Lipophosphoglycan and secreted acid phosphatase of Leishmania tropica share species-specific epitopes

Several species-specific monoclonal antibodies (T11, T13-T15) which only react with Leishmania tropica, recognize phosphorylated carbohydrate epitopes on lipophosphoglycan and the structurally related molecule, phosphoglycan, which is shed by promastigotes into spent culture medium. During immunoaffinity isolation of [³²P]orthophosphate-labeled phosphoglycan on monoclonal antibody T15 conjugated to Sepharose 4B, a high-M_r component (approx. 200 000) was co-purified. The latter material is metabolically labeled with [³⁵S]methionine and [³H]glucosamine. This glycoprotein was separated from phosphoglycan by chromatography on lentil lectin resin. The glycoprotein exhibited a l-tartrate-sensitive acid phosphatase activity, typical of secreted acid phosphatase (EC 3.1.3.2) from Leishmania. Monospecific antibodies to Leishmania donovani-secreted acid phosphatase selectively precipitated the L. tropica enzyme from immunoaffinity purified mixtures of the two antigens, and monoclonal antibodies to lipophosphoglycan precipitate the pure enzyme. Species-specific monoclonal antibodies to L. major lipophosphoglycan also recognized both L. tropica antigens. Treatment of the acid phosphatase with periodate or phosphodiesterase I abolished binding by the monoclonal antibodies to the pure enzyme. These results demonstrate that the two major secreted glycoconjugates of Leishmania tropica, the lipophosphoglycan and the acid phosphatase, share species-specific phosphorylated carbohydrate epitope(s).