Leishmania mexicana mexicana: Attachment and Uptake of Promastigotes to and by Macrophages In Vitro1

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Abstract
Promastigotes of L. m. mexicana attach to mouse macrophages in vitro in the absence of serum by a wheat germ agglutinin-like ligand on the surface of the promastigote that binds to the N-acetyl glucosamine moiety of a receptor on the surface of the macrophage. The binding is temperature dependent, and the macrophage receptor is trypsin, cytochalasin B and glutaraldehyde sensitive. The promastigote ligand is proteolytic enzyme and glutaraldehyde insensitive. Uptake follows attachment and is assisted or inhibited as for attachment. Treatment of promastigotes with proteolytic enzymes uncovers a receptor for a serum component that binds strongly to a mouse macrophage receptor in vitro. The strain of mice donating the macrophages had little effect upon attachment and uptake except that A strain mouse macrophages attached fewer promastigotes in 10 min than those of outbred mice, but took up as many promastigotes over 90 min as those of outbred mice. Low responder Biozzi mouse macrophages took up more promastigotes than high responder Biozzi mouse macrophages. Normal unheated human, rabbit and guinea pig sera lysed promastigotes and so inhibited their attachment to macrophages in vitro. Unheated immune serum showed an enhanced inhibition of attachment. Heated normal serum allowed attachment and uptake, while promastigotes treated with heated immune serum showed enhanced attachment to and uptake by macrophages. Treatment of macrophages in vitro with immune serum enhanced their ability to attach promastigotes and to engulf them. Repeated 90-min exposures of a population of promastigotes to uptake by mouse macrophages in vitro did not deplete the population of any sub-population more likely to be taken by macrophages. The 1st sub-population to be taken up survived better in macrophages over 24 h than subsequently engulfed sub-populations.