IL-2 complex treatment can protect naive mice from bacterial and viral infection

Abstract

IL-2 complexes have substantial effects on the cellular immune system, and this approach is being explored for therapeutic application in infection and cancer. However, the impact of such treatments on subsequent encounter with pathogens has not been investigated. In this study, we report that naive mice treated with a short course of IL-2 complexes show enhanced protection from newly encountered bacterial and viral infections. IL-2 complex treatment expands both the NK and CD8 memory cell pool, including a recently described population of preexisting memory-phenotype T cells responsive to previously unencountered foreign Ags. Surprisingly, prolonged IL-2 complex treatment decreased CD8 T cell function and protective immunity. These data reveal the impact of cytokine complex treatment on the primary response to infection.

Figure 1. Enhanced protection of naïve mice against LM and VV after IL-2 complex treatment

(a) Schematic of the timing of IL-2 complex treatment and infection. (b and c) Colony forming units (CFU) of LM in the spleen (b) and liver (c) 3 days after infection with 8 × 10⁴ CFU of LM-OVA. Each symbol represents an individual mouse. (d) Plaque forming units (PFU) of VV in the ovaries of mice 3 days after infection with 2 × 10⁶ PFU of VV-WR. LOD = limit of detection.

Figure 2. IL-2 complex treatment increases CD8 T cells and NK cells that exhibit increased granzyme B expression

(a) Total numbers of CD8 T cells and NK cells in lymphoid and peripheral tissues post-IL-2 complex treatment. N = 6 per group (b) Phenotype of CD8 T cells in the spleen and liver. A representative plot is shown.

Figure 3. Increased tetramer specific CD44hi cells after IL-2 complex treatment

(a) Numbers of K^b-B8R-specific or K^b-OVA-specific CD8 T cells in the spleen and lymph nodes of control or IL-2 complex treated mice. (b) Numbers of CD44^hi tetramer positive cells. (c) Numbers of CD44^lo tetramer positive cells. Numbers indicate the fold increase compared to control animals. Each symbol represents an individual mouse.

Figure 4. Both CD8 T cells and NK cells mediate protection against LM which lasts for several weeks

(a and b) Mice were depleted of CD8+ cells or NK1.1+ cells or both during the IL-2 complex treatment phase. Depletion was confirmed in the spleen and liver to be >90%. Mice were then challenged with LM-OVA. Clearance of LM in the spleen (a) and liver (b) 3 days after infection compared to the control treated group. Data are combined from three experiments. N = 10/ group (c) Time after completion of IL-2 complex treatment was varied as indicated followed by infection with LM. CFU of LM in the spleen three days after infection is displayed. Each symbol represents an individual mouse.

Figure 5. Increased central memory pool and secondary expansion after IL-2 complex treatment

(a) Mice were control treated or treated with IL-2 complex followed by infection with LM-OVA. Six weeks after infection, the number of Kb-OVA specific CD8 T cells in the spleen was determined by tetramer staining. N = 5/group (b) Surface staining for the indicated markers was performed on Kb-OVA specific memory CD8 T cells. (c) Mice were challenged with 2 × 10⁵ LM-OVA. Five days after infection the number of Kb-OVA specific CD8 T cells was enumerated by tetramer staining. N = 5/group.

Figure 6. Multiple injections of IL-2 complex negatively impacts protection and functional responses

Mice were injected with 3 or 5 doses of IL-2 complex over the course of one week. (a) The number of endogenous K^b-B8R or K^b-0VA specific CD8 T cells in the spleen and lymph node was determined on day 7. (b) On day 8 after IL-2 complex treatment mice were infected with LM-OVA. Three days after infection, the CFU in the spleen was determined. (c) On day 8 after IL-2 complex treatment, mice were infected with VV-WR. Three days after infection, the PFU in the ovary was determined. (d) On day 7, spleen and lymph nodes were harvested from the indicated groups. ~2 × 10⁶ CD8+ CD44hi cells were adoptive transferred into new B6.SJL hosts. The next day, mice were infected with attenuated LM-OVA ActA-. Eight days after infection, the number of donor and host K^b-OVA specific cells was enumerated. N = 3/group; Data is representative of two experiments. (e) Day 7 splenocytes from the indicated groups were cultured in either: IL-2 or IL-2, IL-12, and IL-18 for ~18 hours. Surface staining followed by intracellular staining for IFNγ was performed. Numbers indicate the frequency of CD8+ CD44hi cells producing IFNγ. Data is representative of two experiments.