Differential involvement of mussel hemocyte sub-populations in the clearance of bacteria.
Mussels are filter-feeders living in a bacteria-rich environment. We have previously found that numerous bacterial species are naturally present within the cell-free hemolymph, including several of the Vibrio genus, whereas the intra-cellular content of hemocytes was sterile. When bacteria were injected into the circulation of the mussel, the number of living intra-hemocyte bacteria dramatically increased in less than an hour, suggesting intense phagocytosis, then gradually decreased, with no viable bacteria remaining 12h post-injection for Micrococcus lysodeikticus, 24h for Vibrio splendidus and more than 48 h for Vibrio anguillarum. The total hemocyte count (THC) was dramatically lowered by the bacterial injections, as quantified by flow cytometry. V. splendidus induced the strongest decreases with -66% 9h post-injection of living bacteria and -56% 3h post-injection of heat-killed bacteria. Flow cytometry was used to identify three main sub-populations of hemocytes, namely hyalinocytes, small granulocytes and large granulocytes. When THC was minimal, i.e. within the first 9h post-injection, proportions of the three cell categories varied dramatically, suggesting differential involvement according to the targets, but small granulocytes remained the majority. According to a decrease in their number followed by an increase (+90% at 12h with living V. splendidus), hyalinocytes also appeared to be involved as cellular effectors of antibacterial immunity, despite possessing little capacity for phagocytosis and not containing antimicrobial peptides.
Ecosystèmes Lagunaires UMR5119, Université Montpellier 2, cc093, place E. Bataillon, F-34095 Montpellier cedex 05, France.
Maria-Giovanna
MG
Parisi
Hui
H
Li
Lionel B P
LB
Jouvet
Elisabeth A
EA
Dyrynda
Nicolo
N
Parrinello
Matteo
M
Cammarata
Philippe
P
Roch
D000818:Animals; D015169:Colony Count, Microbial / Q000662:veterinary; D005434:Flow Cytometry / Q000662:veterinary; D016908:Gram-Positive Bacterial Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D006434:Hemocytes / Q000276:immunology / Q000382:microbiology; D006458:Hemolymph / Q000166:cytology / Q000276:immunology / Q000382:microbiology*; D008837:Micrococcus / Q000276:immunology*; D049878:Mytilus / Q000276:immunology / Q000382:microbiology*; D014733:Vibrio / Q000276:immunology*; D014735:Vibrio Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*