Growth and Immunologic Studies on the Culture Forms of Trypanosoma lewisi *

SYNOPSIS. Culture forms of Trypanosoma lewisi grown at 27 C in a diphasic blood agar medium resemble in structure the stage found in the invertebrate host. Cultures inoculated with approximately 1 × 10 6 trypanosomes/ml attain maximum populations of 2–7 × 10 7 organisms/ml after 5–6 days of incubation. The stationary phase persists 6–15 days. The decline of the population is of relatively long duration with approximately 1 × 10 6 viable organisms/ml present after 90 days. Variations in growth were attributed to the preparation of defibrinated heated rabbit blood incorporated into the culture medium. With inocula of 3.0 × 10 5 trypanosomes/ml there was a lag in growth not observed with larger inocula. Trypanosomes incubated at elevated temperatures had altered growth curves compared to organisms at 27 C. Agitation of cultures did not affect the growth or stationary phases, but hastened the population decline. Heated and unheated 5% (v/v) normal rat serum incorporated in the liquid phase of the medium altered the growth of the organisms. Heated serum caused a decrease in the population and an extended lag phase. The effects on growth were more marked with unheated serum suggesting that both heat‐stable and labile components affect growth. Antisera from rats injected with live culture forms included in the liquid phase inhibited, while antisera from rats 24 days after infection with the blood stream forms had no effect on the growth of the culture forms. Antisera from rabbits immunized with sonicates of culture forms also altered the growth of the organisms in culture. Rabbit antisera prepared by immunization with sonicates of dividing and non‐dividing blood stream forms had no effect on the in vitro growth. Antisera from animals immunized with rat blood and culture medium were also without effect. The immunologic implications of the data are considered and discussed.