Adhesion-blocking antibodies prepared against gp150 react with gp80 of Dictyostelium.

A membrane glycoprotein of 150 000 D, gp150, has been implicated in the mechanism of cell-cell adhesion which arises during development of Dictyostelium discoideum. This conclusion was founded on the observation that monovalent Fab' fragments prepared from an antiserum raised against partially purified gp150 are able to block cell-cell adhesion. We show that this serum contains antibodies to a distinct membrane glycoprotein, gp80, previously implicated in cell-cell adhesion. Reaction of Fab' to this surface molecule can account for the adhesion-blocking activity in the antiserum to gp 150. Moreover, binding of gp80 neutralized Fab' to gp150 does not block adhesion. If gp150 carries other determinants which bind adhesion-blocking Fab', these determinants must also be present on gp80. Thus, it is not clear that gp150 is directly involved in cell-cell adhesion of Dictyostelium.