Characterization of molluscan phagocyte subpopulations based on lysosomal enzyme markers

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Abstract
This study quantitatively analyzed the distribution and abundance of the lysosomal enzyme markers, acid phosphatase (AP), nonspecific esterase (NE), and peroxidase (PO) within and between the phagocytes (hemocytes) of two strains of the snail, Biomphalaria. Glabrata, vector host for the human blood fluke, Schistosoma mansoni. Discrete subpopulations of AP‐, NE‐, and PO‐staining cells were found in the glass‐adherent hemocyte population of both schistosome‐resistant (10‐R2) and susceptible (PR albino) strains of the snail. Furthermore, there were significant differences in the distribution and abundance of the different enzymes defining the subpopulations within and between the snail strains. Generally, 10‐R2 hemocytes have a higher enzymatic activity than PR albino cells, which, in part, can be attributed to larger NE‐only, AP‐only, and AP + NE‐staining hemocytes in the 10‐R2 strain, and a larger subpopulation of negative cells in PR albino snails. Moreover, these differences in hemocyte enzyme content are further augmented by the fact that the 10‐R2 strain has nearly twice as many circulating, glass‐adherent blood cells when compared to PR albino snails. These findings may be of additional significance, since previous studies have implicated hemocyte lysosomal enzymes in the killing of schistosome larvae in naturally resistant 10‐R2 snails, although accurate measurements of strain‐specific enzyme levels in these cells have not been conducted. The present study provides direct evidence that 10‐R2 snails naturally possess a much greater lysosomal enzyme content than do those of the PR albino strain, which, in turn, may be related to the observed resistance or susceptibility in these two molluscan strains.
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