Lipopolysaccharide induces DNA-synthesis in a sub-population of hemocytes from the swimming crab, Liocarcinus depurator

Abstract

The swimming crab, Liocarinus depurator, contains a small proportion of circulating blood cells which enter S-phase in vitro, as revealed by BrdU assay. These cells are enriched within the semigranular cell band produced by density gradient centrifugation on Percoll and their proportion is significantly higher in blood samples taken from crabs injected 3h previously with lipopolysaccharide (LPS). The occurrence of these cells does not persist as blood samples taken 12h post-injection show similar numbers of these cells to those from saline-treated and untreated controls. However, their appearance appears to be dose related; hemolymph from animals given 15 microg LPS per animal contains greater numbers than that from animals given LPS doses of 0.15 or 0.015 microg per animal. Estimation of the probable number of these cells per ml of the hemolymph, taking into account cell viability and changes in the size of the semigranular cell pool, indicates that they are very rare, comprising merely ca 0.06% of the total cell count. Notwithstanding, this still represents a baseline population in the region of 1.25 x 10(4) ml-1. More importantly, their number rises, approximately 11-fold to ca 14 x 10(4) ml-1 of hemolymph by 3h of injection of LPS. These results show that certain hemocytes from a brachyuran crab can synthesise DNA in vitro, and offers evidence that these cells constitute a rare but distinct sub-population of hemocytes that co-migrate with the semigranular cells during density gradient centrifugation. Since the cells received the stimulus to enter S-phase in vivo, the response must represent one of the mechanisms used by decapods to restore the hemocyte number in the circulation after non-self challenge.