Infectivity and attenuation of Leishmania donovani promastigotes. II: Association of the loss of parasite infectivity with the terminal galactosylation of precursor acceptors present in virulent parasites by the developmentally regulated galactosyltransferase.

The beta1-4 galactosyltransferase enzyme of the Leishmania donovani promastigotes, was found to be developmentally regulated and expressed only in the attenuated parasites. The enzymatic product of soluble determinants of virulent promastigotes and the galactosyltransferase enzyme was found to stimulate the macrophage burst activity but inhibit in vitro intracellular parasitism. In contrast, removal of terminal galactose moieties from soluble determinants of attenuated parasites resulted in the inhibition of macrophage respiratory burst activity but did not now inhibit intracellular parasitism. We propose that the terminal galactosylation of acceptor substrates present in virulent parasites by the developmentally regulated galactosyltransferase is associated with loss of parasite virulence.