Identification of antigenically distinct hemocyte subpopulations in Biomphalaria glabrata (Gastropoda) using monoclonal antibodies to surface membrane markers.

Five monoclonal antibodies (mABs) against surface antigens on circulating, glass-adherent hemocytes of the snail, Biomphalaria glabrata, were produced by somatic cell hybridization methods. Two mABs (IID2.6-Bg and IID4.8-Bg) are pan-hemocytic, reacting uniformly with epitopes shared by all adherent hemocytes. Determinants recognized by these mABs also are present in soluble form and appear to be associated with a hemoglobin-depleted ultracentrifuged fraction of snail hemolymph. Hybridoma-derived mABs IIC6.8-Bg and VB10.3-Bg recognize hemocyte surface epitopes expressed by only 50-60% of the adherent cell population. These mABs also are reactive with soluble hemolymph antigens but apparently recognize determinants which are different from the IID2.6-Bg and IID4.8-Bg reactive sites. Another antigenically distinct hemocyte subpopulation is recognized by mAB IID7.1-Bg. Epitopes that are reactive with this mAB differ from the previously described determinants by their asymmetrical distribution on the surface of positive cells and the absence of soluble antigenic components in hemolymph. Furthermore, unlike the other mABs, the prevalence of hemocytes staining with IID7.1-Bg antibodies differed between two strains of B. glabrata. Results of this study clearly demonstrate that circulating B. glabrata hemocytes, consisting of a single, predominant population of adherent cells, is composed of several distinct antigenic subpopulations based on the specific binding of anti-hemocyte mAB probes. Our successful application of hybridoma techniques to the study of molluscan hemocyte surface antigens underscores further the great potential usefulness of this method in analysing the molecular basis of hemocyte reactivity.