2.7.2. Preparation of leukocytes
The leukocytes were isolated from the peripheral blood by the following
method modified from MacArtain et al. (2007). About 0.5 ml of
blood was collected from each fish, diluted with 2 ml of RPMI 1640
(Gibthai) and then was carefully laid onto 3 ml of Histopaque (Sigma)
in a 15 ml tube; the tubes were centrifuged at 400 × g for 30 min at
RT. After centrifugation, the white fluffy coat of leukocytes floated on
the top of the Histopaque. The opaque interfaces were carefully aspirated
with a Pasteur pipette and transferred into a clean 15 ml tube. The
PBS was added in each tube to attain 6 ml and gently mixed by aspiration,
centrifuged at 250 × g for 10 min. This washing step was repeated
three times to remove any residue of Histopaque. The isolated leukocytes
cells were then re-suspended in the PBS and adjusted to the required
cell numbers to study the phagocytosis and respiratory burst
activities.