Neutrophil granules of red seabream Pagrus major with a symptom of cloudiness on the dorsal skin

皮膚背面に白濁症状を呈するマダイの好中球顆粒

Neutrophil granules of red seabream Pagrus major with a symptom of cloudiness on the dorsal skin

Creators Kondo Masakazu

Creators Watanabe Riho

Creators Tachibanagi Keito

Creators Kimura Takehiro

Creators Yasumoto Shinya

Red seabream Pagrus major cultured in our laboratory showed a symptom of cloudiness on the dorsal skin around the base of dorsal fin in June 2020. In the whitish skin, epithelial cells were enlarged with no proliferation. Mucus cells were not observed in the epithelium. Numerous lymphocytes accumulated in the dermis under the epithelium. Photobacterium damselae damselae was isolated from the whitish skin surface, however, the symptom (whitish skin) was not reproduced by experimental infection (immersion method) of this bacterium. Here, we call this disease dorsal skin cloudiness (DSC). Two types of granules were observed in the neutrophils of red seabream infected with DSC. Both granule types had similar morphologies but different cytochemical characteristics to those of ordinary granules (oG1^N, oG2^N) isolated from non-infected fish. In this paper, we called the two granule-types from the fish with the symptom of DSC as extraordinary chromophobic granules (type 1, eoG1^{DSC}： type 2, eoG2^{DSC}). The eoG1^{DSC} showed chromophobic, simple morphology (without stratified structure), peroxidase positive and lack of lysozomal enzymes. The eoG2^{DSC} was stratified granule with three-layer structure [inner eosinophilic layer (L0-0), middle chromophobic layer (L0-1) and outer chromophobic layer (L1)]. Lysozomal enzymes (acid phosphatase, β-glucuronidase and exterases ) and peroxidase (PO) were localized in L0-0 and L1, respectively. Both types of extraordinary granules were Sudan black B negative. Spot formation, a characteristic phenomenon seen in PO-stained oG2^N (positive L1 and negative L0), was not observed in eoG2^{DSC}.

[ISSN]0370-9361