METACYCLOGENESIS OF LEISHMANIA (VIANNIA) BRAZILIENSIS IN-VITRO - EVIDENCE THAT LENTIL LECTIN IS A MARKER OF COMPLEMENT RESISTANCE AND ENHANCED INFECTIVITY

Axenic culture in modified Grace's medium was used to induce metacyclo genesis of Leishmania (Viannia) braziliensis in vitro. Morphological c haracteristics, lectin agglutination profiles, susceptibility to compl ement lysis, and infectivity in vivo were compared between metacyclic promastigotes and promastigotes in mid-log phase growth. Short, arrow- like promastigotes and round, oval promastigotes were defined as putat ive metacyclic forms on the basis of being highly motile and free swim ming, with a small cell body and long flagellum. These forms increased during metacyclogenesis to >80% whereas long-bodied, slender promasti gotes and intermediate slender promastigotes declined progressively. L entil lectin selectively agglutinated L. braziliensis after the induct ion of metacyclogenesis, whereas concanavalin A, wheat germ agglutinin and peanut agglutinin similarly agglutinated metacyclic promastigotes and mid-log phase promastigotes. Metacyclic promastigotes survived in 7.5%-20% human serum whereas mid-log phase promastigotes did not. Fiv e hundred metacyclic promastigotes were highly infective to hamsters w hereas 500 mid-log phase promastigotes rarely caused any lesion. Speci fic agglutination by lentil lectin should allow purification of metacy clic organisms for standardization of immunoprotection and challenge e xperiments.