Differences in uptake and killing of pathogenic and non-pathogenic bacteria by haemocyte subpopulations of penaeid shrimp, Litopenaeus vannamei, (Boone)

摘要

Phagocytosis is an important function of both invertebrate and vertebrate blood cells. In this study, the phagocytic activity of haemocyte subpopulations of penaeid shrimp, Litopenaeus vannamei, (Boone), against pathogenic and nonpathogenic particles was investigated in vitro. The haemocytes of penaeid shrimp were firstly separated by centrifugation on a continuous density gradient of iodixanol into four fractions with five subpopulations (sub), of which sub 1 (hyalinocytes) and sub 4 (semi-granulocytes) have the main function in phagocytosis of both pathogenic and non-pathogenic bacteria as well as fluorescent polystyrene beads. It was found that these haemocyte subpopulations engulfed virulent Vibrio campbellii and Vibrio harveyi at a higher rate than nonvirulent Escherichia coli and polystyrene beads. When these bacteria were mixed with shrimp haemocyte subpopulations and incubated for 180 min, the percentage of viable intracellular V. campbellii (25.5 +/- 6.0%) recovered was significantly higher than the percentage recovered from V. harveyi (13.5 +/- 1.1%). No viable intracellular E. coli was observed in this study. In contrast to V. harveyi and E. coli, V. campbellii containing endosomes did not acidify in time. Incubation of haemocyte subpopulations with the most virulent V. campbellii strain resulted in a significant drop in haemocyte viability (41.4 +/- 6.3% in sub 1 and 30.2 +/- 15.1% in sub 4) after 180 min post-inoculation in comparison with the less virulent V. harveyi (84.1 +/- 5.6% in sub 1 and 83.4 +/- 4.1% in sub 4) and non-virulent E. coli (92.7 +/- 2.8% in sub 1 and 92.3 +/- 5.6% in sub 4) and polystyrene beads (91.9 +/- 1.6% in sub 1 and 84.4 +/- 3.4% in sub 4). These findings may be a valuable tool for monitoring shrimp health and immunological studies.