Yersinia pestis YopJ suppresses tumor necrosis factor alpha induction and contributes to apoptosis of immune cells in the lymph node but is not required for virulence in a rat model of bubonic plague

Abstract

The virulence of the pathogenic Yersinia species depends on a plasmid-encoded type III secretion system that transfers six Yop effector proteins into host cells. One of these proteins, YopJ, has been shown to disrupt host cell signaling pathways involved in proinflammatory cytokine production and to induce macrophage apoptosis in vitro. YopJ-dependent apoptosis in mesenteric lymph nodes has also been demonstrated in a mouse model of Yersinia pseudotuberculosis infection. These results suggest that YopJ attenuates the host innate and adaptive immune response during infection, but the role of YopJ during bubonic plague has not been completely established. We evaluated the role of Yersinia pestis YopJ in a rat model of bubonic plague following intradermal infection with a fully virulent Y. pestis strain and an isogenic yopJ mutant. Deletion of yopJ resulted in a twofold decrease in the number of apoptotic immune cells in the bubo and a threefold increase in serum tumor necrosis factor alpha levels but did not result in decreased virulence, systemic spread, or colonization levels in the spleen and blood. Our results indicate that YopJ is not essential for bubonic plague pathogenesis, even after peripheral inoculation of low doses of Y. pestis. Instead, the effects of YopJ appear to overlap and augment the immunomodulatory effects of other Y. pestis virulence factors.

FIG. 1.

Incidence of terminal plague in Brown Norway rats following intradermal injection of 100 CFU (A), 10 CFU (B), or ∼1 CFU (C) of wild-type (solid squares) or ΔyopJ (open circles) Y. pestis. The calculated LD₅₀ of both strains is <10 CFU.

FIG. 2.

Identical histopathologies produced by wild-type and ΔyopJ Y. pestis. Hematoxylin-and-eosin-stained sections of spleens (A to D) and inguinal buboes (E to H) from rats infected with wild-type (left column) or ΔyopJ (right column) Y. pestis were examined. The arrowheads indicate large aggregates of extracellular bacteria. P, periarterial lymphatic sheath. Original magnifications, ×200 (A and B), ×600 (C and D), ×10 (E and F), and ×400 (G and H).

FIG. 3.

Colonization in the spleen (A) and blood (B) in rats inoculated intradermally with ∼1, 10, 100, or 1,000 CFU wild-type Y. pestis (solid circles) or ΔyopJ Y. pestis (open circles). Each symbol indicates the bacterial load in a single rat at the terminal stage of plague; the horizontal lines indicate the mean log CFU per gram of spleen or milliliter of blood.