochromis (Tilapia) niloticus. (Linnaeus, 1758) (Cichlidae, Teleostei) - Part II

Aspectos citoquímicos das células do sangue periférico de Oreochromis (Tilapia) niloticus. (Linnaeus, 1758) (Cichlidae, Teleostei) - Parte II

Ivete Kotomi UEDA¹; Mizue Imoto EGAMI¹; Wilson da Silva SASSO¹; Eliana Reiko MATUSHIMA²

CORRESPONDENCE TO:

Eliana Reiko Matushima

Departamento de Patologia da

Faculdade de Medicina Veterinária e

Zootecnia da USP

Av. prof. Dr. Orlando Marques de

Paiva, 87 - Cidade Universitária

Armando de Salles Oliveira

05508-000 - São Paulo - SP

ABSTRACT

Morphologicaly, seven types of cells were identified in the blood of Oreochromis niloticus: erythrocytes, thrombocytes, neutrophils, eosinophils, basophils, lymphocytes and monocytes. Glycogen was present not only in the cytoplasm of neutrophils and thrombocytes but also in some lymphocytes and monocytes. The positive reaction for myeloperoxidase and Sudan black was observed in neutrophils and eosinophils. The bromphenol blue method was strongly positive for erythrocytes and eosinophils.

UNITERMS: Blood cells; Cytochemistry; Oreochromis niloticus; Fishes.

INTRODUCTION

Interest in fish as laboratory animals has increased considerably in the last few decades. There have been several investigations on their physiology, biochemistry and pathology^17,23,30. Concerning the haemoichthyology the works of Oria³³ and Phillips³⁵ and Black et al.⁴ acted as pioneers, they established a comparison of the haematological aspect among several species of fish. In the following decades, many studies have been performed to establish the haematology index of teleost fish^6,15,22. Studies on the erythrocyte lineage cells have been carried out by Mcknight²⁸; Ezzat et al.¹⁵; Imagawa et al.²⁰ and Ueda et al.⁴⁰.

Other authors^{6,20,36,40,41,42}, have studied fish erythrocyte morphology. In relation to the absolute values of erythrocytes there have been some data that were published by McCarthy et al.²⁷; Ribeiro³⁶; Oladimeji et al.³²; Ueda et al.⁴⁰ and Veiga⁴¹ wich may be mentioned.

For thrombocyte Ribeiro³⁶; Imagawa et al.²⁰ and Ueda et al.⁴⁰ have described differences in their number and morphology. Fish blood thrombocytes have been described as the most abundant blood cells after erythrocytes, very little has been revealed about their morphology features and functional properties, the available data on the percentage of trombocytes in fish peripheral blood being very confused because of identification difficulty between lymphocytes and thrombocytes. Other authors have demonstrated a special interest in the leucocytes of fish with regard to their morphological observations and their absolute values, considering a great diversity of morphological aspects to the some type of leucocyte^{5,13,15,16,20,38,40,41}. Therefore the momenclature concerning teleost leucocyte is confusing¹⁴. Neutrophils have been designated with various synonyms such as heterophils⁴³, polymorphonuclear leukocyte² and type I granulocyte¹⁰. For the present study, neuthrophil will be the preferred term. A distinction between monocytes and macrophages is also appropriate to clarify the differences between these cells. Monocytes are relatively immature cells present in hemopoietic tissue and circulating blood.

Althrough, it is very important to establish a classification of leucocytes for histopathological examination of disease fish and for experimental study of inflamation on immunopathology, insufficient studies have been mad on several aspects including fine structure research of teleost fish leucocytes.

The cytochemical aspects of blood cells have been described in different species of fishes by Blaxhall and Daisley⁵; Barber amd Westermann³; Ribeiro³⁶; Caxton-Martins⁷; Doggett et al.⁹; Zinkl et al.⁴⁴; Veiga⁴¹ and Pacheco³⁴, have been described indifferent species of fishes by have studied this aspect for various species of fish.

However, little is known about the cytochemistry of Oreochromis niloticus; so, the present study aimed at investigate the normal morphology of the cellular blood components and the basic data on the cytochemical characteristics for this species.

MATERIALS AND METHODS

Ten Oreochromis niloticus, both male and female were kept in aerated water at the environmental temperature. Their weight varied from 135 g to 370 g and their length from 20,0 cm to 27,5 cm. The animals were anesthetized with benzocain 1/10.000 and blood samples (2ml) were taken from caudal vein in the presence of anticoagulant EDTA for the morphological and cytochemical studies. The blood samples were collected from December to March, that is, in summer time, when the temperature of the water was around 20ºC. For the morphological study blood smears were submitted to Wright staining.

For the cytochemical study blood smears were submitted to the following methods: glycogen demonstration by the Periodic Acid-Schiff PAS²⁹ method and treatment with salivar amylase as a control²⁶, myeloperoxidase demonstration by the Orto-toluidin method in the presence or absence of hydrogen peroxyde²¹, lipidic identification by the Sudan black B²⁶ method and the Bromphenol blue method³¹ for basic protein.

RESULTS AND DISCUSSION

In relation to the morphological elements of peripheral blood of Oreochromis niloticus, it was possible to identify the following cells: erythrocytes, thrombocytes, neutrophils, eosinophils, basophils, lymphocytes and monocytes⁴⁰. The criteria used to define the nomenclature of these cells were based on the morphological aspect of the nucleus and the distribution pattern of cytoplasmic granules as well as the staining ability.

The predominant shape of erythrocyte found in Oreochromis niloticus was elliptical. The nucleus was also elliptical and centrally located with heterochromatin stained in purple and acidophilic cytoplasm. The immature slapes found by some authors are supposed to be due to the acceleration of erythropoiesis process in different physiological conditions in different species.

The neutrophils were spherical and of several sizes with abundant basophilic cytoplasm showing few azurophilic granules. The spherical nucleus was small, purple and in general eccentrically located. Ribeiro³⁶ and Doggett and Harris¹⁰ considered the neutrophil as a highly phagocytic cell ingesting both carbon particles and bacteria. The Oreochromis niloticus eosinophils were spherical of various sizes, and had abundant cytoplasm filled with large acidophilic granules of different sizes. The purple stained heterochromatin filled all the nucleus which in general was centrally located, but occasionally in an eccentric position. The basophils were spherical, the cytoplasm being rich in strongly basophilic granules of various sizes and metachromatically stained. The nucleus was spherical and purple stained. Sometimes, the nuclear outline could not be distinguished due to the presence of these granules.

There are no conclusive data in the literature about the possible functions of eosinophils and basophils in fish blood. In some fish, eosinophils appear to be plagocytotic^18,39 and accumulate in parasitic infections and in inflammation^24,25.

The spherical lymphocytes were of several sizes, with little basophilic cytoplasm and frequently showed cytoplasmatic blebs, and some azurophilic granules. The nucleus was spherical, purple and filled most of the cell. Ellis^13,14 showed the presence of immunoglobulin molecules attached to the surface of lymphocytes similar to those of the upper vertebrates, suggesting them to be immunocompetent cells. Sigel et al.³⁷ reported some evidences on the ability of fish lymphocytes to recognize and to respond to human interleukin-1.

The monocytes were predominantly spherical with irregular outline. The cytoplasm was abundant and basophil, with some azurophilic granules. The nucleus with euchromatic feature was large, usually spherical or sometimes reniform and eccentrically. As to the function of monocytes, Imagawa et al.²⁰ observed their ability to ingest carbon particles thus supporting the results of Ellis¹³; Fergunson¹⁶ and Doggett and Harris¹⁰.

The Oreochromis niloticus thrombocytes were elliptical and their nuclei were also elliptical and centrally located. The heterochromatin stained purple. The cytoplasm was slightly acidophilic and showed clear round small areas at the poles. Occasionally some spherical shapes were found.

The cytochemistry study of the blood cells in Oreochromis niloticus demonstrated the presence of glycogen not only in the cytoplasm of neutrophils and thrombocytes (Fig. 1) but also in some lymphocytes and monocytes. It is supposed that glycogen mainly in neutrophils and monocytes could be related to the phagocytosis process whose mecanism depends on energy. As to the presence of glycogen in the thrombocytes we believe that this substance represents an energetic source for this cell, since some authors like Ferguson¹⁶ and Imagawa et al.²⁰, reported the participation of thrombocyte in the phagocytosis mechanism of foreign substances. This process requires the consumption of energy both from endogenous and exogenous source¹².

Imagawa et al.²⁰ reported in Cyprinus carpio the presence of cytoplasmic vacuoles containing superficial microvilli and carbon particles, thus suggesting the participation of thrombocytes in phagocytosis. Catton⁶ pointed out the presence of haemoglobin in the thrombocyte cytoplasm, whereas Doggett and Harris¹⁰ reported the participation of thrombocyte in the coagulation process of Oreochromis mossambicus.

In relation to the positive reactivity for mieloperoxidase found in neutrophils (Fig. 2) it is certainly related to the known efficient bactericidal system (H2O2-MPO-halide system) used as a defensive mechanism similar to that one observed in mammals⁸. Possibly the eosinophil positive myeloperoxidase activity could be also related to similar oxygen dependent bacteria killing mechanism as suggested by Hoar et al.¹⁹.

The positivity of the Sudan method to the neutrophils and the eosinophils (Fig. 3) to detect phospholipids, is not in agreement with the one found by Doggett et al.⁹, who detected sudanophilic granules only in neutrophils, probably due to the differences in membrane constituents among teleost species.

The Bromphenol blue method for proteins was strongly positive for erythrocytes and eosinophils (Fig. 4). In particular, the positivity observed in the eosinophilic granules, may be due to the presence of antilarval substance-like referred classically as major basic protein (MBP)¹¹ or as eosinophilic cationic protein (ECP)¹ for human.

This research forms the basis of continuing investigations in the functions of these cells in the cellular immune responses.

RESUMO

Morfologicamente foram identificados no sangue de Oreochromis niloticus sete tipos de células: eritrócitos, trombócitos, neutrófilos, eosinófilos, basófilos, linfócitos e monócitos. Em relação aos resultados citoquímicos foi contastada a presença de glicogênio em neutrófilos, trombócitos e em alguns linfócitos e monócitos. Os grânulos citoplasmáticos de neutrófilos e eosinófilos mostraram positividade para mieloperoxidade e Sudan black. O azul de bromofenol foi totalmente positivo em eritrócitos e eosinófilos.

UNITERMOS: Células sangüíneas; Citoquímica; Oreochromis niloticus; Peixe.

Received: 08/05/2000

Accepted: 31/01/2002

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¹

- Departamento de Morfologia da Universidade Federal de São Paulo - EPM ¾ SP

²

- Departamento de Patologia da Faculdade de Medicina Veterinária e Zootecnia da USP - SP

Publication Dates

• Publication in this collection
  17 June 2002
• Date of issue
  2001

History

• Accepted
  31 Jan 2002
• Received
  08 May 2000