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.