Interleukin-10 and antigen-presenting cells actively suppress Th1 cells in BALB/c mice infected with the filarial parasite Brugia pahangi

Abstract

Infection with the third-stage larvae (L3) of the filarial nematode Brugia results in a Th2-biased immune response in mice and humans. Previously we have shown that the production of interleukin 4 (IL-4) is critical for down-regulating polyclonal Th1 responses in L3-infected mice. However, the in vitro neutralization of IL-4 did not fully recover the defective polyclonal Th1 responses, nor did it result in the production of any antigen (Ag)-specific Th1 cytokines, suggesting that perhaps infection with L3 does not result in priming of Th1 cells in vivo. In this study, we analyzed the role of IL-10 and Ag-presenting cells (APCs) in the spleen as additional factors controlling the Th2 bias in infected mice. Our data show that IL-10 and APCs also contribute to the suppression of mitogen-driven Th1 responses of spleen cells from infected mice. In addition, the neutralization of IL-10 or the replacement of the resident APC population from spleen cell cultures resulted in the production of Ag-specific Th1 cytokines. Irradiated spleen cells from either L3-infected or uninfected mice were able to restore Ag-specific Th1 responses in vitro. Therefore, it appears that Brugia-reactive Th1 cells are primed following infection with L3, but are actively suppressed in vivo by a mechanism that involves IL-10 and the resident APC population, but not IL-4. These results indicate that a complex interplay of cytokines and cell populations underscores the Th2-polarized response in L3-infected mice.

FIG. 1

Effect of neutralizing anti-IL-10 MAb on ConA-driven responses of spleen cells from mice infected with L3. Mice were injected s.c. with 50 L3 or HBSS, and spleens were removed at day 12 p.i. ConA-stimulated cultures were incubated alone (□) or with 10 μg of either an isotype-matched control (R59-40) (▨) or anti-IL-10 (JES5-2A5) () per ml. After 48 h of incubation, proliferation (A) and IL-2 (B) and IFN-γ (C) production were measured. (A) The means of triplicate wells are expressed as SIs (cpm with ConA/cpm with medium alone). The SIs represent the means ± standard deviations of five animals per group, ∗, significant difference (P < 0.05) between the values obtained with JES5-2A5 and R59-40. SIs were also significantly different (P < 0.05) between the cells of L3-infected mice treated with JES5-2A5 and uninfected mice with no treatment. (B) and (C) Cytokine assays were performed with spleen cells pooled from five animals in each group. The results presented were comparable in two additional experiments.

FIG. 2

Effect of neutralizing anti-IL-10 MAb on Ag-driven responses of spleen cells from mice infected with L3. Mice were injected as described in the legend to Fig. 1. Ag-stimulated cultures were incubated with 10 μg of either an isotype-matched control (R59-40) (▨) or anti-IL-10 (JES5-2A5) () per ml, and proliferation (A) and IL-2 (B) and IFN-γ (C) production were measured, as described previously. (A) The SIs shown are the means ± standard deviations of five animals per group. (B and C) Cytokine assays were performed with spleen cells pooled from five animals in each group. The results presented were comparable in two additional experiments.

FIG. 3

Proliferative responses of spleen cells from BALB/c mice following s.c. or i.p. injection with L3 to ConA and B. pahangi adult Ag. Mice were injected s.c. or i.p. with 50 L3. Uninfected controls were injected s.c. with HBSS. At day 12 p.i., proliferation of spleen cells from the three groups of mice to ConA (A) or B. pahangi adult Ag (B) was measured. The SIs represent the means ± standard deviations of five animals per group. ∗, significant difference (P < 0.05) compared to uninfected controls.

FIG. 4

Effect of depletion of nylon wool-adherent cells from spleens of L3-infected mice on mitogen-driven responses. Mice were injected as described in the legend to Fig. 1. Spleen cells from five mice in each group were pooled. Splenic T cells from L3-infected mice, purified by passing the pooled spleen cell suspension over nylon wool columns, were incubated with irradiated syngeneic spleen cells from uninfected mice (▨) or with irradiated spleen cells from L3-infected mice (▩). ConA-stimulated proliferation (A) and cytokine production (B to F) were measured in these cultures and in cultures of unseparated spleen cells from L3-infected () and uninfected () mice.

FIG. 5

Effect of depletion of nylon wool-adherent cells from spleens of L3-infected mice on Ag-driven responses. Mice were injected as described in the legend to Fig. 1. Splenic T cells from L3-infected mice, purified by passing the pooled spleen cell suspension over nylon wool columns, were incubated with irradiated syngeneic spleen cells from uninfected mice (▨) or with irradiated spleen cells from L3-infected mice (▩). Ag-stimulated proliferation (A) and cytokine production (B to F) were measured in these cultures and in cultures of unseparated spleen cells from L3-infected () and uninfected () mice.