Retrovirus-specificity of regulatory T cells is neither present nor required in preventing retrovirus-induced bone marrow immune pathology

Abstract

Chronic viral infections of the hematopoietic system are associated with bone marrow dysfunction, to which both virus-mediated and immune-mediated effects may contribute. Using unresolving noncytopathic Friend virus (FV) infection in mice, we showed that unregulated CD4(+) T cell response to FV caused IFN-gamma-mediated bone marrow pathology and anemia. Importantly, bone marrow pathology was triggered by relative insufficiency in regulatory T (Treg) cells and was prevented by added Treg cells, which suppressed the local IFN-gamma production by FV-specific CD4(+) T cells. We further showed that the T cell receptor (TCR) repertoire of transgenic Treg cells expressing the beta chain of an FV-specific TCR was virtually devoid of FV-specific clones. Moreover, anemia induction by virus-specific CD4(+) T cells was efficiently suppressed by virus-nonspecific Treg cells. Thus, sufficient numbers of polyclonal Treg cells may provide substantial protection against bone marrow pathology in chronic viral infections.

Figure 1

T Cell Reactivity to env_122–141 and TCR Vα2 Usage in EF4.1 TCRβ-Transgenic Mice (A) Flow-cytometric example of CD69 and CD40L induction in CD4⁺ EF4.1 TCRβ-transgenic T cells 18 hr after stimulation with the env_122–141 peptide. (B) Mean (±SEM) percentage of responding cells in total CD4⁺ T cells from EF4.1 TCRβ-transgenic or wild-type control mice 18 hr after stimulation. (C) Mean (±SEM) percentage of responding cells in gated TCR Vα2⁺ or Vα2⁻ CD4⁺ T cells from EF4.1 TCRβ-transgenic 18 hr after stimulation. (D) Mean (±SEM) percentage of responding cells, plotted as a fraction of the maximal response, in gated TCR Vα2⁺ or Vα2⁻ CD4⁺ T cells from EF4.1 TCRβ-transgenic 18 hr after stimulation. (E) TCR Vα2⁺ T cells in responding (CFSE⁻) or nonresponding (CFSE⁺) CD4⁺ T cells from EF4.1 TCRβ-transgenic 3 days after stimulation. Values in (A)–(E) are representative of five independent experiments.

Figure 2

Continuous T Helper Cell Response to Unresolving FV Infection Causes Bone Marrow Pathology (A) Changes in RBC counts in Rag1^−/− mice, which were infected with FV (FV only) or received EF4.1 TCRβ-transgenic CD4⁺ T cells (T cells only), or both (T cells + FV). Values represent the mean (±SEM) of 8–18 mice per group per time point, analyzed in more than three independent experiments. p < 0.001 between “T cells + FV” group and all other groups for days 14–35. (B–D) Total bone marrow cellularity (B) and numbers of Ter119⁺ erythroid precursor cells (C) and CD11b⁺Gr1⁺ bone marrow cells (D) in the same recipient mice. The dashed line represents the average cell numbers of untreated Rag1^−/− mice. Values are the mean (±SEM) of 5–13 mice per group on day 21. Numbers within the graphs denote the p values. (E–G) Percentages of uninfected and FV-infected (glyco-Gag⁺) Ter119⁺ and CD11b⁺Gr1⁺ cells in the bone marrow of the same groups of mice described in (A). Numbers within the plots represent the percentage of positive cells are the average of more than five mice per group analyzed on day 21. (H–K) Percentage (H and J) and absolute numbers (I and K) of CD4⁺ T cells and percentage of TCR Vα2⁺ T cells in total CD4⁺ T cells (H and J) in the spleen (H and I) or the bone marrow (J and K) of uninfected (−FV) or FV-infected (+FV) recipients of EF4.1 TCRβ-transgenic CD4⁺ T cells. Values are representative of 5–8 mice per group analyzed on day 21.

Figure 3

Suppression of Bone Marrow Pathology by Treg Cells in a Dose-Dependent Manner (A) Absolute numbers of naive CD44^loCD25⁻, memory (mem.) CD44^hiCD25⁻ or regulatory (reg.) CD25⁺ CD4⁺ T cells in secondary lymphoid organs of EF4.1 TCRβ-transgenic (TCRβ-tg) and wild-type control mice. Values are the mean (±SEM) of six mice per group and numbers within the graphs denote the p value. (B) CD25 and FoxP3 staining in gated CD4⁺ T cells from EF4.1 TCRβ-transgenic (TCRβ-tg) and wild-type control mice. Numbers within the quadrants denote the percentages of positive cells and are representative of three mice per group. (C) Changes in RBC counts in FV-infected Rag1^−/− mice, which received total EF4.1 TCRβ-transgenic CD4⁺ T cells (Ttotal), FACS-purified Treg-depleted naive CD45RB^hiCD25⁻ CD4⁺ T cells (Tnaive), or total CD4⁺ T cells together with FACS-purified CD25⁺ CD4⁺ T cells at 1:1 ratio (Ttotal + Treg). Values represent the mean (±SEM) of 8–12 mice per group per time point analyzed in three independent experiments. p = 0.0002 between “Ttotal” and “Ttotal + Treg,” and p = 0.00002 between “Ttotal” and “Tnaive,” on day 21. (D and E) Numbers of Ter119⁺ erythroid precursor cells (D) and CD11b⁺Gr1⁺ bone marrow cells (E) in FV-infected Rag1^−/− mice, which received EF4.1 TCRβ-transgenic CD4⁺ T cells, alone or together with EF4.1 TCRβ-transgenic Treg cells at 1:1 ratio. The dashed line represents the average cell numbers of untreated, uninfected Rag1^−/− mice. Values are the mean (±SEM) of 5–8 mice per group on day 21. Numbers within the graphs denote the p values.

Figure 4

Treg-Mediated Suppression of Local IFN-γ Production by Conventional EF4.1 TCRβ-Transgenic CD4⁺ T Cells in the Bone Marrow (A–D) Percentage of IL-17A and IFN-γ producing cells in total CD45.1⁺ EF4.1 TCRβ-transgenic CD4⁺ T cells, isolated from the spleen (A and B) or the bone marrow (C and D) of FV-infected Rag1^−/− mice, which received total CD45.1⁺ EF4.1 TCRβ-transgenic CD4⁺ T cells, alone (−) or together (+ Treg) with CD45.2⁺ EF4.1 TCRβ-transgenic Treg cells at 1:1 ratio. Values are representative of six to nine mice per group, analyzed either on day 21 or day 35 with identical results. Numbers within the bar graphs and dot plots denote the p values and percentage of positive cells, respectively. The median fluorescence intensity (MFI) ± SEM of IFN-γ staining in C was “− Treg” = 160 ± 19; “+ Treg” = 105 ± 15; p = 0.0003, Student's t test, n = 6. (E) Serum IFN-γ concentration in FV-infected Rag1^−/− mice, which received total CD45.1⁺ EF4.1 TCRβ-transgenic CD4⁺ T cells, alone (−) or together (+ Treg) with CD45.2⁺ EF4.1 TCRβ-transgenic Treg cells at 1:1 ratio. Values represent the mean (±SEM) of four to five mice per group analyzed on day 35. The dashed line depicts the basal concentration of serum IFN-γ in unmanipulated Rag1^−/− mice. Numbers within the graph denote the p values. (F) Changes in RBC counts in Rag1^−/−Ifngr1^+/+ (Ifngr1^+/+) or Rag1^−/−Ifngr1^−/− (Ifngr1^−/−) mice either infected with FV alone (Ifngr1^+/+; Ifngr1^−/−) or infected with FV and received CD4⁺ T cells (Ifngr1^+/+ + T cells; Ifngr1^−/− + T cells). Values represent the mean (±SEM) of 12–15 mice per group per time point analyzed in three independent experiments. p < 0.0001 between “Ifngr1^+/+ + T cells” and “Ifngr1^−/− + T cells,” on days 14 and 21.

Figure 5

Lack of env Reactivity in EF4.1 TCRβ-Transgenic CD4⁺ Treg Cells (A–D) CFSE dilution profile of conventional EF4.1 TCRβ-transgenic CD4⁺ T cells (A and C) and IL-2 concentration in supernatants (B and D) of cultures of CD45.1⁺ naive CD45RB^hiCD25⁻ EF4.1 TCRβ-transgenic CD4⁺ T cells, with (+ Treg) or without an equal number of CD45.2⁺ CD25⁺ EF4.1 TCRβ-transgenic Treg cells, stimulated either with anti-CD3 (A and B) or with the env_122-141 peptide (C and D) presented by bone marrow-derived dendritic cells. IL-2 concentration and CFSE profiles were assayed on days 2 and 3 of culture, respectively. Specifically for env_122–141 peptide stimulation, the CFSE profile of responding cells only is shown. No differences in the fraction of responding cells were observed in the presence or absence of Treg cells. Numbers within the plots denote the mean division number of responding cells. (E and F) CFSE dilution profile of purified CD25⁻ or CD25⁺ EF4.1 TCRβ-transgenic (E) or OT-II TCRαβ-transgenic (F) CD4⁺ T cells, 5 days after stimulation by bone marrow-derived dendritic cells in the absence of specific peptides (−) or presenting either env_122–141 or ova_323–339 peptides. Numbers within the quadrants represent the percentage of divided cells. One experiment, representative of four similar experiments, is shown. (G) A^b-env tetramer staining and CD25 expression in gated CD4⁺ T cells from wild-type and EF4.1 TCRβ-transgenic mice. Numbers within the quadrants indicate the percentage of positive cells. (H) Percentage of naive, memory (mem.), and regulatory (reg.) cells in gated A^b-env⁻ or A^b-env⁺ EF4.1 TCRβ-transgenic CD4⁺ T cells. Numbers within the graph denote the p values. Data were obtained from four mice per group.

Figure 6

Suppression of env-Specific CD4⁺ T Cell-Induced Bone Marrow Pathology by env-Nonspecific Treg Cells (A and B) Percentage of CD45.2⁺ CD4⁺ Treg cells in total CD4⁺ T cells (top row) and percentage of TCR Vα2⁺ T cells in CD45.2⁺ CD4⁺ Treg cells (bottom row), in the spleen (A) or the bone marrow (B) of FV-infected Rag1^−/− recipients, after cotransfer of CD45.1⁺ EF4.1 TCRβ-transgenic total CD4⁺ T cells with either EF4.1 TCRβ-transgenic (TCRβ-tg) or wild-type CD45.2⁺ CD25⁺ CD4⁺ Treg cells, at 1:1 ratio. Numbers within the plots indicate the percentage of positive cells and are representative of six to eight mice per group, analyzed on day 21 after transfer. (C) Changes in RBC counts in FV-infected Rag1^−/− mice, which received total EF4.1 TCRβ-transgenic CD4⁺ T cells, alone (Ttotal) or together with either EF4.1 TCRβ-transgenic (Ttotal + tg Treg) or wild-type (Ttotal + wt Treg) CD25⁺ CD4⁺ Treg cells. Values represent the mean (±SEM) of six to ten mice per group per time point analyzed in three independent experiments. p < 0.0003 between “Ttotal” and either “Ttotal + tg Treg” or “Ttotal + wt Treg” on day 21. (D) A^b-env tetramer staining in CD4⁺ T cells from the spleen or the bone marrow of FV-infected Rag1^−/− recipients, after cotransfer of CD45.1⁺ EF4.1 TCRβ-transgenic total CD4⁺ T cells with CD45.2⁺ wild-type CD25⁺ CD4⁺ Treg cells, at 1:1 ratio. Numbers within the quadrants indicate the percentage of tetramer positive cells in either CD45.1⁺ or CD45.2⁺ CD4⁺ T cells and are representative of four mice per group, analyzed on day 21 after transfer. (E) Changes in RBC counts in FV-infected Rag1^−/− mice, which received either total CD4⁺ T cells (wt Ttotal) or purified naive CD45RB^hiCD25⁻ CD4⁺ T cells (wt Tnaive) from wild-type donor mice or no T cells (no cells). Values represent the mean (±SEM) of nine to ten mice per group per time point analyzed in two independent experiments. p < 0.0003 between “wt Tnaive” and “wt Ttotal,” on day 21.

Figure 7

Potential Mechanisms of Treg Cell Activation and Action in FV-Induced Bone Marrow Pathology (A) Changes in RBC counts in FV-infected Rag1^−/− mice, which received either no T cells (no cells) or total EF4.1 TCRβ-transgenic CD4⁺ T cells either alone (Ttotal) or together with wild-type (Ttotal + wt Treg) or IL-10-deficient CD25⁺ CD4⁺ Treg cells (Ttotal + Il10^−/− Treg). Values represent the mean (±SEM) of five to six mice per group per time point analyzed in a single experiment. p < 0.001 and p < 0.02 between “Ttotal” and “Ttotal + Il10^−/− Treg,” on days 14 and 21, respectively; the p value was not significant between “Ttotal + wt Treg” and “Ttotal + Il10^−/− Treg.” (B) Expression of individual endogenous TCR Vβ5.1/5.2, Vβ6, Vβ8.1/8.2, Vβ11, and Vβ14 chains in EF4.1 TCRβ-transgenic Treg cells recovered from the lymph nodes (LNs), the spleen (SP) or the bone marrow (BM) of uninfected (− FV) or FV-infected (+ FV) Rag1^−/− recipients, which received CD45.2⁺ EF4.1 TCRβ-transgenic CD25⁺ CD4⁺ Treg cells together with CD45.1⁺ EF4.1 TCRβ-transgenic total CD4⁺ T cells, at 1:1 ratio. Expression in EF4.1 TCRβ-transgenic Treg cells before (input) and 21 days after transfer (recovered) is shown. Values represent the mean (±SEM) of two to four individual recipients from a single experiment. (C) CFSE dilution profile of CD45.1⁺ CD4⁺ Treg cells in the lymph nodes (LN), spleen (SP), and bone marrow (BM) of FV-infected Rag1^−/− recipients, which received CD45.2⁺ EF4.1 TCRβ-transgenic total CD4⁺ T cells, at the time of FV infection, and a second cohort of CFSE-labeled CD45.1⁺ wild-type CD25⁺ CD4⁺ Treg cells 21 days later. Organs were analyzed 3 days after transfer of the second Treg cell cohort. Numbers within the quadrants denote the percentage of undivided cells and are representative of four mice analyzed in two separate experiments. p < 0.007 between “BM” and either “LN” or “SP.” (D and E) Absolute number of CD45.2⁺ Treg cells recovered from the spleen (D) or the bone marrow (E) of uninfected (− FV) or FV-infected (+ FV) Rag1^−/− recipients, which received CD45.2⁺ wild-type CD25⁺ CD4⁺ Treg cells alone (− Te cells) or together with CD45.1⁺ EF4.1 TCRβ-transgenic total CD4⁺ T cells at 1:1 ratio (+ Te cells). Values represent the mean (±SEM) of three to six mice per group analyzed on day 21.