The expression of an adhesion-related protein by clam hemocytes.

Molluscs have circulating cells in the hemolymph which are both adherent and phagocytic. Mya arenaria, the soft-shell clam, is particularly interesting because it develops a leukemia detected first in the hemolymph and, as the disease progresses, in solid tissue. We have previously described a leukemia-specific protein (Miosky et al., 1989) identified by murine monoclonal antibodies generated to pure populations of leukemia cells. In the following work, a monoclonal antibody was generated to normal hemocytes of Mya. The antibody, designated 2A4, was evaluated by ELISA, immunocytochemistry, Western blotting, and flow cytometry. The 2A4 antigen was detected on 87% normal adherent cells. However, 2A4 was lost as leukemia cells proliferated. The mature leukemia cell, which is nonadherent, neither expresses 2A4 nor can 2A4 be detected in the leukemia cell lystate. Western blot analyses reveal that 2A4 reacts with a 130-kDa protein. Our data suggest that p130 may be involved in the regulation of cell adhesion.

Leukemia cell specific protein of the bivalve mollusc Mya arenaria.

Soft shell clams, Mya arenaria, develop leukemias in the hemolymph which are fatal. Tissue sections and hemolymph samples from normal and tumor-bearing clams were tested with an anti-leukemic cell specific monoclonal antibody (Mab) "IEII." Evaluation of leukemic cells and normal hemocytes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses showed that Mab IEII bound to a large protein of approximately 200 kDa from the tumor cell, but not from the normal cell preparation.

Ontogeny of leukemic cells of the soft shell clam.

A leukemic disease of the soft shell clam, Mya arenaria, has been identified along the east coast of the United States since 1977. This disease, first called hematopoietic neoplasia, is characterized by circulating tumor cells which are found in the hemolymph even before significant tissue invasion or localization of the cells can be demonstrated. The ontogeny of the leukemic cells, however, has not been resolved and remains an area of controversy. Monoclonal antibodies (Mab) developed by our laboratory were screened for specificity against the leukemic cell and normal hemocytes using an indirect immunoperoxidase technique. The method demonstrated that a new Mab "4A9" reacted both with leukemic cells and with a small subpopulation of normal circulating hemocytes (NSC). Mab 4A9 not only stained leukemic cells and NSC in peripheral hemolymph, but, more importantly, reacted specifically with another cell, the "connective tissue cell" (CTC) in clams with leukemia. The data presented in this paper show that Mab 4A9 stains a subset of normal circulating cells, leukemic cells, and the CTCs. These data lead to the hypothesis that the CTC may be the cell of origin for not only the NSC (a normal hemocyte) but also for the leukemic cell.