Eosinophils downregulate lung alloimmunity by decreasing TCR signal transduction

Abstract

It has been demonstrated by us as well as others that eosinophils may alter their phenotype and function based on the local environment (7, 9, 10). Since costimulation plays a critical role in T cell cytokine production and environmental polarization (11, 12), we examined the possibility that eosinophils may lose their tolerogenic properties in the absence of CSB immunosuppression. Cytokine expression was examined in BALB/c (H2 d) lung allografts transplanted into fully MHC-mismatched C57BL/6 (B6) (H2 b) recipient mice. In the absence of immunosuppression, lung allografts had higher levels of Th1-polarizing cytokines IFN-γ and TNF-α than did CSB-treated accepting lung grafts (Figure 1A). Limited amounts of Th2-polarizing cytokines IL-4, IL-13, IL-33, and GM-CSF were evident in lung allografts treated with or without CSB immunosuppression (Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.128241DS1). We next evaluated lung-resident eosinophils from both CSB-treated and nonimmunosuppressed grafts. Based on a previously identified eosinophil polarization phenotype (7), we noted higher levels of Th1-defining (or E1-defining) features, such as CXCL9, CXCL10, CXCL11, and iNOS in eosinophils isolated from rejecting compared with CSB-treated lung allografts (Figure 1A). In no group was Th2 (or E2) polarization of eosinophils detected (Supplemental Figure 1A). Flow cytometric characterization demonstrated an absence of MHC II and costimulatory molecules such as CD80, CD86, and CD40. However, there were high levels of recipient-derived MHC I (H2K b), PD-L1, and CD101 on lung-resident eosinophils in the absence of CSB (Figure 1B). Notably, we did not detect BALB/c-derived H2 d-MHC on graft-resident eosinophils, indicating a lack of "cross-dressing" or antigen swapping for donor derived-antigens (ref. 13 and Supplemental Figure 1B). Thus, while eosinophils from rejecting lungs resembled those from accepting lungs in some aspects, we did observe some differences. It is thus possible that in the absence of immunosuppression, eosinophils may contribute to graft rejection rather than acceptance, specifically because CD101 expression has been previously associated with an inflammatory eosinophil subtype (14). In order to evaluate this directly, we conditionally depleted eosinophils from B6 iPHIL mice, in which the diphtheria toxin (DT) receptor is expressed under the control of the eosinophil peroxidase promoter (Supplemental Figure 1C and ref. 15). DT-treated mice or saline-injected controls were challenged with a BALB/c lung allograft in the absence of immunosuppression. Surprisingly, mice depleted of eosinophils had higher grades of rejection (Figure 1C), increased numbers of lung-resident T lymphocytes, increased rates of T cell proliferation, and increased effector cell differentiation by day 4 after engraftment (Figure 1D). These patterns of T lymphocyte activation and infiltration were especially prominent for CD8 + T cells. CD4 + T cell proliferation did ...

Deciphering the role of eosinophils in solid organ transplantation

“…Interestingly, eosinophil depletion did not ameliorate rejection but actually prevented co‐stimulatory blockade (CSB)‐mediated graft acceptance and accentuated rejection in the absence of immunosuppression (Figure ). Unlike previous reports, which demonstrated an association of Th2 cytokines with the tolerance, we demonstrated that both CSB‐treated accepting as well nonimmunosuppressed rejecting grafts demonstrate a Th1 polarized microenvironment . This was marked by increased expression of IFN‐γ and TNF‐α without significant impact on Th2‐associated cytokines such as IL‐4, GM‐CSF, and IL‐33 .…”

“…Our observation supports the unique role of pro‐inflammatory mediators in promoting lung allograft tolerance and reaffirms the uniqueness of lung‐specific immune responses . In line with Th1 polarization of the lung allograft microenvironment, eosinophils from both accepting and rejecting lung grafts were polarized to a Th1 (or E1)‐like phenotype . The Th1 signature of the lung allograft eosinophil differs from the Th2 (or E2)‐type associated with asthma and allergic inflammation …”

“…This was marked by increased expression of IFN‐γ and TNF‐α without significant impact on Th2‐associated cytokines such as IL‐4, GM‐CSF, and IL‐33 . As suspected, more pronounced Th1 polarization was evident in rejecting lungs that were not treated with immunosuppression, but even in the presence of CSB, IFN‐γ‐ and TNF‐α‐mediated responses predominated . Our observation supports the unique role of pro‐inflammatory mediators in promoting lung allograft tolerance and reaffirms the uniqueness of lung‐specific immune responses .…”

“…In order to establish clarity regarding the role of eosinophils in lung allograft homeostasis, we utilized a clinically relevant murine model of left lung transplantation . We initially depleted eosinophils from lung graft recipients through either neutralization of IL‐5 or targeted deletion in transgenic mice, where the diphtheria toxin receptor is expressed under the control of eosinophil peroxidase promoter (iPHIL mice) . Interestingly, eosinophil depletion did not ameliorate rejection but actually prevented co‐stimulatory blockade (CSB)‐mediated graft acceptance and accentuated rejection in the absence of immunosuppression (Figure ).…”

The emerging role of regulatory T cells following lung transplantation

“…logical properties of the lungs. Here, eosinophils form PD1-PDL1-dependent synapses with alloreactive T cells which results in the dissociation of the TCR-CD3 + complex 99. Some lung transplant patients receive indiscriminate T cell depletion strategies based on observations in other transplanted organs where memory T cells in particular are harmful to the allografts.…”