The roles of IL-12 and IL-23 in CD8+ T cell-mediated immunity against Listeria monocytogenes: Insights from a DC vaccination model

Abstract

Listeria monocytogenes infection induces a strong inflammatory response characterized by the production of IL-12 and IFN-gamma and protective immunity against this pathogen is dependent on CD8+ T cells (CTL). Recent studies have suggested that these inflammatory cytokines affect the rate of memory CD8+ T cell generation as well as the number of short-lived effector cells generated. The role of the closely related cytokine, IL-23, in this response has not been examined. We hypothesized that IL-12 and IL-23 produced by dendritic cells collectively enhance the generation and function of memory cells. To test this hypothesis, we employed a DC vaccination approach. Mice lacking IL-12 and IL-23 were vaccinated with wild-type (WT), IL-12(-/-), or IL-12/23(-/-) DC and protection to Lm was monitored. Mice vaccinated with WT and IL-12(-/-) DC were resistant to lethal challenge with Lm. Surprisingly, mice vaccinated with IL-12/23(-/-) DC exhibited significantly reduced protection when challenged. Protection correlated with the relative size of the memory pools generated. In summary, these data indicate that IL-23 can partially compensate for the lack of IL-12 in the generation protective immunity against Lm.

Fig. 1

Survival of lethal Lm challenge is augmented by IL-12 and IL-23 delivered by DC during vaccination. p40−/− mice were immunized with WT, p35−/−, or p40−/− DC. Forty days post vaccination mice were challenged with a lethal dose of Lm-OVA. Survival (A) and weight loss (B) were monitored over two weeks in the challenge mice (N=5/group). Statistical analyses were performed using a Student’s t-Test with the WT DC vaccinated group serving as the positive control.

Fig. 2

DC-produced IL-12 and IL-23 augment secondary CD8+ T cell responses in the liver of challenge mice. Mice vaccinated as described were challenged with 1 LD50 of Lm-OVA forty days post immunization. CD8+ T cell responses were determined in the spleen and liver on day 3 post challenge. The number of OVA-specific CD8+ T cells in the liver (A) and spleen (B and D), and the function of these T cells isolated from the spleen (C and E) were determined via FACs analysis after surface and intracellular cytokine staining. Statistical analyses were performed using a Student’s t-Test with the WT DC vaccinated group serving as the positive control.

Fig. 3

IL-12 and IL-23-enhanced resistance to Lm which is also evident at lower challenge doses. p40−/− mice were immunized with WT, p35−/−, or p40−/− DC. Forty days post vaccination mice were challenged with 1 LD₅₀ of Lm-OVA. Lm-OVA colonization of the liver (A) and the spleen (C) were determined on day 3 post-challenge. The percentage of mice that had cleared Lm-OVA from the liver (B) and spleen (D) was determined by the following formula: (# of mice with no detectable bacteria/# of mice with detectable bacteria) x 100.

Fig. 4

Memory CD8+ T cell development is compromised in the absence of IL-12 and IL-23. Mice were vaccinated as described and forty days post-immunization CD8+ T cell responses were assessed in the spleen and liver. The number of OVA-specific CD8+ T cells in the spleen and liver (A and B), and the function of these T cells isolated from the spleen (C and D) were determined via FACs analysis after surface and intracellular cytokine staining. Statistical analyses were performed using a Student’s t-Test with the WT DC vaccinated group serving as the positive control.

Fig. 5

Primary CD8+ T cell responses are not augmented by the presence of DC-produced IL-12 and IL-23. Mice were vaccinated as described and 7 days post-immunization CD8+ T cell responses were determined in the spleen. The number of OVA-specific CD8+ T cells (C), and the function of these T cells isolated from the spleen (A and B) were determined via FACs analysis after surface and intracellular cytokine staining. Statistical analyses were performed using a Student’s t-Test with the WT DC vaccinated group serving as the positive control.