DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY, Vol. 12, pp. 495-507, 1988 0145-305X/88 $3.00 + .00 Printed in the USA Copyright (c) 1988 Pergamon Press plc All rights reserved D-GALACTOSE BINDING LECTINS FROM THE TUNICATE ASCIDIA MALACA: SUBUNIT CHARACTERIZATION AND HEMOCYTE SURFACE DISTRIBUTION Nicol6 Parrinello and Vincenzo Arizza Institute of Zoology University of Palermo via Archirafi 18 90123 Palermo ITALY ABSTRACT D-galactose specific lectins purified from Ascidia malaca serum contain a major protein component with an apparent molecular weight of about 58,000 daltons, which moves more rapidly under non-reducing condit- ions. Intramolecular disulfide linkages can explain this behaviour, suggesting a compact protein struc- ture. Membrane lectins have been demonstrated on the surface of about 34% hemocytes by immunofluorescent methods using a rabbit antiserum against the isolated serum lectins. Small, medium and large hemocytes can be positive, as also shown by binding on Sepharose spherules or by rosette formation ~-~ith sheep and rabbit erythrocytes. Binding is inhibited bF the same sugars specific for the serum lect~ns. Finally, antibodies to the serum lectins specifically aggluti- nate the hemocytes. This evidence supports the hypo- thesis that a lectin with the same specificity and certain structural similarities can be found free in the serum and present on hemocyte surfaces. INTRODUCTION Although invertebrates possess self non-self ,-ecognition systems, they do not produce immunoglobulins, and the nat~re of their recognition structures cannot be defined in terms of specific antibody-antigen complementarity (I, 2). Studies of 495