1564 Surface Antigens of Leishmania Donovani Promastigotes

Leishmania donovani, the agent of visceral leishmaniasis , is a t r y p a n o s o m a t i d protozoan t r ansmi t t ed by ph leboto in ine sandflies. The paras i te cycles between a nonmot i le , in t race l lu la r amast igote stage paras i t iz ing the mononuc lea r phagocytes of the mammal ian host and an extracel lular , moti le p romas t igo te stage in the insect vector, A s imilar p romas t igo te form develops when parasi tes are cu l tu red in cell-free m e d i u m at 26-28°C (1) and remains infective when injected into susceptible hosts (2). In humans , L. donovani produces a range of disease states (3). T h e classic ka la -azar of I n d i a is a disease of adul ts wi th no known an imal reservoir and associat ion with pos t -ka la -azar dermal lesions. Sudanese ka la -azar also affects adults , bu t shows li t t le t endency toward de rmal sequelae, some he ightened resistance to an t imony t rea tment , and has its na tu ra l reservoir in the rat. Lastly, the M e d i t e r r a ne a n and South Amer ican var iants are diseases of ch i ldhood with dogs as f requent reservoirs. Efforts to correlate these cl inical and epidemiologica l manifes ta t ions wi th specific Leishmania donovani strains and isolates have led to numerous classification schemes. These depend upon compar isons of D N A buoyan t densi ty (4), e lec t rophoret ic pa t te rns of isoenzymes (5, 6), serologic methods di rec ted at excreted factors (7), and examina t ion of the surface prote ins of cu l tu red parasi tes (8). To date, none has been successful in ident i fy ing ant igens c o m m o n to all or a c l inical ly significant subset of L. donovani isolates. In this paper , we report that the surface ant igen profiles of Leishmania donovani promas t igo te isolates from Brazil and Africa are r emarkab ly s imilar and ex t remely simple. A glycoprote in of 65,000 mol wt is the pr inc ipa l componen t ident i f ied by bo th surface iod ina t ion and biosynthet ic labeling. Recogni t ion of this 65,000 mol wt g lycopept ide by h u m a n i m m u n e sera from diverse geographic locations establishes it as a ma jo r immunogen ic de t e rminan t common in at least two cl inical var iants of leishmaniasis .