Cell-mediated (type-1) immunity is necessary for immune protection against most intracellular pathogens and, when excessive, can mediate organ-specific autoimmune destruction. Mice deficient in Eta-1 (also called osteopontin) gene expression have severely impaired type-1 immunity to viral infection [herpes simplex virus-type 1 (KOS strain)] and bacterial infection (Listeria monocytogenes) and do not develop sarcoid-type granulomas. Interleukin-12 (IL-12) and interferon-gamma production is diminished, and IL-10 production is increased. A phosphorylation-dependent interaction between the amino-terminal portion of Eta-1 and its integrin receptor stimulated IL-12 expression, whereas a phosphorylation-independent interaction with CD44 inhibited IL-10 expression. These findings identify Eta-1 as a key cytokine that sets the stage for efficient type-1 immune responses through differential regulation of macrophage IL-12 and IL-10 cytokine expression.

Tuberculosis (TB) and HIV co-infections place an immense burden on health care systems and pose particular diagnostic and therapeutic challenges. Infection with HIV is the most powerful known risk factor predisposing for Mycobacterium tuberculosis infection and progression to active disease, which increases the risk of latent TB reactivation 20-fold. TB is also the most common cause of AIDS-related death. Thus, M. tuberculosis and HIV act in synergy, accelerating the decline of immunological functions and leading to subsequent death if untreated. The mechanisms behind the breakdown of the immune defense of the co-infected individual are not well known. The aim of this review is to highlight immunological events that may accelerate the development of one of the two diseases in the presence of the co-infecting organism. We also review possible animal models for studies of the interaction of the two pathogens, and describe gaps in knowledge and needs for future studies to develop preventive measures against the two diseases.

CD8+ T cell exhaustion represents a major hallmark of chronic HIV infection. Two key transcription factors governing CD8+ T cell differentiation, T-bet and Eomesodermin (Eomes), have previously been shown in mice to differentially regulate T cell exhaustion in part through direct modulation of PD-1. Here, we examined the relationship between these transcription factors and the expression of several inhibitory receptors (PD-1, CD160, and 2B4), functional characteristics and memory differentiation of CD8+ T cells in chronic and treated HIV infection. The expression of PD-1, CD160, and 2B4 on total CD8+ T cells was elevated in chronically infected individuals and highly associated with a T-betdimEomeshi expressional profile. Interestingly, both resting and activated HIV-specific CD8+ T cells in chronic infection were almost exclusively T-betdimEomeshi cells, while CMV-specific CD8+ T cells displayed a balanced expression pattern of T-bet and Eomes. The T-betdimEomeshi virus-specific CD8+ T cells did not show features of terminal differentiation, but rather a transitional memory phenotype with poor polyfunctional (effector) characteristics. The transitional and exhausted phenotype of HIV-specific CD8+ T cells was longitudinally related to persistent Eomes expression after antiretroviral therapy (ART) initiation. Strikingly, these characteristics remained stable up to 10 years after ART initiation. This study supports the concept that poor human viral-specific CD8+ T cell functionality is due to an inverse expression balance between T-bet and Eomes, which is not reversed despite long-term viral control through ART. These results aid to explain the inability of HIV-specific CD8+ T cells to control the viral replication post-ART cessation.

The biological phenotype of primary human immunodeficiency virus type 1 (HIV-1) isolates varies according to the severity of the HIV infection. Here we show that the two previously described groups of rapid/high, syncytium-inducing (SI) and slow/low, non-syncytium-inducing (NSI) isolates are distinguished by their ability to utilize different chemokine receptors for entry into target cells. Recent studies have identified the C-X-C chemokine receptor CXCR4 (also named fusin or Lestr) and the CC chemokine receptor CCR5 as the principal entry cofactors for T-cell-line-tropic and non-T-cell-line-tropic HIV-1, respectively. Using U87.CD4 glioma cell lines, stably expressing the chemokine receptor CCR1, CCR2b, CCR3, CCR5, or CXCR4, we have tested chemokine receptor specificity for a panel of genetically diverse envelope glycoprotein genes cloned from primary HIV-1 isolates and have found that receptor usage was closely associated with the biological phenotype of the virus isolate but not the genetic subtype. We have also analyzed a panel of 36 well-characterized primary HIV-1 isolates for syncytium induction and replication in the same series of cell lines. Infection by slow/low viruses was restricted to cells expressing CCR5, whereas rapid/high viruses could use a variety of chemokine receptors. In addition to the regular use of CXCR4, many rapid/high viruses used CCR5 and some also used CCR3 and CCR2b. Progressive HIV-1 infection is characterized by the emergence of viruses resistant to inhibition by ␤-chemokines, which corresponded to changes in coreceptor usage. The broadening of the host range may even enable the use of uncharacterized coreceptors, in that two isolates from immunodeficient patients infected the parental U87.CD4 cell line lacking any engineered coreceptor. Two primary isolates with multiple coreceptor usage were shown to consist of mixed populations, one with a narrow host range using CCR5 only and the other with a broad host range using CCR3, CCR5, or CXCR4, similar to the original population. The results show that all 36 primary HIV-1 isolates induce syncytia, provided that target cells carry the particular coreceptor required by the virus.

The osteopontin (Opn) glycoprotein has been implicated in diverse physiological processes, including vascularization, bone formation, and inflammatory responses. Studies of its role in immune responses has suggested that Opn can set the early stage of type-1 immune (cell-mediated) responses through differential regulation of IL-12 and IL-10 cytokine gene expression in macrophages. Although Opn has been suggested to play a role in the development of type-1 immunity, little is known about control of Opn gene expression. Here, we report that Opn gene expression in activated T cells, but not macrophages, is regulated by T-bet, a transcription factor that controls CD4 ؉ T helper (Th1) cell lineage commitment. We also find that T-bet-dependent expression of Opn in T cells is essential for efficient skewing of CD4 ؉ T and CD8 ؉ T cells toward the Th1 and type 1 CD8 ؉ T cells (Tc1) pathway, respectively. Taken together, these findings begin to delineate the genetic basis of Opn expression in T cells and further clarify the role of Opn in Th and Tc1 development.genetic programming ͉ T helper 1 development ͉ type-1 immune response T he osteopontin (Opn) glycoprotein has been independently identified and studied by investigators from numerous scientific fields in view of its role in immune responses, vascularization, and bone formation through interactions with mononuclear, endothelial, and bone cells, respectively. Analysis of its contribution to immune responses has suggested that Opn expression can set the stage for protective type-1 immune responses after viral and bacterial infection through differential regulation of IL-12 and IL-10 cytokine production (1-3).Studies of Opn-deficient (Opn Ϫ/Ϫ ) mice have indicated that Opn contributes to host resistance against diverse microbial pathogens including herpes simplex virus 1, Listeria monocytogenes (4), and rotavirus (5). Opn expression is also essential for effective Th1-dependent granuloma formation and a positive clinical outcome in patients suffering from mycobacterial infection (6), whereas ectopic Opn expression has been implicated in the granulomatous lesions of Crohn's disease (7). Dysregulated Opn expression has also been implicated in several autoimmune disorders, including murine experimental autoimmune encephalomyelitis (EAE) (8, 9), multiple sclerosis (10), rheumatoid arthritis (11), and atherosclerosis (12, 13). Dysregulated Opn expression has been correlated with excessive Th1 polarization of CD4 ϩ T cells in these disorders (7,14) opening the possibility that Opn gene expression may directly contribute to Th1͞type 1 CD8 ϩ T cells (Tc1) genetic programming. However, the genetic basis of Opn expression in Th-cell subsets is not well understood.T-bet, a member of the T box family of transcription factors, is the master coordinator of gene expression in T cells that initiate type-1 immunity and is essential for Th1 cell polarization (15). Thus, T-bet deficiency reduces IFN-␥ production by activated CD4 ϩ T cells and T cell antigen receptor (TCR)-transgenic CD8...

Recent studies indicate that early T lymphocyte activation 1 (Eta-1), also known as osteopontin, is a cytokine contributing to the development of Th1 immunity. In the present report, the role of Eta-1 in experimental autoimmune encephalomyelitis (EAE), a disease associated with Th1 immunity, was examined by analysis of disease progression in Eta-1-deficient (Eta-1−/−) mice. Although incidence and onset of peptide-induced EAE were found to be similar in Eta-1−/− and Eta-1+/+ mice, Eta-1−/− mice displayed significantly lower mean maximal clinical score and faster recovery without spontaneous relapses. Accordingly, decreased inflammatory infiltration and demyelination were observed in the spinal cords of Eta-1−/− mice. Furthermore, in comparison to Eta-1+/+, Eta-1−/− CD4+ T cells had reduced expression of IFN-γ and TNF-α upon ex vivo restimulation. Taken together, these results suggest that Eta-1 may sustain autoimmune responses by assisting in maintenance of Th1 immunity during EAE.

The evolution of human immunodeficiency virus type 1 (HIV-1) coreceptor use has been described as the acquisition of CXCR4 use linked to accelerated disease progression. However, CXCR4-using virus can be isolated only from approximately one-half of individuals with progressive HIV-1 disease. The other half continue to yield only CCR5-using viruses (R5 phenotype) throughout the course of disease. In the present work, the use of receptor chimeras between CCR5 and CXCR4 allowed us to study the evolution of HIV-1 with the R5 phenotype, which was not revealed by studies of wild-type coreceptor use. All together, 246 isolates (173 with the R5 phenotype) from 31 individuals were tested for their ability to infect cells through receptor chimeras. R5 narrow virus was able to use only wild-type CCR5, whereas R5 broad(1) to R5 broad(3) viruses were able to use one to three chimeric receptors, respectively. Broad use of chimeric receptors was interpreted as an increased flexibility in the mode of receptor use. R5 broad isolates showed higher infectivity in cells expressing wild-type CCR5 than R5 narrow isolates. Also, the increased flexibility of R5 broad isolates was concomitant with a lower sensitivity to inhibition by the CC chemokine RANTES. Our results indicate a close relationship between HIV-1 phenotypic changes and the pathogenic process, since the mode and efficiency of CCR5 use as well as the decrease in the RANTES sensitivities of isolated viruses are significantly correlated with CD4؉ -T-cell decline in a patient. One possible explanation is that ligand competition at the CCR5 receptor or changed CCR5 availability may shape the outcome of HIV-1 infection.

Primary HIV-1 isolates were evaluated for their sensitivity to inhibition by ␤-chemokines RANTES (regulated upon activation, normal T-cell expressed and secreted), macrophage inflammatory protein 1␣ (MIP-1␣), and MIP-1␤. Virus isolates of both nonsyncytium-inducing (NSI) and syncytium-inducing (SI) biological phenotypes recovered from patients at various stages of HIV-1 infection were assessed, and the results indicated that only the isolates with the NSI phenotype were substantially inhibited by the ␤-chemokines. More important to note, these data demonstrate that resistance to inhibition by ␤-chemokines RANTES, MIP-1␣, and MIP-1␤ is not restricted to T cell line-adapted SI isolates but is also a consistent property among primary SI isolates. Analysis of isolates obtained sequentially from infected individuals in whom viruses shifted from NSI to SI phenotype during clinical progression exhibited a parallel loss of sensitivity to ␤-chemokines. Loss of virus sensitivity to inhibition by ␤-chemokines RANTES, MIP-1␣, and MIP-1␤ was furthermore associated with changes in the third variable (V3) region amino acid residues previously described to correlate with a shift of virus phenotype from NSI to SI. Of interest, an intermediate V3 genotype correlated with a partial inhibition by the ␤-chemokines. In addition, we also identified viruses sensitive to RANTES, MIP-1␣, and MIP-1␤ of NSI phenotype that were isolated from individuals with AIDS manifestations, indicating that loss of sensitivity to ␤-chemokine inhibition and shift in viral phenotype are not necessarily prerequisites for the pathogenesis of HIV-1 infection.