Mouse serum as an environment for the growth of Trypanosoma lewisi

Trypanosoma lewisi grows abundantly in the rat, but little or not at all in other rodents. The mouse is especially refractory. In vitro studies revealed no immediate lytic phenomenon in mouse serum, although trypanosomes were more stable over longer periods in rat serum. Early divisions were not inhibited in mouse serum as measured by the technique developed by D'Alesandro (1962). In dialysis bags implanted in the mouse peritoneum, trypanosomes in mouse serum showed only slight multiplication at the best. However, when implanted in diffusion chambers, the trypanosomes grew well, although somewhat irregularly. Trypanosomes were carried through seven once-weekly transfers in mice while enclosed in such chambers. It was possible to hyperimmunize mice against trypanosomes, so that growth in the chambers was inhibited. Furthermore exogenous rat serum injected into the peritoneum produced a great stimulus to growth, while mouse serum showed no further effect. A number of nonrodent sera (human, monkey, dog, cow, newborn calf, horse, and chicken) and "nonspecific" substances (egg albumin, trypticase soy broth, a copolypeptide of glutamic acid and lysine, polyvinyl pyrollidone, dextran, and zymosan) generally failed to demonstrate growth stimulation of T. lewisi in the mouse. Human and monkey sera, however, constituted exceptions. Mouse serum injected into gerbils and rats increased the level of parasitemia. The ability of T. lewisi to grow in mouse serum in the protected environment of the diffusion chamber implies that a total deficiency of nutrients does not occur in the refractory host. If one then assumes only a quantitative nutritional basis for the differences in the growth of T. lewisi in various rodents, a problem arises in explaining the action of mouse serum on increasing parasitemias in the rat and gerbil. Therefore, aspects of both nutrition and defense are probably altered by the heterologous sera supplements.