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.
Parisi
Maria-Giovanna
MG
Ecosystèmes Lagunaires UMR5119, Université Montpellier 2, cc093, place E. Bataillon, F-34095 Montpellier cedex 05, France.
Li
Hui
H
Jouvet
Lionel B P
LB
Dyrynda
Elisabeth A
EA
Parrinello
Nicolo
N
Cammarata
Matteo
M
Roch
Philippe
P
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*