CD4 + CD3 - Cells Regulate the Organization of Lymphoid Tissue and T-Cell Memory for Antibody Responses

Mucosal immunology of HIV infection

Recent advances in the immunology, pathogenesis, and prevention of human immunodeficiency virus (HIV) infection continue to reveal clues to the mechanisms involved in the progressive immunodeficiency attributed to infection, but more importantly have shed light on the correlates of immunity to infection and disease progression. HIV selectively infects, eliminates, and/or dysregulates several key cells of the human immune system, thwarting multiple arms of the host immune response, and inflicting severe damage to mucosal barriers, resulting in tissue infiltration of 'symbiotic' intestinal bacteria and viruses that essentially become opportunistic infections promoting systemic immune activation. This leads to activation and recruitment or more target cells for perpetuating HIV infection, resulting in persistent, high-level viral replication in lymphoid tissues, rapid evolution of resistant strains, and continued evasion of immune responses. However, vaccine studies and studies of spontaneous controllers are finally providing correlates of immunity from protection and disease progression, including virus-specific CD4(+) T-cell responses, binding anti-bodies, innate immune responses, and generation of antibodies with potent antibody-dependent cell-mediated cytotoxicity activity. Emerging correlates of immunity indicate that prevention of HIV infection may be possible through effective vaccine strategies that protect and stimulate key regulatory cells and immune responses in susceptible hosts. Furthermore, immune therapies specifically directed toward boosting specific aspects of the immune system may eventually lead to a cure for HIV-infected patients.

Constitutive expression of TNF-related activation-induced cytokine (TRANCE)/receptor activating NF-κB ligand (RANK)-L by rat plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are a subset of DCs whose major function relies on their capacity to produce large amount of type I IFN upon stimulation via TLR 7 and 9. This function is evolutionary conserved and place pDC in critical position in the innate immune response to virus. Here we show that rat pDC constitutively express TNF-related activation-induced cytokine (TRANCE) also known as Receptor-activating NF-κB ligand (RANKL). TRANCE/RANKL is a member of the TNF superfamily which plays a central role in osteoclastogenesis through its interaction with its receptor RANK. TRANCE/RANK interaction are also involved in lymphoid organogenesis as well as T cell/DC cross talk. Unlike conventional DC, rat CD4^high pDC were shown to constitutively express TRANCE/RANKL both at the mRNA and the surface protein level. TRANCE/RANKL was also induced on the CD4^low subsets of pDC following activation by CpG. The secreted form of TRANCE/RANKL was also produced by rat pDC. Of note, levels of mRNA, surface and secreted TRANCE/RANKL expression were similar to that observed for activated T cells. TRANCE/RANKL expression was found on pDC in all lymphoid organs as well blood and BM with a maximum expression in mesenteric lymph nodes. Despite this TRANCE/RANKL expression, we were unable to demonstrate in vitro osteoclastogenesis activity for rat pDC. Taken together, these data identifies pDC as novel source of TRANCE/RANKL in the immune system.

Death receptor 3 is essential for generating optimal protective CD4⁺ T-cell immunity against Salmonella

The TNF receptor superfamily member death receptor 3 (DR3) exacerbates Th2- and Th17-cell-mediated inflammatory and autoimmune conditions, yet no role in host defence has been reported. Here, we examined the role of DR3 during infection with Salmonella enterica serovar Typhimurium. Infection resulted in protracted expression of the DR3 ligand TL1A but not the related TNF superfamily proteins OX40L or CD30L. TL1A expression was localized to splenic F4/80(+) macrophages where S. enterica Typhimurium replicates, and temporally coincided with the onset of CD4(+) -cell expansion. To address the relevance of the TL1A-DR3 interaction, we examined immune responses to S. enterica Typhimurium in mice lacking DR3. Infected DR3(-/-) mice harboured reduced numbers of antigen-experienced and proliferating CD4(+) T cells compared with WT mice. Furthermore, the frequency of IFN-γ(+) CD4(+) T cells in DR3(-/-) mice was lower throughout the time of bacterial clearance. Importantly, bacterial clearance, which is dependent on Th1 cells, was also impaired in DR3(-/-) mice. This defect was intrinsic to CD4(+) T cells as evidenced by an increase in bacterial burden in RAG2-deficient mice receiving DR3(-/-) CD4(+) T cells compared with WT CD4(+) -cell recipients. These data establish for the first time a role for DR3 in a host defence response.

Targeting CD30/CD30L in oncology and autoimmune and inflammatory diseases

The transmembrane receptor CD30 (TNFRSF8) and its ligand CD30L (CD153, TNFSF8) are members of the tumor necrosis factor (TNF) superfamily and display restricted expression in subpopulations of activated T-and B-cells in nonpathologic conditions. CD30 expression is upregulated in various hematological malignancies, including Reed-Sternberg cells in Hodgkin's disease (HD), anaplastic large cell lymphoma (ALCL) and subsets of Non-Hodgkin's lymphomas (NHLs). Increased CD30L expression was found on mast cells within HD tumors and preclinical and clinical studies with compounds targeting the CD30/ CD30L system in HD and ALCL demonstrated therapeutic benefit. Upregulation of CD30 and CD30L is also linked to leukocytes in patients with chronic inflammatory diseases, including lupus erythematosus, asthma, rheumatoid arthritis and atopic dermatitis (AD). Preclinical studies conducted with transgenic mice or biologic compounds suggested important regulatory functions of the CD30-CD30L system in various aspects of the immune system. Such key regulatory roles and their low expression in normal conditions combined with increased expression in malignant tissues provided a strong rationale to investigate CD30 and CD30L as therapeutic targets in hematologic malignancies, autoimmune and inflammatory diseases. In this report, we review the pharmacodynamic effects of specific therapeutic compounds targeting the CD30/CD30L system in preclinical- and clinical studies.

Immune regulation by 4-1BB and 4-1BBL: complexities and challenges

SUMMARY

The tumor necrosis factor receptor family member 4-1BB plays a key role in the survival of activated and memory CD8(+) T cells. Depending on the disease model, 4-1BB can participate at different stages and influence different aspects of the immune response, likely due to the differential expression of receptor and ligand relative to other costimulatory molecules. Studies comparing mild versus severe influenza infection of mice suggest that the immune system uses inducible receptors such as 4-1BB to prolong the immune response when pathogens take longer to clear. The expression of 4-1BB on diverse cell types, evidence for bidirectional as well as receptor-independent signaling by 4-1BBL, the unexpected hyperproliferation of 4-1BB-deficient T cells, and complex effects of agonistic anti-4-1BB therapy have revealed additional roles for the 4-1BB/4-1BBL receptor/ligand pair in the immune system. In this review, we discuss these diverse roles of 4-1BB and its ligand in the immune response, exploring possible mechanisms for the observed complexities and implications for therapeutic applications of 4-1BB/4-1BBL.

Lymphoid tissue inducer cells: architects of CD4 immune responses in mice and men

In this review, we summarize the current understanding of the multiple functions of the mouse lymphoid tissue inducer (LTi) cells in: (i) the development of organized lymphoid tissue, (ii) the generation and maintenance of CD4-dependent immunity in adult lymphoid tissues; and (iii) the regulation of central tolerance in thymus. By contrast with mouse LTi cells, which have been well described, the human equivalent is only just beginning to be characterized. Human LTi-like cells expressing interleukin (IL)-22 have been identified recently and found to differentiate into natural killer (NK) cells. The relationship of LTi cells to NK cells is discussed in the light of several studies reporting a close relationship in the mouse between LTi cells and transcription factor retinoid-related orphan receptor gammat-dependent IL-22 producing NK cells in the gut. We also outline our data suggesting that these cells are present in adult human lymphoid tissues.

A novel role of CD30L/CD30 signaling by T-T cell interaction in Th1 response against mycobacterial infection

A CD30 ligand (CD30L, CD153) is a type II membrane-associated glycoprotein belonging to the TNF family. To illustrate the potential role of CD30L in CD4(+) Th1 cell responses, we investigated the fate of Ag-specific CD4(+) T cells in CD30L-deficient (CD30L(-/-)) mice after Mycobacterium bovis bacillus Calmette-Guérin (BCG) infection. The number of bacteria was significantly higher in organs of CD30L(-/-) mice than in wild-type (WT) mice 4 wk postinfection. The numbers of purified protein derivative- or Ag85B-specific-IFN-gamma-producing-CD4(+) T cells in spleen, lung, or peritoneal exudate cells were significantly fewer in CD30L(-/-) mice than in WT mice. During the infection, CD30L was expressed mainly by CD44(+)CD3(+)CD4(+) T cells but not by CD3(+)CD8(+) T cells, B cells, dendritic cells, or macrophages. Costimulation with agonistic anti-CD30 mAb or coculturing with CD30L-transfected P815 cells restored IFN-gamma production by CD4(+) T cells from BCG-infected CD30L(-/-) mice. Coculturing with CD30L(+/+)CD4(+) T cells from BCG-infected WT mice also restored the number of IFN-gamma(+)CD30L(-/-)CD4(+) T cells. When transferred into the CD30L(+/+) mice, Ag-specific donor CD30L(-/-) CD4(+) T cells capable of producing IFN-gamma were restored to the compared level seen in CD30L(+/+) CD4(+) T cells on day 10 after BCG infection. When naive CD30L(+/+) T cells were transferred into CD30L(-/-) mice, IFN-gamma-producing-CD4(+) Th1 cells of donor origin were normally generated following BCG infection, and IFN-gamma-producing-CD30L(-/-)CD4(+) Th1 cells of host origin were partly restored. These results suggest that CD30L/CD30 signaling executed by CD30(+) T-CD30L(+) T cell interaction partly play a critical role in augmentation of Th1 response capable of producing IFN-gamma against BCG infection.

Roles of embryonic and adult lymphoid tissue inducer cells in primary and secondary lymphoid tissues

The nomenclature "embryonic lymphoid tissue inducer (LTi) cell" reflects the fundamental role of the cell in secondary lymphoid tissue organization. In addition, it is equally important in primary lymphoid tissue development as it regulates central tolerance to self-antigens in the thymus. An adult LTi cell constitutively expresses two sets of tumor necrosis factor (TNF) family members, whereas its embryonic counterpart expresses only one. The first set is lymphotoxin (LT)alpha, LTbeta, and TNalpha, which are essential for the secondary lymphoid organogenesis during embryogenesis and for maintaining an organized secondary lymphoid structure during adulthood. The second set is OX40- and CD30-ligands, which are critical for memory T cell generation. Adult LTi cells regulate adaptive immune responses by providing LTbetaR signals to stromal cells to maintain secondary lymphoid tissue structure, and determine adaptive immune responses by providing OX40 and CD30 survival signals to activated T cells in memory T cell generation. Along with the consideration of the roles of embryonic LTi cells in primary and secondary lymphoid tissues, this review highlights the roles of adult LTi cells in secondary lymphoid tissue function.

Heterogeneity of lymphoid tissue inducer cell populations present in embryonic and adult mouse lymphoid tissues

Lymphoid tissue inducer (LTi) cells have a well established role in secondary lymphoid tissue development. Here, we report on the heterogeneity of LTi cells based on their CD4 and chemokine receptor expression. The CD4(-) LTi-cell population has a similar phenotype to the CD4(+) population, with similar chemokine-receptor-expressing subsets. In both embryonic and adult spleen the CD4(-) LTi-cell population is comparable as a proportion of total splenocytes to its CD4(+) counterpart. In contrast, different proportions of CD4(+) and CD4(-) LTi cells are found in different lymph nodes. Both CD4(+) and CD4(-) LTi cells share the anatomical location and are associated with vascular cell adhesion molecule-1-positive stromal cells in spleen and lymph nodes. The numbers of both CD4(+) and CD4(-) LTi cells in adult spleen are augmented in the presence of B cells. With the exception of CD4, there is a strong correlation coefficient (0.89) for gene expression between the two populations. Polymerase chain reaction analysis of individual CD4(+) and CD4(-) LTi cells shows that a similar proportion in embryonic and adult spleen co-expressed both CXCR5 and CCR7 or CXCR5 alone: 84.6% for adult CD4(+) and 87.6% for adult CD4(-); 95.3% for embryonic CD4(+) and 91.5% for embryonic CD4(-). Consistently fewer CCR7 single-positive cells were found in the CD4(+) and CD4(-) fractions in the embryo.

TNF family ligands define niches for T cell memory

Immunological memory is a critical feature of the adaptive immune system and the underlying principal behind vaccination. The mechanisms that maintain memory T cell survival between the initial and subsequent encounter with antigen remain incompletely defined. Although the cytokines IL-15 and IL-7 are important in memory T cell homeostasis, additional signals by way of TNFR family members are required for maximal maintenance of T cell memory. Here we propose a unifying model in which subsets of TNF family ligands distinguish the competitive niches for maintenance of CD4 versus CD8 T cell memory. Understanding the unique 'memory niches' defined by TNF family ligand expression will provide new insights into the mechanisms of memory T cell maintenance.