A group of T cells recognizes glycolipids presented by molecules of the CD1 family. The CD1d-restricted natural killer T cells (NKT cells) are primarily considered to be self-reactive. By employing CD1d-binding and T cell assays, the following structural parameters for presentation by CD1d were defined for a number of mycobacterial and mammalian lipids: two acyl chains facilitated binding, and a polar head group was essential for T cell recognition. Of the mycobacterial lipids tested, only a phosphatidylinositol mannoside (PIM) fulfilled the requirements for CD1d binding and NKT cell stimulation. This PIM activated human and murine NKT cells via CD1d, thereby triggering antigen-specific IFN-␥ production and cell-mediated cytotoxicity, and PIM-loaded CD1d tetramers identified a subpopulation of murine and human NKT cells. This phospholipid, therefore, represents a mycobacterial antigen recognized by T cells in the context of CD1d. I n contrast to classical MHC molecules, the nonpolymorphic CD1 proteins present lipid antigens to T cells (1). These evolutionaryconserved antigen-presenting molecules are divided into group I (consisting of CD1a, CD1b, CD1c, and CD1e in humans) and group II (represented by CD1d in mice and humans) (2, 3). CD1 molecules are 43-to 49-kDa cell-surface glycoproteins homologous to MHC class I molecules with a limited allelic polymorphism (4). Compared with MHC class I, they possess a deeper and more hydrophobic antigen-binding groove. Human CD1a, CD1b, and CD1c present mammalian and mycobacterial lipids to CD4 and CD8 T cells (2, 5). CD1d-restricted T cells appear to be primarily self-reactive, and they have been implicated in the control of autoimmune diseases (6, 7). The marine sponge-derived lipid ␣-galactosylceramide (␣-GalCer), in the context of CD1d, is a potent stimulator of all V␣14-J␣281 T cell receptor (TCR)-expressing natural killer T cells (NKT cells) in mice and their cognates in humans expressing V␣24-J␣Q TCR. Therefore, although ␣-GalCer is an artificial ligand of unclear physiological relevance, this lipid is a useful tool to study CD1d-restricted NKT cells in mammals (8, 9). The NKT cell subset is considered to perform regulatory, rather than host-defense, functions with the following two self antigens identified so far: phosphatidylinositol (PI) and the tumor-associated disialoganglioside GD3 (10, 11). To our knowledge, no bacterial antigen has been identified, which is presented by CD1d.In analyzing the structural determinants of mycobacterial and mammalian lipids for binding to CD1d and recognition by T cells, we identified a PI mannoside (PIM), which induced IFN-␥ release and cytotoxicity in a CD1d-restricted manner, from the mycobacterial cell wall. Hence, this PIM is a bacterial antigen for human and murine NKT cells. Materials and MethodsChemicals. All reagents were purchased from Sigma, unless indicated otherwise. ␣-GalCer was kindly provided by Pharmaceutical Research Laboratories (Kirin Brewery, Gumna, Japan).Mice. All mice were bred and housed under specific pat...

Mycobacterium tuberculosis remains one of the top microbial killers of humans causing ∼2 million deaths annually. More than 90% of the 2 billion individuals infected never develop active disease, indicating that the immune system is able to generate mechanisms that control infection. However, the immune response generally fails to achieve sterile clearance of bacilli. Using adoptive cell transfer into C57BL/6J-Rag1tm1Mom mice (Rag1−/−), we show that regulatory T cells prevent eradication of tubercle bacilli by suppressing an otherwise efficient CD4+ T cell response. This protective CD4+ T cell response was not correlated with increased numbers of IFN-γ- or TNF-α-expressing cells or general expression levels of IFN-γ or inducible NO synthase in infected organs compared with wild-type C57BL/6 animals. Furthermore, suppression of protection by cotransferred regulatory T cells was neither accompanied by a general increase of IL-10 expression nor by higher numbers of IL-10-producing CD4+ T cells.

CD4+ T cell help is important for the generation of CD8+ T cell responses. We used depleting anti-CD4 mAb to analyze the role of CD4+ T cells for memory CD8+ T cell responses after secondary infection of mice with the intracellular bacterium Listeria monocytogenes, or after boost immunization by specific peptide or DNA vaccination. Surprisingly, anti-CD4 mAb treatment during secondary CD8+ T cell responses markedly enlarged the population size of antigen-specific CD8+ T cells. After boost immunization with peptide or DNA, this effect was particularly profound, and antigen-specific CD8+ T cell populations were enlarged at least 10-fold. In terms of cytokine production and cytotoxicity, the enlarged CD8+ T cell population consisted of functional effector T cells. In depletion and transfer experiments, the suppressive function could be ascribed to CD4+CD25+ T cells. Our results demonstrate that CD4+ T cells control the CD8+ T cell response in two directions. Initially, they promote the generation of a CD8+ T cell responses and later they restrain the strength of the CD8+ T cell memory response. Down-modulation of CD8+ T cell responses during infection could prevent harmful consequences after eradication of the pathogen.

Infection of mice with the intracellular bacterium Listeria monocytogenes results in a strong CD8+ T cell response that is critical for efficient control of infection. We used CD28-deficient mice to characterize the function of CD28 during Listeria infection, with a main emphasis on Listeria-specific CD8+ T cells. Frequencies and effector functions of these T cells were determined using MHC class I tetramers, single cell IFN-γ production and Listeria-specific cytotoxicity. During primary Listeria infection of CD28−/− mice we observed significantly reduced numbers of Listeria-specific CD8+ T cells and only marginal levels of specific IFN-γ production and cytotoxicity. Although frequencies were also reduced in CD28−/− mice during secondary response, we detected a considerable population of Listeria-specific CD8+ T cells in these mice. In parallel, IFN-γ production and cytotoxicity were observed, revealing that Listeria-specific CD8+ T cells in CD28−/− mice expressed normal effector functions. Consistent with their impaired CD8+ T cell activation, CD28−/− mice suffered from exacerbated listeriosis both after primary and secondary infection. These results demonstrate participation of CD28 signaling in the generation and expansion of Ag-specific CD8+ T cells in listeriosis. However, Ag-specific CD8+ T cells generated in the absence of CD28 differentiated into normal effector and memory T cells.

CD8؉ T-cells are a major source for the production of non-cytolytic factors that inhibit HIV-1 replication. In order to characterize further these factors, we analyzed gene expression profiles of activated CD8؉ T-cells using a human cDNA expression array containing 588 human cDNAs. mRNA for the chemokine I-309 (CCL1), the cytokines granulocyte-macrophage colony-stimulating factor and interleukin-13, and natural killer cell enhancing factors (

The immune response against the intracellular bacterium Listeria monocytogenes involves both CD4+ and CD8+ T cells. We used the MHC class II-presented peptide listeriolysin189–201 to characterize the organ-specific CD4+ T cell response during infection. Systemic listeriosis resulted in a strong peptide-specific CD4+ T cell response with frequencies of 1/100 and 1/30 CD4+ splenocytes at the peak of primary and secondary response, respectively. This response was not restricted to lymphoid organs, because we detected specific CD4+ T cells in all tissues analyzed. However, the tissue distribution of the T cell response was dependent on the route of infection. After i.v. infection, the strongest CD4+ T cell response and the highest levels of memory cells were observed in spleen and liver, the major sites of L. monocytogenes replication. After oral infection, we detected a strong response in the liver, the lamina propria, and the intestinal epithelium. These tissues also harbored the highest frequencies of listeriolysin189–201-specific CD4+ memory T cells 5–8 wk post oral infection. Our results show that kinetics and magnitude of the CD4+ T cell response and the accumulation of CD4+ memory T cells depend on the route of infection and are regulated in a tissue-specific way.

Effective priming of T cell responses depends on cognate interactions between naive T cells and professional antigen-presenting cells (APCs). This contact is the result of highly coordinated migration processes, in which the chemokine receptor CCR7 and its ligands, CCL19 and CCL21, play a central role. We used the murine Listeria monocytogenes infection model to characterize the role of the CCR7/CCR7 ligand system in the generation of T cell responses during bacterial infection. We demonstrate that efficient priming of naive major histocompatibility complex (MHC) class Ia–restricted CD8+ T cells requires CCR7. In contrast, MHC class Ib–restricted CD8+ T cells and MHC class II–restricted CD4+ T cells seem to be less dependent on CCR7; memory T cell responses are independent of CCR7. Infection experiments with bone marrow chimeras or mice reconstituted with purified T cell populations indicate that CCR7 has to be expressed on CD8+ T cells and professional APCs to promote efficient MHC class Ia–restricted T cell priming. Thus, different T cell subtypes and maturation stages have discrete requirements for CCR7.

Tuberculosis causes 2 million deaths per year, yet in most cases the immune response successfully contains the infection and prevents disease outbreak. Induced lymphoid structures associated with pulmonary granuloma are observed during tuberculosis in both humans and mice and could orchestrate host defense. To investigate whether granuloma perform lymphoid functions, mice lacking secondary lymphoid organs (SLO) were infected with Mycobacterium tuberculosis (MTB). As in WT mice, granuloma developed, exponential growth of MTB was controlled, and antigen-specific T-cell responses including memory T cells were generated in the absence of SLO. Moreover, adoptively transferred T cells were primed locally in lungs in a granuloma-dependent manner. T-cell activation was delayed in the absence of SLO, but resulted in a normal development program including protective subsets and functional recall responses that protected mice against secondary MTB infection. Our data demonstrate that protective immune responses can be generated independently of SLO during MTB infection and implicate local pulmonary T-cell priming as a mechanism contributing to host defense.Key words: Granuloma . Lymphoid neogenesis . T-cell development . Tuberculosis Supporting Information available online IntroductionMycobacterium tuberculosis (MTB), the causative agent of tuberculosis (TB), currently persists in one-third of the world's population [1]. In most cases, the immune response generated upon exposure contains, but does not eradicate, the bacilli and an asymptomatic persistent infection develops, termed latent TB. Approximately one in ten latently infected individuals undergo reactivation to active TB disease during their lifetime. However, Ã These authors contributed equally to this work. ÃÃ These authors share equal senior authorship. [2,3]. Granuloma are considered central for control of MTB as loss of granuloma structure is associated with poor disease outcome in humans and animal models [3,4]. Yet, the precise mechanisms by which granuloma mediate control of MTB are poorly understood. Induction of an adaptive immune response is essential for host protection against MTB. Antigen-specific T-cell responses are generated within secondary lymphoid organs (SLO), such as lymph nodes (NO) and spleen. SLO maximize efficiency of encounters between APC and naïve T lymphocytes [5]. Therefore, SLO are critical for the generation of adaptive immunity. Ectopic accumulations of lymphoid cells, known as tertiary lymphoid organs, sometimes arise during chronic inflammation or infection. Tertiary lymphoid organs resemble SLO in structure and cell composition and evidence exists that some are capable of generating adaptive immunity [5,6]. However, whether immune responses generated outside of SLO are truly effective and thus beneficial in defense against pathogens is unclear.Recent reports have described lymphoid features associated with murine and human granuloma, such as B-cell follicles and the peripheral node addressin, which is expressed on high endothel...