Regulatory T cell-like responses in deer mice persistently infected with Sin Nombre virus

Abstract

Hantavirus cardiopulmonary syndrome is a zoonotic illness associated with a systemic inflammatory immune response, capillary leak, noncardiogenic pulmonary edema, and shock in humans. Cytokines, including TNF, IFN-gamma, and lymphotoxin, are thought to contribute to its pathogenesis. In contrast, infected rodent reservoirs of hantaviruses experience few or no pathologic changes and the host rodent can remain persistently infected for life. Generally, it is unknown why such dichotomous immune responses occur between humans and reservoir hosts. Thus, we examined CD4(+) T cell responses from one such reservoir, the deer mouse (Peromyscus maniculatus), infected with Sin Nombre virus. Proliferation responses to viral nucleocapsid antigen were relatively weak in T cells isolated from deer mice, regardless of acute or persistent infection. The T cells from acutely infected deer mice synthesized a broad spectrum of cytokines, including IFN-gamma, IL-4, IL-5, and TGF-beta(1), but not TNF, lymphotoxin, or IL-17. However, in T cells from persistently infected deer mice, only TGF-beta(1) was expressed by all lines, whereas some expressed reduced levels of IFN-gamma or IL-5. The Forkhead box P3 transcription factor, a marker of some regulatory T cells, was expressed by most of these cells. Collectively, these data suggest that TGF-beta(1)-expressing regulatory T cells may play an important role in limiting immunopathology in the natural reservoir host, but this response may interfere with viral clearance. Such a response may have arisen as a mutually beneficial coadaptive evolutionary event between hantaviruses and their rodent reservoirs, so as to limit disease while also allowing the virus to persist.

Fig. 1.

T cells from SNV-infected deer mice are not persistently infected. T cell lines were established from three deer mice (DM5516, DM5600, and DM5603) and sampled at days 10 and 25 of culture. TaqMan real-time PCR was used to quantify copies of viral S segment. By day 25, viral RNA could not be detected (ND).

Fig. 2.

Molecular phenotypes of cultured T cells from infected deer mice. RNA from cultured T cells was reverse transcribed for PCR to detect the expression of CD4, T-bet, GATA3, and FoxP3. All cells were CD4⁺ and T-bet⁺, whereas only T cells from acutely infected deer mice expressed GATA3. FoxP3 expression was detected in some of the acutely and persistently infected deer mice.

Fig. 3.

T cells from SNV-infected deer mice exhibit weak recall proliferation responses to N-Ag. T cell lines established from acutely infected deer mice (A) and persistently infected deer mice (B) were cultured in duplicate with autologous bone-marrow-derived APCs at various concentrations of antigen for 3 days; after which, proliferation was assessed by MTS assay. The means and SDs were plotted and compared with T cells from control deer mice immunized with KLH (DM21 and DM22).

Fig. 4.

Cytokine responses of T cell lines from acutely and persistently infected deer mice. (A) T cells from acutely infected deer mice expressed IFN-γ, IL-4, IL-5, TGF-β₁, and IL-10 but not TNF or LT. (B) Lines from persistently infected deer mice expressed TGF-β₁ but not TNF, LT, IL-4, or IL-10. DM6001 also expressed IFN-γ and deer mice DM6010 and DM6019 also expressed IFN-γ and IL-5. Expression levels denoted by * are significantly different (P < 0.05) from the same cytokine expressed by T cells from acutely infected deer mice. RTA, relative template abundance.