New Insights from the Oyster Crassostrea rhizophorae on Bivalve Circulating Hemocytes

Abstract

Hemocytes are the first line of defense of the immune system in invertebrates, but despite their important role and enormous potential for the study of gene-environment relationships, research has been impeded by a lack of consensus on their classification. Here we used flow cytometry combined with histological procedures, histochemical reactions and transmission electron microscopy to characterize the hemocytes from the oyster Crassostrea rhizophorae. Transmission electron microscopy revealed remarkable morphological characteristics, such as the presence of membranous cisternae in all mature cells, regardless of size and granulation. Some granular cells contained many cytoplasmic granules that communicated with each other through a network of channels, a feature never previously described for hemocytes. The positive reactions for esterase and acid phosphatase also indicated the presence of mature cells of all sizes and granule contents. Flow cytometry revealed a clear separation in complexity between agranular and granular populations, which could not be differentiated by size, with cells ranging from 2.5 to 25 µm. Based on this evidence we suggest that, at least in C. rhizophorae, the different subpopulations of hemocytes may in reality be different stages of one type of cell, which accumulates granules and loses complexity (with no reduction in size) as it degranulates in the event of an environmental challenge.

Phagocytic activities of hemocytes from the deep-sea symbiotic mussels Bathymodiolus japonicus, B. platifrons, and B. septemdierum

“…In abalone, however, the DNA contents of the blast-like cells were found to be the same as those of the other types of hemocytes, indicating that these cells do not proliferate within the hemolymph [33]. On the contrary, it was suggested that granulocytes differentiate into hyalinocytes via degranulation [13]. Although it is difficult to rule out the possibility that the AGs in the Bathymodiolus mussels are actually blast cells, which differentiate into other types of hemocytes, with or without proliferation, no intermediate type of hemocyte (between the AGs and the granulocytes [EGs and BGs]) was detected in any of the three Bathymodiolus mussels examined in the present study.…”

“…In bivalves, hemocytes are essential for a number of processes, including wound healing, transport and digestion of nutrients, and immune defense [9e13]. Bivalves have two major types of hemocytes: agranular hemocytes, which lack granules, and granular hemocytes, which contain granules [9,12,13]. In mytilid mussels, hemocytes have been classified/characterized using a variety of methods, including density gradient centrifugation [14e16], morphological analysis via light and transmission electron microscopy [14,16e19], and lectin binding assay analyses [19,20].…”

Molecular characterization and expression analysis of purple acid phosphatase gene from pearl oyster Pinctada martensii

“…The molluscan gill, which is the main interface between aquatic organisms and the external environment, is considered to be the first line of defense against bacterial infection (Chen et al, 2011;Lee et al, 2012). In invertebrates, hemocytes function as phagocytes are involved in various host immune responses such as recognition, phagocytosis, encapsulation, and oxidative killing; the hemocytes contain many types of immune factors and endogenous enzymes (Rebelo et al, 2013). This high expression of pm-PAP mRNA in these defense tissues suggest that pm-PAP may have specific functions in immune defense.…”

The new insights into the oyster antimicrobial defense: Cellular, molecular and genetic view

“…From works in the different oyster species, some authors reported basophile and eosinophile granulocytes similar to their mammalian counterparts [16]. Other authors have drawn hypothesis of a cell maturation process in one single lineage from blast-like cells, hyalinocytes to granulocytes [20]. Hence the different hypotheses range from one unique lineage to numerous functionally distinct cell types from different lineages [16,20].…”

“…Other authors have drawn hypothesis of a cell maturation process in one single lineage from blast-like cells, hyalinocytes to granulocytes [20]. Hence the different hypotheses range from one unique lineage to numerous functionally distinct cell types from different lineages [16,20]. One caveat for most of these different reports is that most of the tools that have been used so far for hemocyte characterization were developed to analyze mammals blood cells (like the MGG staining for example) and thus have to be interpreted with caution in other species.…”