Infectivity and Attenuation of Leishmania donovani Promastigotes: Association of Galactosyl Transferase with Loss of Parasite Virulence

During the course of long-term in vitro cultivation of Leishmania donovani parasites, the promastigotes were found to lose their infectivity. Lectin agglutination studies revealed that there is an up-regulation of terminally exposed galactose residues on the noninfective promastigotes. The enzyme galactosyl transferase was absent in the infective form but present in the non-infective form of the parasites. An association between galactosylation and loss of infectivity was also observed. We propose that the enzyme galactosyl transferase is developmentally regulated and induces galactosylation of surface carbohydrates.