Giannini M S
J Parasitol. 1987 Feb;73(1):144-8.
To test the hypothesis that the rapid immune response of rats to Trypanosoma lewisi is elicited by prior exposure to cross-reacting environmental antigens, the early immune response to infection with this nonpathogenic protozoan was studied in germ-free and conventional rats. In germ-free rats, initial levels of both IgG and IgM were significantly lower than those of conventional rats. After infection, the germ-free rats made more immunoglobulins of both classes, and made them more quickly, than did conventional rats. Trypanosome-specific antibodies appeared earlier and in higher titers in the germ-free rats. Because they lacked intestinal microflora, it is unlikely that the germ-free rats' responses had been primed; thus, these observations indicated that the conventional rats' responses to some trypanosome antigens had been down-regulated by their prior exposure to environmental antigens. However, protective antibodies that inhibited parasite reproduction (ablastin) may have been primed, because these appeared in sera 2 days earlier in conventional rats. Despite much lower rates of production of trypanosome-specific antibodies, the conventional rats had the same peak parasitemias and times to crisis as germ-free rats. Thus it is apparent that protective immunity to this nonpathogenic parasite is not down-regulated by prior exposure to environmental antigens, as would be predicted.
为了验证大鼠对鲁氏锥虫的快速免疫反应是由先前接触交叉反应性环境抗原所引发这一假说，在无菌大鼠和普通大鼠中研究了它们对这种非致病性原生动物感染的早期免疫反应。在无菌大鼠中，IgG和IgM的初始水平均显著低于普通大鼠。感染后，无菌大鼠产生的这两类免疫球蛋白都比普通大鼠更多，且产生速度更快。锥虫特异性抗体在无菌大鼠中出现得更早，且滴度更高。由于无菌大鼠缺乏肠道微生物群，它们的反应不太可能是由先前致敏引起的；因此，这些观察结果表明，普通大鼠对某些锥虫抗原的反应因先前接触环境抗原而受到下调。然而，抑制寄生虫繁殖的保护性抗体（抑殖素）可能已经被致敏，因为在普通大鼠的血清中这些抗体出现的时间要早两天。尽管锥虫特异性抗体的产生率要低得多，但普通大鼠的寄生虫血症峰值和达到危机的时间与无菌大鼠相同。因此，很明显，对这种非致病性寄生虫的保护性免疫并未如预期那样因先前接触环境抗原而受到下调。
