Blood samples were collected through the caudal vein from
1 fish tank1 using a 1 ml syringe at days 7, 14, and 28 post-feeding.
They were immediately withdrawn into the Eppendorf tubes
without anticoagulant. Blood samples were then allowed to clot
(1 h at room temperature and 4 h at 4 C) and centrifuged at
1500 g, 5 min, and 4 C. The serum was finally collected and
stored at minus 20 C until assay.
Leukocytes isolates from peripheral blood were taken using a
method modified from Ref. [26]. 1 ml of the collected bloods from
1 fish tank1 was diluted with 2 ml of RPMI 1640 (Gibthai). It was
then carefully laid onto 3 ml of Histopaque (Sigma) in a 15 ml tube.
The tube was centrifuged at 400 g for 30 min at room temperature.
After centrifugation, a white buffy coat of leukocytes cells floatedon the top of the Histopaque. Opaque interfaces were carefully
aspirated with a Pasteur pipette and transferred into a clean 15 ml
tube. Phosphate buffer solution (PBS) was then added to attain 6ml
and gently mixed by aspiration. It was centrifuged at 250 g for
10 min. This washing step was repeated 3 times to remove any
residual Histopaque. The isolated leukocytes cells were then resuspended
in the PBS and adjusted to the required cell numbers
for phagocytosis and respiratory activities.