Eissenberg L G, West J L, Woods J P, Goldman W E
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Infect Immun. 1991 May;59(5):1639-46. doi: 10.1128/iai.59.5.1639-1646.1991.
We evaluated P388D1 macrophagelike cells as model host cells for studying the intracellular survival and strain-specific virulence of Histoplasma capsulatum. Previously characterized strains which were virulent for mice destroyed monolayers of these cells within a few days. In contrast, related avirulent "smooth" variants failed to do so even after 20 days, although they persisted within P388D1 cells for at least 7 days. On the basis of this observation, we developed a quantitative radiolabel assay to use as an initial screen for virulence. Another cell type lining the respiratory tract was then examined as a potential host for H. capsulatum. Hamster trachea epithelial (HTE) cells readily internalized a variety of strains lacking alpha-(1,3)-glucan in their cell walls; however, the tracheal cells were only rarely infected by organisms possessing this polysaccharide. We subsequently inoculated HTE cells with alpha-(1,3)-glucan-positive strains and enriched for the few yeasts infecting these cells. The progeny resembled smooth variants in terms of colony morphology, the absence of alpha-(1,3)-glucan in their cell walls, and their inability to kill macrophages. Did the HTE cells select for these variant yeasts from the parent inoculum or instigate a change from the parental phenotype? Following a 3-h uptake period, only 2% of the ingested yeasts lacked alpha-(1,3)-glucan. One day later, nearly half of the intracellular organisms lacked this polymer. This rapid conversion of a large proportion of the inoculum suggests some type of environmentally triggered change, perhaps analogous to phase variation seen in many other pathogens. Infection of epithelial cells or some other nonprofessional phagocyte during natural histoplasmosis might give rise to similar variants, thus establishing a reservoir of organisms capable of causing chronic or latent infections.
我们评估了P388D1巨噬样细胞作为模型宿主细胞，用于研究荚膜组织胞浆菌的细胞内存活情况和菌株特异性毒力。先前已鉴定出对小鼠具有毒力的菌株，可在数天内破坏这些细胞的单层。相比之下，相关的无毒“光滑”变体即使在20天后也未能做到这一点，尽管它们在P388D1细胞内存活至少7天。基于这一观察结果，我们开发了一种定量放射性标记测定法，用作毒力的初步筛选。然后，我们检查了呼吸道的另一种细胞类型，作为荚膜组织胞浆菌的潜在宿主。仓鼠气管上皮（HTE）细胞很容易内化多种细胞壁中缺乏α-(1,3)-葡聚糖的菌株；然而，气管细胞很少被具有这种多糖的生物体感染。我们随后用α-(1,3)-葡聚糖阳性菌株接种HTE细胞，并富集感染这些细胞的少数酵母。这些后代在菌落形态、细胞壁中缺乏α-(1,3)-葡聚糖以及无法杀死巨噬细胞方面类似于光滑变体。HTE细胞是从亲本接种物中选择了这些变体酵母，还是引发了亲本表型的变化？在3小时的摄取期后，只有2%的摄入酵母缺乏α-(1,3)-葡聚糖。一天后，几乎一半的细胞内生物体缺乏这种聚合物。接种物中很大一部分的这种快速转变表明存在某种类型的环境触发变化，可能类似于许多其他病原体中观察到的相变。在自然组织胞浆菌病期间，上皮细胞或其他一些非专职吞噬细胞的感染可能会产生类似的变体，从而建立起能够引起慢性或潜伏感染的生物体库。
