The significance of the amoebocyte-producing organ in Biomphalaria glabrata

Abstract

In molluscs, internal defence against microorganisms is performed by a single cell type, i.e., the haemocyte or amoebocyte. The origin of these cells in Biomphalaria glabrata was initially thought to be localised within the vasculo-connective tissue. More recently, origin from a single organ, termed the amoebocyte-producing organ (APO), has been postulated based on the occurrence of hyperplasia and mitoses during Schistosoma mansoni infection. The present investigation represents a histological, immuno-histochemical and ultra-structural study of the B. glabrata APO, whereby histological identification was facilitated by means of collecting epithelial basophilic cells. These cells were comprised of single-cell layers that cover a portion of the stroma, which contains many small, round cells and haemolymph sinuses, as well as a small area of the pericardial surface of the reno-pericardial region. On occasion, this epithelial component vaguely resembled the vertebrate juxtaglomerular apparatus, which reinforces its presumed relationship to the kidney. Both in normal and infected molluscs, mitoses were only occasionally found. The present quantitative studies failed to demonstrate the presence of APO cellular hyperplasia, either in normal or schistosome-infected B. glabrata. Conversely, several structural details from the APO region in B. glabrata were found to be consistent with the hypothesis that the APO is a filtration organ, i.e., it is more closely related to the kidney rather than the bone marrow, as has been suggested in the literature.

Ultrastructural characterization of cells in primary cultures from different adult tissues of Biomphalaria tenagophila TAIM, a strain that is absolutely resistant to Schistosoma mansoni infection

“…Unfortunately, as morphological data on these particular cells are not available, comparison with those obtained herein was not possible. Indeed, the similarities between APO and SK cultures, their anatomical proximity in the Biomphalaria body, and partial hemoblast characteristics presented by SK cells suggest that the SK tissue may participate in hemocyte production [Souza and Andrade, 2012;Pan, 1958]. Despite the previously reported differences between SK and APO cells [Sullivan and Spence, 1999;Andrade, 2006, 2012], bright field microscopy performed here revealed that they are very similar in organ-derived cultures [Barbosa et al, 2006b].…”

Haematopoiesis in molluscs: A review of haemocyte development and function in gastropods, cephalopods and bivalves

“…Souza and Andrade (2006, 2012) [63, 64] have proposed an alternative function for the APO in B. glabrata , i.e., renal absorption and filtration. This hypothesis is based in part on ultrastructural observations that there are no “transitional forms” between mantle epithelial cells and haemocytes [64], and that the APO “vaguely resembled the juxtaglomerular apparatus” of the vertebrate kidney [63].…”

“…This hypothesis is based in part on ultrastructural observations that there are no “transitional forms” between mantle epithelial cells and haemocytes [64], and that the APO “vaguely resembled the juxtaglomerular apparatus” of the vertebrate kidney [63]. However, although haemocyte progenitor cells have been reported from oyster gill epithelium [21], we are not aware of any reports of mantle epithelial cells differentiating into haemocytes, and, therefore, transitional cells would not be expected.…”

Destruction of secondary Schistosoma mansoni sporocysts in Biomphalaria glabrata after phytochemical exposure

“…For cell counting, 10 µl of the hemolymph was diluted (1:1) in saline buffer (18 g L − 1 D-glucose, 12.2 g L − 1 KCl, 0.6 gL − 1 NaHCo3, 380 mOsm, pH 7.8) [24]. The number of total circulating hemocytes was determined by direct observation in a hemocytometer chamber by phase-contrast optical microscopy [25]. The hemocytes were characterized according to Cavalcanti et al [26].…”