Hiromasa Hamada

Identification of Multiple Isolated Lymphoid Follicles on the Antimesenteric Wall of the Mouse Small Intestine

We have revealed that 100–200 clusters, filled with closely packed lymphocytes, can be found throughout the length of the antimesenteric wall of the mouse small intestine. They are composed of a large B cell area, including a germinal center, and epithelia overlying the clusters contain M cells. A large fraction of B cells displays B220+CD19+CD23+IgMlowIgDhighCD5−Mac-1− phenotype, and the composition of IgA+ B cells is smaller but substantial. To our knowledge, these clusters are the first identification of isolated lymphoid follicles (ILF) in mouse small intestine. ILF can be first detected at 7 (BALB/c mice) and 25 (C57BL/6 mice) days after birth, and lymphoid clusters equivalent in terms of cellular mass to ILF are present in germfree, athymic nude, RAG-2−/−, TCR-β−/−, and Ig μ-chain mutant (μm−/−) mice, although c-kit+ cells outnumber B220+ cells in germfree and athymic nude mice, and most lymphoid residents are c-kit+B220− in RAG-2−/−, TCR-β−/−, and μm−/− mice. ILF develop normally in the progeny of transplacentally manipulated Peyer’s patch (PP)-deficient mice, and decreased numbers of conspicuously atrophied ILF are present in IL-7Rα−/− PPnull mice. Neither ILF nor PP are detectable in lymphotoxin α−/− and aly/aly mice that retain well-developed cryptopatches (CP) and thymus-independent subsets of intraepithelial T cells, whereas ILF, PP, CP, and thymus-independent subsets of intraepithelial T cells disappear from common cytokine receptor γ-chain mutant mice. These findings indicate that ILF, PP, and CP constitute three distinct organized gut-associated lymphoid tissues that reside in the lamina propria of the mouse small intestine.

Tc17, a Unique Subset of CD8 T Cells That Can Protect against Lethal Influenza Challenge

We show here that IL-17-secreting CD4 T (Th)17 and CD8 T (Tc)17 effector cells are found in the lung following primary challenge with influenza A and that blocking Ab to IL-17 increases weight loss and reduces survival. Tc17 effectors can be generated in vitro using naive CD8 T cells from OT-I TCR-transgenic mice. T cell numbers expand 20-fold and a majority secretes IL-17, but little IFN-γ. Many of the IL-17-secreting cells also secrete TNF and some secrete IL-2. Tc17 are negative for granzyme B, perforin message, and cytolytic activity, in contrast to Tc1 effectors. Tc17 populations express message for orphan nuclear receptor γt and FoxP3, but are negative for T-bet and GATA-3 transcription factors. The FoxP3-positive, IL-17-secreting and IFN-γ-secreting cells represent three separate populations. The IFN-γ-, granzyme B-, FoxP3-positive cells and cells positive for IL-22 come mainly from memory cells and decrease in number when generated from CD44low rather than unselected CD8 T cells. Cells of this unique subset of CD8 effector T cells expand greatly after transfer to naive recipients following challenge and can protect them against lethal influenza infection. Tc17 protection is accompanied by greater neutrophil influx into the lung than in Tc1-injected mice, and the protection afforded by Tc17 effectors is less perforin but more IFN-γ dependent, implying that different mechanisms are involved.

Peyer's patch is the essential site in initiating murine acute and lethal graft-versus-host reaction.

Acute graft-versus-host disease (a-GVHD) is initiated primarily by immunologically competent cytotoxic T cells (CTLs) that express anti-host specificities. However, the host lymphoid compartment in which these precursor CTLs are initially stimulated remains unclear. Here we show that gut Peyers patches (PPs) are required to activate anti-host CTL responses in a well characterized murine acute graft-versus-host reaction (a-GVHR) model, involving transfer of parent lymphocytes into F1 hybrid recipients. The a-GVHR was prevented when recruitment of donor T cells into PP was interrupted either by disrupting the gene encoding chemokine receptor CCR5 or by blocking integrin α4β7–MAdCAM-1 (mucosal vascular addressin) interactions. Mice deficient for PPs failed to develop a-GVHD in two models of disease induction. Thus, blockade of CTL generation in PPs might offer new strategies for circumventing a-GVHD.

IL-10 Deficiency Unleashes an Influenza-Specific Th17 Response and Enhances Survival against High-Dose Challenge

We examined the expression and influence of IL-10 during influenza infection. We found that IL-10 does not impact sublethal infection, heterosubtypic immunity, or the maintenance of long-lived influenza Ag depots. However, IL-10-deficient mice display dramatically increased survival compared with wild-type mice when challenged with lethal doses of virus, correlating with increased expression of several Th17-associated cytokines in the lungs of IL-10-deficient mice during the peak of infection, but not with unchecked inflammation or with increased cellular responses. Foxp3− CD4 T cell effectors at the site of infection represent the most abundant source of IL-10 in wild-type mice during high-dose influenza infection, and the majority of these cells coproduce IFN-γ. Finally, compared with predominant Th1 responses in wild-type mice, virus-specific T cell responses in the absence of IL-10 display a strong Th17 component in addition to a strong Th1 response and we show that Th17-polarized CD4 T cell effectors can protect naive mice against an otherwise lethal influenza challenge and utilize unique mechanisms to do so. Our results show that IL-10 expression inhibits development of Th17 responses during influenza infection and that this is correlated with compromised protection during high-dose primary, but not secondary, challenge.

Gut Cryptopatches: Direct Evidence of Extrathymic Anatomical Sites for Intestinal T Lymphopoiesis

Athymic cytokine receptor gamma chain mutant mice that lack the thymus, Peyers patches, cryptopatches (CP), and intestinal T cells were reconstituted with wild-type bone marrow cells. Bone marrow-derived TCR(-) intraepithelial lymphocytes (IEL) first appeared within villous epithelia of small intestine overlying the regenerated CP, and these TCR(-) IEL subsequently emerged throughout the epithelia. Thereafter, TCR(+) IEL increased to a comparable number to that in athymic mice and consisted of TCRgammadelta and TCRalphabeta IEL. In gut-associated lymphoid tissues of wild-type mice, only CP harbored a large population of c-kit(high)IL-7R(+)CD44(+)Thy-1(+/-)CD4(+/-)CD25(low/-)alpha(E) beta(7)(-)Lin(-) (Lin, lineage markers) lymphocytes that included cells expressing germline but not rearranged TCRgamma and TCRbeta gene transcripts. These findings provide direct evidence that gut CP develop progenitor T cells for extrathymic IEL descendants.

Role of γδT Cells in the Inflammatory Response of Experimental Colitis Mice

We examined the severity of experimental colitis induced by dextran sulfate sodium (DSS) using immunologically manipulated mice. C57BL/6 mice showed more severe colitis than BALB/c mice, but mice of both strains recovered fully from the disease after the removal of DSS from their drinking water. The infiltrated cells at the lesions were mainly granulocytes in normal littermates. However, C.B-17 scid, IL-7Rα deficient, and TCR-Cβδ double-deficient mice showed severe colitis and did not recover from the disease even after the removal of DSS. It was found that the infiltrated cells at the lesions in the lethal strains were monocytes. Although both TCR-Cδ−/− and TCR-Cβ−/− mice showed severe colitis phenotypes, infiltration in the former is monocyte-dominant while that in the latter is granulocyte-dominant. Thus the type of cells that infiltrate at the lesions of DSS-induced experimental colitis may be controlled by functional T cell subsets. Immunohistological and RT-PCR analyses of the inflamed colon revealed that the murine homologue of human GROα released by some cells under the control of γδT cells is a possible candidate determining the severity of DSS-induced experimental colitis.

Adoptive Transfer of Tumor-Specific Tc17 Effector T Cells Controls the Growth of B16 Melanoma in Mice

In vitro generated OVA-specific IL-17–producing CD8 T effector cells (Tc17) from OT-1 mice, adoptively transferred into B16-OVA tumor-bearing mice, controlled tumor growth in early and late stage melanoma. IL-17, TNF, and IFN-γ from the Tc17 effectors all played a role in an enhanced recruitment of T cells, neutrophils, and macrophages to the tumor. In addition, Tc17 cells and recently recruited, activated neutrophils produced further chemokines, including CCL3, CCL4, CCL5, CXCL9, and CXCL10, responsible for the attraction of type 1 lymphocytes (Th1 and Tc1) and additional neutrophils. Neutrophils were rapidly attracted to the tumor site by an IL-17 dependent mechanism, but at later stages the induction of the chemokine CXCL2 by Tc17-derived TNF and IFN-γ contributed to sustain neutrophil recruitment. Approximately 10–50 times as many Tc17 effectors were required compared with Tc1 effectors to exert the same level of control over tumor growth. The recruitment of neutrophils was more prominent when Tc17 rather than Tc1 were used to control tumor and depletion of neutrophils resulted in a diminished capacity to control tumor growth.

Multiple Redundant Effector Mechanisms of CD8+ T Cells Protect against Influenza Infection

We have previously shown that mice challenged with a lethal dose of A/Puerto Rico/8/34-OVAI are protected by injection of 4–8 × 106 in vitro–generated Tc1 or Tc17 CD8+ effectors. Viral load, lung damage, and loss of lung function are all reduced after transfer. Weight loss is reduced and survival increased. We sought in this study to define the mechanism of this protection. CD8+ effectors exhibit multiple effector activities, perforin-, Fas ligand–, and TRAIL-mediated cytotoxicity, and secretion of multiple cytokines (IL-2, IL-4, IL-5, IL-9, IL-10, IL-17, IL-21, IL-22, IFN-γ, and TNF) and chemokines (CCL3, CCL4, CCL5, CXCL9, and CXCL10). Transfer of CD8+ effectors into recipients, before infection, elicits enhanced recruitment of host neutrophils, NK cells, macrophages, and B cells. All of these events have the potential to protect against viral infections. Removal of any one, however, of these potential mechanisms was without effect on protection. Even the simultaneous removal of host T cells, host B cells, and host neutrophils combined with the elimination of perforin-mediated lytic mechanisms in the donor cells failed to reduce their ability to protect. We conclude that CD8+ effector T cells can protect against the lethal effects of viral infection by means of a large number of redundant mechanisms.

Tc17 Cells Are Capable of Mediating Immunity to Vaccinia Virus by Acquisition of a Cytotoxic Phenotype

CD8 T cells can acquire cytokine-secreting phenotypes paralleling cytokine production from Th cells. IL-17–secreting CD8 T cells, termed Tc17 cells, were shown to promote inflammation and mediate immunity to influenza. However, most reports observed a lack of cytotoxic activity by Tc17 cells. In this study, we explored the anti-viral activity of Tc17 cells using a vaccinia virus (VV) infection model. Tc17 cells expanded during VV infection, and TCR transgenic Tc17 cells were capable of clearing recombinant VV infection. In vivo, adoptively transferred Tc17 cells lost the IL-17–secreting phenotype, even in the absence of stimulation, but they did not acquire IFN-γ–secreting potential unless stimulated with a virus-encoded Ag. However, examination of cells following infection demonstrated that these cells acquired cytotoxic potential in vivo, even in the absence of IFN-γ. Cytotoxic potential correlated with Fasl expression, and the cytotoxic activity of postinfection Tc17 cells was partially blocked by the addition of anti-FasL. Thus, Tc17 cells mediate VV clearance through expression of specific molecules associated with cytotoxicity but independent of an acquired Tc1 phenotype.

Abundance of unconventional CD8(+) natural killer T cells in the large intestine.

Natural killer T (NKT) cells are mainly present in the liver and thymus, and the majority of these T cells express either a CD4+ or a double‐negative (DN) CD4–8– phenotype. In the present study, we examined whether such NKT cells were present in the intestine. NKT cells were rare in all sites of the small intestine, including an intraepithelial site. However, aconsiderable number of NKT cells were found at an intraepithelial site in the large intestine. This result was confirmed by both immunofluorescence and immunohistochemistry. In contrast to conventional NKT cells, NKT cells in the large intestine were CD8+ or DN CD4–8–. In the case of conventional NKT cells, their existence is known to depend on non‐classical MHC class I‐like antigens (i. e. CD1d) but not on classical MHC class I antigens. However, the NKT cells in the large intestine were independent of the presence of both CD1d and classical MHC class I antigens. These results were obtained using knockout mice lacking the corresponding genes and molecules. NKT cells in the large intestine were mainly α βTCR+ (> 75 %) but did not use an invariant chain of Vα14Jα281, which is preferentially used by conventional NKT cells. These NKT cells did not bias the TCR‐Vβ usage toward Vβ8. These findings suggest that the large intestine is a site in which unconventional NKT cells carrying the CD8+ phenotype (or DN CD4–8–) are abundant and that these cells are independent of MHC andMHC‐like antigens.