Humanized nonobese diabetic-scid IL2rgammanull mice are susceptible to lethal Salmonella Typhi infection

Abstract

Salmonella enterica serovar Typhi, the cause of typhoid fever, is host-adapted to humans and unable to cause disease in mice. Here, we show that S. Typhi can replicate in vivo in nonobese diabetic (NOD)-scid IL2rgamma(null) mice engrafted with human hematopoietic stem cells (hu-SRC-SCID mice) to cause a lethal infection with pathological and inflammatory cytokine responses resembling human typhoid. In contrast, S. Typhi does not exhibit net replication or cause illness in nonengrafted or immunocompetent control animals. Screening of transposon pools in hu-SRC-SCID mice revealed both known and previously unknown Salmonella virulence determinants, including Salmonella Pathogenicity Islands 1, 2, 3, 4, and 6. Our observations indicate that the presence of human immune cells allows the in vivo replication of S. Typhi in mice. The hu-SRC-SCID mouse provides an unprecedented opportunity to gain insights into S. Typhi pathogenesis and devise strategies for the prevention of typhoid fever.

Fig. 1.

S. Typhi virulence in hu-SRC-SCID Mice. (A) Survival of engrafted hu-SRC-SCID mice after i.p. injection of 5.5 × 10⁴–3.2 × 10⁵ cfu (low, n = 11) or 3 × 10⁶ cfu (high, n = 8). S. Typhi Ty2 is shown as a Kaplan–Meier plot. Survival is compared with that of parental nonengrafted NOD-scid IL2rγ^null (n = 6) or immunocompetent NOD^+/+ (n = 6) mice receiving i.p. injection of 5.5 × 10⁴–1.8 × 10⁵ cfu. Aggregate data include mice receiving Ty2 and Ty2-derived transposon pools. (B) Organism burden was quantified in livers and spleens of nonengrafted NOD-scid IL2rγ^null and engrafted hu-SRC-SCID mice 48 h after i.p. inoculation of 1–3 × 10⁵ cfu S. Typhi Ty2. Horizontal lines indicate medians. Asterisk denotes significant difference by Wilcoxon rank-sum test.

Fig. 2.

Pathology of typhoid in hu-SRC-SCID mice. (A) Granulomatous inflammation with mononuclear cell infiltration in the spleen of an infected hu-SRC-SCID mouse after 48–72 h. (B) Multinucleated giant cell (arrow) in the spleen of an infected hu-SRC-SCID mouse. (C) Central lobular hepatocellular changes in the liver of an infected hu-SRC-SCID mouse. (D) Kupffer cell swelling (arrow) in the liver of an infected hu-SRC-SCID mouse. (E) Mild hepatocellular changes with normal-appearing Kupffer cells (arrow) in the liver of an infected control NOD-scid IL2rγ^null mouse. (F) Pyknotic lymphocytes (arrow) with cytoplasmic shrinkage in the spleen of an infected hu-SRC-SCID mouse. (G) Low background levels of cell death (arrow) visualized by TUNEL straining in the spleen of an infected control NOD-scid IL2rγ^null mouse. (H) Increased cell death (arrows) visualized by TUNEL staining in the spleen of an infected hu-SRC-SCID mouse. (Magnification: A, 100×; B–H, 400×; scale bar: A, 100 μm; B–H, 10 μm.)

Fig. 3.

Visualization of human CD45⁺ cells in infected hu-SRC-SCID mice. Sections were obtained from NOD-scid IL2rγ^null or hu-SRC-SCID mice infected as in Fig. 2 and strained with H&E (Left). Engrafted hematopoietic cells expressing human CD45 are stained brown and counterstained with hematoxylin (Right).

Fig. 4.

Serum cytokine levels in S. Typhi-infected hu-SRC-SCID mice. Serum concentrations of murine (M) and human (H) IL-6, IL-10, MCP-1, IFNγ, TNFα, and IL12p70 were assayed by cytometric bead array in nonengrafted NOD-scid IL2rγ^null or engrafted hu-SRC-SCID mice 56–72 h after infection with S. Typhi Ty2 (n = 5 per group, error bars = SEM).