The penetrative ability of sleeping-sickness trypanosomes

653 TRANSACTIONS OF THE ROYAL SOCIETY OF .TROPICAL MEDICINE AND HYGIENE, VOL. 72, No. 6, 1978

The penetrative

Department

of Medical

ability

Protozoology,

of sleeping-sickness

trypanosomes

D. A. EVANS AND D. S. ELLIS London School of Hygiene and Tropical London WClE 7HT

When we first reported sleeping-sickness trypanosomes within tsetse midgut cells (EVANS & ELLIS 1975), some workers suggested that these might have been merely ‘trapped’ somehow within the gut walls as a result of the great changes in shape that occur in these epithelial cells during ingestion and digestion of the blood-meal and the accompanying peristalsis, no active penetration being required. Recent work on other aspects of the life-cycle of Trypanosoma brucei rhodesiense within Glossina morsitans morsitans has used whole gut-organculture preparations, maintained at 27°C in RPM1 tissue-culture medium with 20% (v/v) foetal calf serum in contact with trypanosomes for seven days. The guts were fixed and processed at intervals for electron microscopy, using the trypanosome stock and techniques already outlined (EVANS & ELLIS) 1975). Plate 1 shows the trypanosomes lying next to the midgut basement membrane in a preparation from an intact tsetse fly 21 days after infection, and was recorded during the original experiments mentioned in the first paragraph. Plate 2 shows trypanosomes having reached exactly the same position in a gut-organ-culture preparation seven days after infection with cultured procyclic trypanosomes, the trypanosomes having probably by-passed the disturbed peritrophic

Medicine,

Keppel

Street,

membrane and entered the cells direcdy (ELLIS & EVANS, 1977). Plate 3 shows trypanosomes on the sixth day after infection within the midgut cells of the gut-organculture, en route to the basement membrane. This finding of trypanosomes within midgut cells of whole inactive gut-organ-cultures of G. morsitans must surely disallow any ‘trapping’ theory, and the absence of host-cell membrane around the intracellular trypanosomes, as first reported (EVANS & ELLIS, 1975) from the intact tsetse, would suggest active penetration and passage across the cells rather than passive uptake. References Ellis, D. S. & Evans, D. A. (1977). Passage of Trypanosoma brucei rhodesiense through the peritrophic membrane of Glossina morsitans moristans. Nature, 267, 834-835. Evans, D. A. & Ellis, D. S. (1975). Penetration of midgut cells of Glossina morsitans morsitans by Trypanosome brucei rhodesiense. Nature, 258, 231-233.

Accepted for publication

3rd May, 1978.

654

PENETRATIVE

ABILITY

OF SLEEPING-SICKNESS

TRYPANOSOMES

PZate 1. x 6,750. Two trypanosomes (arrowed) lying between the intact tsetse mid-gut cell plasmalemma (marked with small arrows) and the basement membrane. The haemocoelomic cavity is labelled ‘H’ and epithelial microvilli ‘M’.

Plate 2~. x 3,600. Two trypanosomes (arrowed) lying beneath the tsetse mid-gut cells’ basement Above the basement membrane membrane of a whole gut culture preparation, 7 days after infection. can be seen the muscle layers surrounding the outer surface of the gut.

Plate 26. x 9,450. An enlargement plasmalemma is arrowed.

of the right

hand trypanosome

in Plate 2a. The gut epithelial

Plate 3. x 4,800. A similar preparation to Plate 2, 6 days after infection, within the tsetse mid-gut cells. The microvilli are marked ‘M’.

with

trypanosomes

cell

(arrowed)

D. A. EVANS

AND

D.

S. ELLIS

655