Tomomitsu Doi

Regulatory T Cells Suppress Development of Colitis, Blocking Differentiation of T-Helper 17 Into Alternative T-Helper 1 Cells

BACKGROUND & AIMS Although T-helper (Th) 17 and Th1 cells are involved in pathogenesis of intestinal inflammation, their developmental pathways and sufficiency to promote disease are not known; nor are the roles of CD4⁺CD25⁺ regulatory T (T(R)) cells in their development. METHODS We performed adoptive transfer experiments to investigate the induction and suppression of colitis using naïve CD4⁺CD45RB(high) T cells and/or CD4⁺CD25⁺ T(R) cells that were obtained from retinoid-related orphan receptor gamma t (RORγt) gfp/⁺ or Ly5.1/Ly5.2 congenic mice. RESULTS We observed 3 types of colitogenic CD4⁺ Th1 cells (interleukin [IL]-17A⁻interferon [IFN]-γ⁺): RORγt⁻ classical Th1 cells that differentiated directly from naïve T cells; RORγt⁺ Th1-like cells; and RORγt⁻ alternative Th1 cells that were terminally differentiated from RORγt⁺ cells via Th17 (IL-17A⁺IFN-γ⁻), Th17/Th1 (IL-17A⁺IFN-γ⁺), or Th1-like (IL-17A⁻IFN-γ⁺) cells. In this pathway, CD4⁺CD25⁺ T(R) cells suppress the development of not only classical Th1 cells, but also alternative Th1 cells at the transition of Th17/Th1 into alternative Th1 cells, resulting in accumulation of Th17 and Th17/Th1 cells in mice in which the development of colitis was suppressed. Furthermore, T(R) cells regulated the established balance of Th17 and Th1 cells under colitic conditions to yield a high ratio of Th17 and Th17/Th1 cells to Th1 cells in noncolitic conditions. CONCLUSIONS Th17 and Th17/Th1 cells become colitogenic alternative Th1 cells via Th17, Th17/Th1, and Th1-like cells, independently of classical Th1 cells. T(R) cells suppress this pathway, resulting in accumulation of Th17 and Th17/Th1 cells.

PI3K is a negative regulator of IgE production

The production of IgE, a main player in allergic disorders such as asthma and atopic dermatitis, is strictly regulated and the serum concentrations of IgE are normally kept at a much lower level than other isotypes. We found that mice deficient for the p85alpha regulatory subunit of class IA phosphoinositide 3-kinase (PI3K) produced increasing amounts of serum IgE. Purified p85alpha-/- B cells produced more IgE than wild-type B cells in vitro in response to anti-CD40 mAb and IL-4. PI3K inhibitors wortmannin and IC87114 enhanced IgE production by wild-type B cells stimulated with anti-CD40 mAb and IL-4. Under the same condition, antigen receptor cross-linking induced the expression of inhibitor of differentiation-2 and suppressed the expression of activation-induced cytidine deaminase and class switch recombination (CSR) in a PI3K-dependent manner. IgE production was also suppressed in a concentrated cell culture condition, which was completely reversed by PI3K inhibition. The selective suppression of IgE production by PI3K was also observed at a protein level after CSR. Our results indicate that PI3K negatively regulates IgE production at both CSR and protein levels.

The p85α Regulatory Subunit of Class IA Phosphoinositide 3-Kinase Regulates β-Selection in Thymocyte Development

We examined the role of class IA PI3K in pre-TCR controlled β-selection and TCR-controlled positive/negative selection in thymic development. Using mice deficient for p85α, a major regulatory subunit of the class IA PI3K family, the role of class IA PI3K in β-selection was examined by injection of anti-CD3ε mAb into p85α−/−Rag-2−/− mice, which mimics pre-TCR signals. Transition of CD4−CD8− double-negative (DN) to CD4+CD8+ double-positive (DP) thymocytes triggered by anti-CD3ε mAb was significantly impaired in p85α−/−Rag-2−/− compared with p85α+/−Rag-2−/− mice. Furthermore, DP cell numbers were lower in p85α−/−DO11.10/Rag-2−/− TCR-transgenic mice than in DO11.10/Rag-2−/− mice. In addition, inhibition by IC87114 of the major class IA PI3K catalytic subunit expressed in lymphocytes, p110δ, blocked transition of DN to DP cells in embryonic day 14.5 fetal thymic organ culture without affecting cell viability. In the absence of phosphatase and tensin homolog deleted on chromosome 10, where class IA PI3K signals would be amplified, the DN to DP transition was accelerated. In contrast, neither positive nor negative selection in Rag-2−/−TCR-transgenic mice was perturbed by the lack of p85α. These findings establish an important function of class IA PI3K in the pre-TCR-controlled developmental transition of DN to DP thymocytes.

IgA plasma cells express the negative regulatory co-stimulatory molecule programmed cell death 1 ligand and have a potential tolerogenic role in the intestine

To maintain immune homeostasis in the intestine, the intestinal immune system has evolved several tolerogenic mechanisms toward intestinal microflora and food antigens. Although programmed cell death-1 (PD-1) protein has been implicated in immunological tolerance in the intestine and gut-associated lymphoid tissues (GALTs), distribution of its ligands PD-L1 and PD-L2 in the small intestine lamina propria (LP) are unknown. We investigated PD-L1 expression in intestinal LP and found that IgA plasma cells (PCs) were major PD-L1 expressing cells. PD-L1 expression levels on IgA PCs were higher than that on IgG PCs in peripheral lymphoid tissues. IgA PCs expressed antigen-presenting molecule MHC class II and co-stimulatory molecules CD80, CD86, and PD-L2. IgA PCs isolated from intestinal LP exhibited antigen presentation activity, and in the presence of TGF-β induced FoxP3(+) regulatory T cells, but not IFN-γ(+) Th1 cells, from naïve T cells. Thus, IgA PCs in the intestine may be involved in an immune regulatory role in the intestinal immune system.

CCR9+ macrophages are required for eradication of peritoneal bacterial infections and prevention of polymicrobial sepsis

Sepsis is a systemic inflammatory response to infection associated with multiple organ dysfunction syndrome and a high mortality rate. In septic shock induced by severe peritonitis, early response of peritoneal macrophages against infected microbes is vital in preventing the spread of infection. We found that the mucosal homing receptor CCR9, is induced in peritoneal macrophages in response to inflammatory stimulation. We used a cecal ligation and puncture (CLP) model of sepsis to determine the role of CCR9 with respect to peritoneal macrophages, and controlling peritoneal infection and systemic inflammation. CCR9(-/-) mice showed aggravated septic shock with higher mortality rates compared with wild-type (WT) mice. Six hours after CLP, CCR9(-/-) mice demonstrated a greater inflammatory response. This was associated with higher production of inflammatory cytokines, such as IL-6, TNF and IP-10 in peritoneal lavage compared with WT mice. Although the numbers of peritoneal bacteria were elevated in CCR9(-/-) mice subjected to CLP compared with WT mice, this was normalized in CCR9(-/-) mice subjected to CLP through the adoptive transfer of WT peritoneal macrophages. We conclude that CCR9 is required for recruitment of peritoneal macrophages in the steady state to control systemic sepsis during early phases of peritoneal infection.

Soluble PD-L1 with PD-1-binding capacity exists in the plasma of patients with non-small cell lung cancer.

PD-L1 is one of the important immune checkpoint molecules that can be targeted by cancer immunotherapies. PD-L1 has a soluble form (sPD-L1) and a membrane-bound form (mPD-L1). Conventional enzyme-linked immunosorbent assay (ELISA) systems can detect sPD-L1 using anti-PD-L1 capture antibody through the antigen-antibody reaction, but cannot evaluate the quality and function of sPD-L1. In this study, we developed a novel ELISA system for the detection and quantification of sPD-L1 with PD-1-binding capacity (bsPD-L1). To capture bsPD-L1 through the ligand-receptor reaction, the anti-PD-L1 capture antibody in the conventional ELISA was replaced with PD-1-Ig fusion protein in the new ELISA. The new ELISA could detect bsPD-L1 in 29 out of 75 plasma samples from patients with non-small cell lung cancer (NSCLC), with higher sensitivity and frequency than the conventional ELISA. The western blot analysis showed that sPD-L1 in the plasma was glycosylated. Treatment of the samples with glycosidase reduced the absorbance determined by the new ELISA but had no effect on the absorbance determined by the conventional ELISA. These results suggest that glycosylation of sPD-L1 is important for its binding to the immobilized PD-1 in the new ELISA. Our new ELISA system may be useful for the evaluation of functional sPD-L1 with PD-1-binding capacity in cancer patients.