Richard W. Dutton

Activated Antigen-Specific CD8 + T Cells Persist in the Lungs Following Recovery from Respiratory Virus Infections

The poor correlation between cellular immunity to respiratory virus infections and the numbers of memory CD8+ T cells in the secondary lymphoid organs suggests that there may be additional reservoirs of T cell memory to this class of infection. Here we identify a substantial population of Ag-specific T cells in the lung that persist for several months after recovery from an influenza or Sendai virus infection. These cells are present in high numbers in both the airways and lung parenchyma and can be distinguished from memory cell populations in the spleen and peripheral lymph nodes in terms of the relative frequencies among CD8+ T cells, activation status, and kinetics of persistence. In addition, these cells are functional in terms of their ability to proliferate, express cytolytic activity, and secrete cytokines, although they do not express constitutive cytolytic activity. Adoptive transfer experiments demonstrated that the long-term establishment of activated T cells in the lung did not require infection in the lung by a pathogen carrying the inducing Ag. The kinetics of persistence of Ag-specific CD8+ T cells in the lung suggests that they play a key role in protective cellular immunity to respiratory virus infections.

Type 1 and Type 2: a fundamental dichotomy for all T-cell subsets

Cytokine secretion is not confined to CD4+ T cells; rather, Type 1 and Type 2 populations of CD8+ and gamma delta T cells can also be generated in vitro and isolated from in vivo situations. These subsets and their physiological functions are significant.

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.

Is There Evidence for a Non-Antigen Specific Diffusable Chemical Mediator from the Thymus-Derived Cell in the Initiation of the Immune Response?*

Publisher Summary This chapter discusses evidence for a nonantigen specific diffusable chemical mediator from the thymus-derived cell in the initiation of the immune response. The chapter focuses on mechanisms of B-cell–T-cell interaction. It presents a model in which the B cell is only triggered when it receives two signals, one from the interaction of its immunoglobulin receptor with antigen and the second from a stimulated T cell. The latter signal is itself triggered by interaction of the cells immunoglobulin receptor with antigen. The signal itself is a diffusible chemical mediator and is not antigen specific. It can signal any B cell within reach. The only limitation is the effective distance of the diffusion gradient of the chemical mediator. In this model, there is no mandatory requirement for linked recognition. The chapter highlights that this model is very close to the later model of Bretscher and Cohn. It differs in that it provides no statement as to the mechanism of tolerance induction and in that it does specify the nature of the second signal.

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.

Immunization of Normal Mouse Spleen Cell Suspensions in vitro

Dissociated cells from the spleens of unimmunized mice were cultured with and without various mammalian erythrocytes. Spleen cell suspensions cultured with heterologous red cells developed levels of hemolytic plaque-forming cells only one log2 less than those seen in vivo. The reaction is specific for the in vitro immunizing erythrocytes. Antibody was demonstrated in the culture fluids.

Immune Response Restoration with Macrophage Culture Supernatants

Depression of the in vitro immune response of mouse spleen cell suspensions to sheep erythrocytes by removal of macrophages can be reversed by the addition of supernatants from peritoneal macrophage cultures. Supernatant activity can be absorbed by the red cell antigen, and supernatant-treated red cells are stimulatory in the absence of macrophages or supernatant.

Heterogeneity of CD4(+) and CD8(+) T cells.

There is extensive plasticity in the T-cell response to antigen. Helper CD4(+) T cells, cytotoxic CD8(+) T cells, the progression from naïve to effector and memory T cells, and differentiation into Th1, Tc1, Th2 and Tc2 subsets have long been recognized. More recently it has become apparent that T-cell populations display additional diversity in terms of phenotype, anatomical distribution and effector function.

Memory CD4+ T cells induce innate responses independently of pathogen

Inflammation induced by recognition of pathogen-associated molecular patterns markedly affects subsequent adaptive responses. We asked whether the adaptive immune system can also affect the character and magnitude of innate inflammatory responses. We found that the response of memory, but not naive, CD4+ T cells enhances production of multiple innate inflammatory cytokines and chemokines (IICs) in the lung and that, during influenza infection, this leads to early control of virus. Memory CD4+ T cell–induced IICs and viral control require cognate antigen recognition and are optimal when memory cells are either T helper type 1 (TH1) or TH17 polarized but are independent of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) production and do not require activation of conserved pathogen recognition pathways. This represents a previously undescribed mechanism by which memory CD4+ T cells induce an early innate response that enhances immune protection against pathogens.

Priming with Cold-Adapted Influenza A Does Not Prevent Infection but Elicits Long-Lived Protection against Supralethal Challenge with Heterosubtypic Virus

We show in this study several novel features of T cell-based heterosubtypic immunity against the influenza A virus in mice. First, T cell-mediated heterosubtypic protection against lethal challenge can be generated by a very low priming dose. Second, it becomes effective within 5–6 days. Third, it provides protection against a very high dose challenge for >70 days. Also novel is the finding that strong, long-lasting, heterosubtypic protection can be elicited by priming with attenuated cold-adapted strains. We demonstrate that priming does not prevent infection of the lungs following challenge, but leads to earlier clearance of the virus and 100% survival after otherwise lethal challenge. Protection is dependent on CD8 T cells, and we show that CD4 and CD8 T cells reactive to conserved epitopes of the core proteins of the challenge virus are present after priming. Our results suggest that intranasal vaccination with cold-adapted, attenuated live virus has the potential to provide effective emergency protection against emerging influenza strains for several months.