Distinct regulatory elements are required for faithful expression of human CD4 in T cells, macrophages, and dendritic cells of transgenic mice

NEF-Induced HIV-Associated Nephropathy Through HCK/LYN Tyrosine Kinases

HIV-1-associated nephropathy (HIVAN) is a severe complication of HIV-1 infection. To gain insight into the pathogenesis of kidney disease in the setting of HIV, a transgenic (Tg) mouse model [CD4C/HIV-negative regulator factor (Nef)] was used in which HIV-1 nef expression is under control of regulatory sequences (CD4C) of the human CD4 gene, thus allowing expression in target cells of the virus. These Tg mice develop a collapsing focal segmental glomerulosclerosis associated with microcystic dilatation, similar to human HIVAN. To identify kidney cells permissive to the CD4C promoter, CD4C reporter Tg lines were used. They showed preferential expression in glomeruli, mainly in mesangial cells. Breeding CD4C/HIV Tg mice on 10 different mouse backgrounds showed that HIVAN was modulated by host genetic factors. Studies of gene-deficient Tg mice revealed that the presence of B and T cells and that of several genes was dispensable for the development of HIVAN: those involved in apoptosis (Trp53, Tnfsf10, Tnf, Tnfrsf1b, and Bax), in immune cell recruitment (Ccl3, Ccl2, Ccr2, Ccr5, and Cx3cr1), in nitric oxide (NO) formation (Nos3 and Nos2), or in cell signaling (Fyn, Lck, and Hck/Fgr). However, deletion of Src partially and that of Hck/Lyn largely abrogated its development. These data suggest that Nef expression in mesangial cells through hematopoietic cell kinase (Hck)/Lck/Yes novel tyrosine kinase (Lyn) represents important cellular and molecular events for the development of HIVAN in these Tg mice.

HIV-1 Nef Induces Hck/Lyn-Dependent Expansion of Myeloid-Derived Suppressor Cells Associated with Elevated Interleukin-17/G-CSF Levels

Human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) infection causes myelodysplasia, anemia, and accumulation of inflammatory monocytes (CD14⁺ CD16⁺) through largely unknown cellular and molecular pathways. The mouse cells thought to be equivalent to human CD14⁺ CD16⁺ cells are CD11b⁺ Gr1⁺ myeloid-derived suppressor cells (MDSC). We used HIV transgenic (Tg) mouse models to study MDSC, namely, CD4C/Nef Tg mice expressing nef in dendritic cells (DC), pDC, CD4⁺ T, and other mature and immature myeloid cells and CD11c/Nef Tg mice with a more restricted expression, mainly in DC and pDC. Both Tg strains showed expansion of granulocytic and CD11b⁺ Gr1^low/int cells with MDSC characteristics. Fetal liver cell transplantation revealed that this expansion was stroma-independent and abrogated in mixed Tg/non-Tg 50% chimera. Tg bone marrow (BM) erythroid progenitors were decreased and myeloid precursors increased, suggesting an aberrant differentiation likely driving CD11b⁺ Gr1⁺ cell expansion, apparently cell autonomously in CD4C/Nef Tg mice and likely through a bystander effect in CD11c/Nef Tg mice. Hck was activated in Tg spleen, and Nef-mediated CD11b⁺ Gr1⁺ cell expansion was abrogated in Hck/Lyn-deficient Nef Tg mice, indicating a requirement of Hck/Lyn for this Nef function. IL-17 and granulocyte colony-stimulating factor (G-CSF) were elevated in Nef Tg mice. Increased G-CSF levels were normalized in Tg mice treated with anti-IL-17 antibodies. Therefore, Nef expression in myeloid precursors causes severe BM failure, apparently cell autonomously. More cell-restricted expression of Nef in DC and pDC appears sufficient to induce BM differentiation impairment, granulopoiesis, and expansion of MDSC at the expense of erythroid maturation, with IL-17→G-CSF as one likely bystander contributor. IMPORTANCE HIV-1 and SIV infection often lead to myelodysplasia, anemia, and accumulation of inflammatory monocytes (CD14⁺ CD16⁺), with the latter likely involved in neuroAIDS. We found that some transgenic (Tg) mouse models of AIDS also develop accumulation of mature and immature cells of the granulocytic lineage, decreased erythroid precursors, and expansion of MDSC (equivalent to human CD14⁺ CD16⁺ cells). We identified Nef as being responsible for these phenotypes, and its expression in mouse DC appears sufficient for their development through a bystander mechanism. Nef expression in myeloid progenitors may also favor myeloid cell expansion, likely in a cell-autonomous way. Hck/Lyn is required for the Nef-mediated accumulation of myeloid cells. Finally, we identified G-CSF under the control of IL-17 as one bystander mediator of MDSC expansion. Our findings provide a framework to determine whether the Nef>Hck/Lyn>IL-17>G-CSF pathway is involved in human AIDS and whether it represents a valid therapeutic target.

Influence of dendritic cells on B-cell responses during HIV infection

Dendritic cells (DCs) modulate B-cell differentiation, activation, and survival mainly through production of growth factors such as B lymphocyte stimulator (BLyS/BAFF). DC populations have been reported to be affected in number, phenotype and function during HIV infection and such alterations may contribute to the dysregulation of the B-cell compartment. Herein, we reflect on the potential impact of DC on the pathogenesis of HIV-related B cell disorders, and how DC status may modulate the outcome of mucosal B cell responses against HIV, which are pivotal to the control of disease. A concept that could be extrapolated to the overall outcome of HIV disease, whereby control versus progression may reside in the host's capacity to maintain DC homeostasis at mucosal sites, where DC populations present an inherent capacity of modulating the balance between tolerance and protection, and are amongst the earliest cell types to be exposed to the virus.

Adult AIDS-like disease in a novel inducible human immunodeficiency virus type 1 Nef transgenic mouse model: CD4+ T-cell activation is Nef dependent and can occur in the absence of lymphophenia

CD4C/HIV(nef) transgenic (Tg) mice express Nef in CD4+ T cells and in the cells of the macrophage/monocyte/dendritic lineage, and they develop an AIDS-like disease similar to human AIDS. In these mice, Nef is constitutively expressed throughout life. To rule out the contribution of any developmental defects caused by early expression of Nef, we generated inducible human immunodeficiency virus type 1 (HIV-1) Nef Tg mice by using the tetracycline-inducible system. Faithful expression of the Nef transgene was induced in (CD4C/rtTA x TRE/HIV(Nef)) or (CD4C/rtTA2S-M2 x TRE/HIV(Nef)) double-Tg mice upon doxycycline (DOX) treatment in drinking water. Long-term treatment of these mice with DOX also led to loss, apoptosis, and activation of CD4+ T cells, this latter phenotype being observed even with low levels of Nef. These phenotypes could be transferred by bone marrow (BM) transplantation, indicating a hematopoietic cell autonomous effect. In addition, in mixed Tg:non-Tg BM chimeras, only Tg and not non-Tg CD4+ T cells exhibited an effector/memory phenotype in the absence of lymphopenia. Finally, the DOX-induced double-Tg mice developed nonlymphoid organ diseases similar to those of CD4C/HIV(Nef) Tg mice and of humans infected with HIV-1. These results show for the first time that adult mice are susceptible to the detrimental action of Nef and that Nef-mediated T-cell activation can be independent of lymphopenia. These Tg mice represent a unique model which is likely to be instrumental for understanding the cellular and molecular pathways of Nef action as well as the main characteristics of immune reconstitution following DOX withdrawal.

Selective expression of human immunodeficiency virus Nef in specific immune cell populations of transgenic mice is associated with distinct AIDS-like phenotypes

We previously reported that CD4C/human immunodeficiency virus (HIV)(Nef) transgenic (Tg) mice, expressing Nef in CD4(+) T cells and cells of the macrophage/dendritic cell (DC) lineage, develop a severe AIDS-like disease, characterized by depletion of CD4(+) T cells, as well as lung, heart, and kidney diseases. In order to determine the contribution of distinct populations of hematopoietic cells to the development of this AIDS-like disease, five additional Tg strains expressing Nef through restricted cell-specific regulatory elements were generated. These Tg strains express Nef in CD4(+) T cells, DCs, and macrophages (CD4E/HIV(Nef)); in CD4(+) T cells and DCs (mCD4/HIV(Nef) and CD4F/HIV(Nef)); in macrophages and DCs (CD68/HIV(Nef)); or mainly in DCs (CD11c/HIV(Nef)). None of these Tg strains developed significant lung and kidney diseases, suggesting the existence of as-yet-unidentified Nef-expressing cell subset(s) that are responsible for inducing organ disease in CD4C/HIV(Nef) Tg mice. Mice from all five strains developed persistent oral carriage of Candida albicans, suggesting an impaired immune function. Only strains expressing Nef in CD4(+) T cells showed CD4(+) T-cell depletion, activation, and apoptosis. These results demonstrate that expression of Nef in CD4(+) T cells is the primary determinant of their depletion. Therefore, the pattern of Nef expression in specific cell population(s) largely determines the nature of the resulting pathological changes.

Primary human immunodeficiency virus type 1 nef alleles show major differences in pathogenicity in transgenic mice

We previously reported that the human immunodeficiency virus type 1 NL4-3 Nef is necessary and sufficient to induce a severe AIDS-like disease in transgenic (Tg) mice when the protein is expressed under the regulatory sequences of the human CD4 gene. We have now assayed additional Nef alleles (SF2, JR-CSF, YU10x, and NL4-3 [T71R] Nef alleles), including some from long-term nonprogressors (AD-93, 032an, and 039nm alleles) in the same Tg system and compared their pathogenicities. All these Nef alleles downregulated cell surface CD4 in human cells in vitro and also, with the exception of Nef(YU10x), in Tg CD4(+) T cells. Depletion of double-positive and single-positive thymocytes occurred with all alleles but was less pronounced in Nef(YU10x) Tg mice. A loss of peripheral CD4(+) T cells was observed with all alleles but was minimal in Nef(YU10x) Tg mice. In Nef(032an) and Nef(SF2) Tg mice, T-cell loss was severe despite lower levels of Tg expression, suggesting a higher virulence of these alleles. All Nef alleles except the Nef(YU10x) and Nef(NL4-3(T71R)) alleles induced an enhanced activated memory (CD25(+) CD69(+) CD44(high) CD45RB(low) CD62L(low)) and apoptotic phenotype. Also, all could interact with and/or activate PAK2 except the Nef(JR-CSF) allele. Organ (lung and kidney) diseases were present in Nef(NL4-3(T71R)), Nef(032an), Nef(039nm), and Nef(SF2) Tg mice, despite very low levels of Tg expression for the last strain. However, no organ disease or minimal organ disease developed in Nef(YU10x) and Nef(AD-93) Tg mice and Nef(JR-CSF) Tg mice, respectively, despite high levels of Tg expression. Our data show that important differences in the pathogenicities of various Nef alleles can be scored in Tg mice. Interestingly, our results also revealed that some phenotypes can segregate independently, such as CD4(+) T-cell depletion and activation, as well as severe depletion of thymic CD4(+) T cells and peripheral CD4(+) T cells. Therefore, expression of Nef alleles in Tg mice under the CD4C regulatory elements represents a novel assay for measuring their pathogenicity. Because of the very high similarity of this murine AIDS-like disease to human AIDS, this assay may have a predictive value regarding the behavior of Nef in infected humans.

Overexpression of Notch1 ectodomain in myeloid cells induces vascular malformations through a paracrine pathway

We previously reported that truncation of Notch1 (N1) by provirus insertion leads to overexpression of both the intracellular (N1(IC)) and the extracellular (N1(EC)) domains. We produced transgenic (Tg) mice expressing N1(EC) in T cells and in cells of the myeloid lineage under the regulation of the CD4 gene. These CD4C/N1(EC) Tg mice developed vascular disease, predominantly in the liver: superficial distorted vessels, cavernae, lower branching of parenchymal vessels, capillarized sinusoids, and aberrant smooth muscle/endothelial cell topography. The disease developed in lethally irradiated normal mice transplanted with Tg bone marrow or fetal liver cells as well as in Rag-/- Tg mice. In nude mice transplanted with fetal liver cells from (ROSA26 x CD4C/N1(EC)) F1 Tg mice, abnormal vessels were of recipient origin. Transplantation of Tg peritoneal macrophages into normal recipients also induced abnormal vessels. These Tg macrophages showed impaired functions, and their conditioned medium inhibited the proliferation of liver sinusoid endothelial cells in vitro. The Egr-1 gene and some of its targets (Jag1, FIII, FXIII-A, MCP-1, and MCP-5), previously implicated in hemangioma or vascular malformations, were overexpressed in Tg macrophages. These results show that myeloid cells can be reprogrammed by N1(EC) to induce vascular malformations through a paracrine pathway.

Structurally distinct ligand-binding or ligand-independent Notch1 mutants are leukemogenic but affect thymocyte development, apoptosis, and metastasis differently

We previously found that provirus insertion in T cell tumors of mouse mammary tumor virus/c-myc transgenic (Tg) mice induced two forms of Notch1 mutations. Type I mutations generated two truncated molecules, one intracellular (IC) (Notch1(IC)) and one extracellular (Notch1(EC)), while in type II mutations Notch1 was deleted of its C terminus (Notch1(DeltaCT)). We expressed these mutants in Tg mice using the CD4 promoter. Both Notch1(IC) and Notch1(DeltaCT), but not Notch1(EC), Tg mice developed double-positive (DP) thymomas. These disseminated more frequently in Notch1(DeltaCT) Tg mice. Double (Notch1(IC) x myc) or (Notch1(DeltaCT) x myc) Tg mice developed thymoma with a much shorter latency than single Tg mice, providing genetic evidence of a collaboration between these two oncogenes. FACS analysis of preleukemic thymocytes did not reveal major T cell differentiation anomalies, except for a higher number of DP cells and an accumulation of TCR(high)CD2(high)CD25(high) DP cells in Notch1(IC), and less so in Notch1(DeltaCT) Tg mice. This was associated with enhanced in vivo thymocyte proliferation. However, Notch1(IC), but not Notch1(DeltaCT), DP thymocytes were protected against apoptosis induced in vivo by dexamethasone and anti-CD3 and in vitro by anti-CD3/CD28 Abs. This indicates that the C terminus of Notch1 and/or the conserved regulation by its ligands have a significant impact on the induced T cell phenotype. Therefore, Notch1(IC) and Notch1(DeltaCT) behave as oncogenes for T cells. Because these two Notch1 mutations are very similar to those described in some forms of human T cell leukemia, these Tg mice may represent relevant models of these human leukemias.

HIV-1 Nef mutations abrogating downregulation of CD4 affect other Nef functions and show reduced pathogenicity in transgenic mice

HIV-1 Nef has the ability to downmodulate CD4 cell surface expression. Several studies have shown that CD4 downregulation is required for efficient virus replication and high infectivity. However, the pathophysiological relevance of this phenomenon in vivo, independently of its role in sustaining high virus loads, remains unclear. We studied the impact of the CD4 downregulation function of Nef on its pathogenesis in vivo, in the absence of viral replication, in the CD4C/HIV transgenic (Tg) mouse model. Two independent Nef mutants (RD35/36AA and D174K), known to abrogate CD4 downregulation, were tested in Tg mice. Flow cytometry analysis showed that downregulation of murine CD4 was severely decreased or abrogated on Tg T cells expressing respectively Nef(RD35/36AA) and Nef(D174K). Similarly, the severe depletion of double-positive CD4+CD8+ and of single-positive CD4+CD8- thymocytes, usually observed with Nef(Wt), was not detected in Nef(RD35/36AA) and Nef(D174K) Tg mice. However, both mutant Tg mice showed a partial depletion of peripheral CD4+ T cells. This was accompanied, as previously reported for Net(Wt) Tg mice, by the presence of an activated/memory-like phenotype (CD69+, CD25+, CD44+, CD45RB(Low), CD62(Low)) of CD4+ T cells expressing Nef(RD35/36AA) and to a lesser extent Nef(D174K). In addition, both mutants retained the ability to block CD4+ T cell proliferation in vitro after anti-CD3 stimulation, but not to enhance apoptosis/death of CD4+ T cells. Therefore, it appears that Nef-mediated CD4 downregulation is associated with thymic defects, but segregates independently of the activated/memory-like phenotype, of the partial depletion and of the impaired in vitro proliferation of peripheral CD4+ T cells. Histopathological assessment revealed the total absence of or decrease severity and frequency of organ AIDS-like diseases (lung, heart and kidney pathologies) in respectively Nef(RD35/36AA) and Nef(D174K) Tg mice, relative to those developing in Nef(Wt) Tg mice. Our data suggest that the RD35/36AA and D174K mutations affect other Nef functions, namely those involved in the development of lung and kidney diseases, in addition to their known role in CD4 downregulation. Similarly, in HIV-1-infected individuals, loss of CD4 downregulation by Nef alleles may reflect their lower intrinsic pathogenicity, independently of their effects on virus replication.

Expression of HIV-1 genes in podocytes alone can lead to the full spectrum of HIV-1-associated nephropathy

BACKGROUND

Human immunodeficiency virus (HIV)-1-associated nephropathy (HIVAN) is characterized by collapsing focal and segmental glomerulosclerosis (FSGS) and microcystic tubular dilatation. HIV-1 infection is also associated with other forms of nephropathy, including mesangial hyperplasia. Since HIV-1 gene products are detected in podocytes and other renal cells, it remains uncertain whether podocyte-restricted HIV-1 gene expression can account for the full spectrum of renal lesions involving nonpodocytes.

METHODS

To define the role of podocyte-restricted HIV-1 gene expression in the progression of HIVAN, we generated transgenic mice that express nonstructural HIV-1 genes selectively in podocytes.

RESULTS

Four of the seven founder mice developed proteinuria and nephropathy. In a subsequently established transgenic line, reverse transcription-polymerase chain reaction (RT-PCR) analysis detected mRNAs for vif, vpr, nef, and spliced forms of tat and rev, but not vpu, in the kidney. In situ hybridization localized HIV-1 RNA to the podocyte. Transgenic mice on FVB/N genetic background exhibited cuboidal morphology of podocytes with reduced extension of primary and foot processes at 2 weeks of age. After 3 weeks of age, these mice developed massive and nonselective proteinuria with damage of podocytes and other glomerular cells and, after 4 weeks of age, collapsing FSGS and microcystic tubular dilatation. In marked contrast, transgenic mice with C57BL/6 genetic background showed either normal renal histology or only mild mesangial expansion without overt podocyte damage.

CONCLUSION

The present study demonstrates that podocyte-restricted expression of HIV-1 gene products is sufficient for the development of collapsing glomerulosclerosis in the setting of susceptible genetic background.

The Nef-mediated AIDS-like disease of CD4C/human immunodeficiency virus transgenic mice is associated with increased Fas/FasL expression on T cells and T-cell death but is not prevented in Fas-, FasL-, tumor necrosis factor receptor 1-, or interleukin-1beta-converting enzyme-deficient or Bcl2-expressing transgenic mice

CD4(+)- and CD8(+)-T-cell death is a frequent immunological dysfunction associated with the development of human AIDS. We studied a murine model of AIDS, the CD4C/HIV transgenic (Tg) mouse model, to assess the importance of the apoptotic pathway in human immunodeficiency virus type 1 (HIV-1) pathogenesis. In these Tg mice, Nef is the major determinant of the disease and is expressed in immature and mature CD4(+) T cells and in cells of the macrophage/myeloid lineage. We report here a novel AIDS-like phenotype: enhanced death, most likely by apoptosis (as assessed by 7-aminoactinomycin D and annexin V/propidium iodide staining), of Tg thymic and peripheral CD4(+) and CD8(+) T cells. The Tg CD4(+) and CD8(+) T cells were also more susceptible to cell death after activation in vitro in mixed lymph node (LN) cultures. However, activation-induced cell death was not higher in Tg than in non-Tg-purified CD4(+) T cells. In addition, expression of Fas and FasL, assessed by flow cytometry, was increased in CD4(+) and CD8(+) T cells from Tg mice compared to that of non-Tg littermates. Despite the enhanced expression of Fas and FasL on Tg CD4(+) and CD8(+) T cells, Fas (lpr/lpr) and FasL (gld/gld) mutant CD4C/HIV Tg mice developed an AIDS-like disease indistinguishable from lpr/+ and gld/+ CD4C/HIV Tg mice, including loss of CD4(+) T cells. Similarly, CD4C/HIV Tg mice homozygous for mutations of two other genes implicated in cell death (interleukin-1beta-converting enzyme [ICE], tumor necrosis factor receptor 1 [TNFR-1]) developed similar AIDS-like disease as their respective heterozygous controls. Moreover, the double-Tg mice from a cross between the Bcl2/Wehi25 and CD4C/HIV Tg mice showed no major protection against disease. These results represent genetic evidence for the dispensable role of Fas, FasL, ICE, and TNFR-1 on the development of both T-cell loss and organ disease of these Tg mice. They also provide compelling evidence on the lack of protection by Bcl2 against Tg CD4(+)-T-cell death. In view of the high resemblance between numerous phenotypes observed in the CD4C/HIV Tg mice and in human AIDS, our findings are likely to be relevant for the human disease.

Treating haemophilia A with recombinant blood factors: a comparison

The mainstay in the treatment of haemophilia A is replacement therapy with repeated infusions of plasma-derived Factor VIII (FVIII) concentrates or recombinant FVIII products. While modern plasma-derived FVIII concentrates have an excellent safety profile, there is an inexorable shift towards the use of recombinant products, especially in affluent countries. Recombinant FVIII products have demonstrated excellent haemostatic efficacy and higher safety with regard to the transmission of blood-borne pathogens. The experience in haemophilia A treatment with five currently available recombinant FVIII products, including the first third-generation product, Advate, which is completely free from human or animal proteins, is summarised. Some unresolved problems concerning the efficacy and assaying of recombinant factors and future perspectives of both recombinant and plasma-derived FVIII products in global haemophilia care, are also discussed.

Meta-analytic evidence of increased breakthrough bleeding during prophylaxis with B-domain deleted factor VIII

A recent meta-analysis of 13 observational studies suggested reduced haemostatic efficacy during prophylaxis and shortened half-life of B-domain deleted factor VIII (BDD-rFVIII) as compared with full-length factor VIII (FL-FVIII). The meta-analysis included a multivariate model that took both dose and age into account. In addition, several assumptions and interpretations were required in order to conduct the meta-analysis. It is important to test the impact of such assumptions and interpretations through sensitivity analysis. In the published meta-analysis, results of several sensitivity analyses were described involving the effect of study design; heterogeneity of subjects in some studies; type of assay used for half-life determinations; and year of publication. In two subsequent brief reports, additional sensitivity analyses addressed choice of median-to-mean conversion factor over a wide range of scenarios and use of age at start of prophylaxis vs mean age during prophylaxis in the multivariate model. A recognized inherent difficulty in the meta-analysis of multiple published reports from similar studies is the possibility of some subject or data overlap. Therefore, the present communication details further sensitivity analyses encompassing assumptions regarding the possibility of subject duplication in a subgroup of subjects from one study and possible duplication of pharmacokinetic data from two smaller studies within the reports of two larger studies. All the sensitivity analyses support the main conclusions of the meta-analysis, namely, that BDD-rFVIII substantially increases the risk of breakthrough bleeding during prophylaxis, possibly at least partly because of shorter half-life than that of FL-FVIII.

In vivo mutational analysis of the N-terminal region of HIV-1 Nef reveals critical motifs for the development of an AIDS-like disease in CD4C/HIV transgenic mice

HIV-1 Nef is a critical determinant of pathogenicity in humans and transgenic (Tg) mice. To gain a better understanding of the molecular mechanisms by which Nef induces an AIDS-like disease in Tg mice, a mutational analysis of the N-terminal domain, involved in anchoring Nef to the plasma membrane, was carried out. The pathogenic effects of these Nef mutant alleles were evaluated in Tg mice by FACS analysis and by histopathological assessment. Mutation of the myristoylation site (G2A) completely abrogated the development of the AIDS-like organ disease in Tg mice, although partial downregulation of the CD4 cell surface protein and depletion of peripheral CD4+ T-cells, but not of CD4(+)CD8+ thymocytes, still occurred. Despite that, the peripheral CD4+ T cells expressing Nef(G2A) show normal spontaneous proliferation in vivo or after stimulation in vitro, including in an allogenic mixed leukocyte reaction (MLR). Three other internal deletion mutants of Nef, spanning amino acids 8-17 (Nef(Delta8-17)), 25-35 (Nef(Delta25-35)), and 57-66 (Nef(Delta57-66)), were also studied. Nef(Delta8-17) retained full pathogenic potential, although Nef(Delta25-35) and Nef(Delta57-66) Tg mice were free of organ disease. However, Nef(Delta25-35) Tg mice exhibited disorganization of thymic architecture and a partial depletion of peripheral CD4+ T cells. These data indicate that myristoylation and other regions at the N-terminus of Nef (aa 25-35 and 57-66) are involved in mediating severe T-cell phenotypes and organ disease, although residues 8-17 are dispensable for these Nef functions. In addition, these results indicate that at least some of the CD4+ T-cell phenotypes can develop independently of the other AIDS-like organ phenotypes. This apparent segregation of different Nef-mediated phenotypes suggests distinct mechanisms of Nef action in different populations of target cells, and may be relevant to human AIDS.

Immunopathogenesis of oropharyngeal candidiasis in human immunodeficiency virus infection

Oropharyngeal and esophageal candidiases remain significant causes of morbidity in human immunodeficiency virus (HIV)-infected patients, despite the dramatic ability of antiretroviral therapy to reconstitute immunity. Notable advances have been achieved in understanding, at the molecular level, the relationships between the progression of HIV infection, the acquisition, maintenance, and clonality of oral candidal populations, and the emergence of antifungal resistance. However, the critical immunological defects which are responsible for the onset and maintenance of mucosal candidiasis in patients with HIV infection have not been elucidated. The devastating impact of HIV infection on mucosal Langerhans' cell and CD4(+) cell populations is most probably central to the pathogenesis of mucosal candidiasis in HIV-infected patients. However, these defects may be partly compensated by preserved host defense mechanisms (calprotectin, keratinocytes, CD8(+) T cells, and phagocytes) which, individually or together, may limit Candida albicans proliferation to the superficial mucosa. The availability of CD4C/HIV transgenic mice expressing HIV-1 in immune cells has provided the opportunity to devise a novel model of mucosal candidiasis that closely mimics the clinical and pathological features of candidal infection in human HIV infection. These transgenic mice allow, for the first time, a precise cause-and-effect analysis of the immunopathogenesis of mucosal candidiasis in HIV infection under controlled conditions in a small laboratory animal.

The AIDS-like disease of CD4C/human immunodeficiency virus transgenic mice is associated with accumulation of immature CD11bHi dendritic cells

CD4C/human immunodeficiency virus (HIV) transgenic mice develop an AIDS-like disease. We used this model to study the effects of HIV-1 on dendritic cells (DC). We found a progressive decrease in total DC numbers in the lymph nodes, with a significant accumulation of CD11b(Hi) DC. In the thymus, the recovery of transgenic CD8alpha(+) DC had a tendency to be lower. Spleen DC were augmented in the marginal zone. Transgenic DC showed a decreased capacity to present antigen in vitro, consistent with their reduced major histocompatibility complex class II expression and impaired maturation profile. The accumulation of immature DC may contribute to disease and may reflect an adaptive advantage for the virus by favoring its replication and preventing the generation of fully functional antiviral responses.

Cardiac disease in transgenic mice expressing human immunodeficiency virus-1 nef in cells of the immune system

We previously reported that a severe acquired immune deficiency syndrome-like disease develops in transgenic (Tg) mice expressing the human immunodeficiency virus-1 in its natural target cells: immature and mature CD4(+) T cells and cells of the macrophage/dendritic lineage. Here, we show that these mice also develop cardiac disease, characterized most prominently by a focal myocytolysis, occasionally by myocarditis and by deposition of endogenous immunoglobulin on cardiomyocytes. Microfil perfusion demonstrated widespread coronary arteriospasm and echocardiographic analysis revealed depressed cardiac function in Tg mice. A higher (but still modest) level of cardiomyocyte apoptosis was detected in Tg as compared to non-Tg hearts. Tg expression was detected in some of the infiltrating mononuclear cells, but not in cardiomyocytes or in cells of the heart vessels, suggesting a human immunodeficiency virus-1-induced disease process mediated by cells of the immune system. The similarity of the heart disease observed in these Tg mice to that observed in acquired immune deficiency syndrome patients suggests a common pathogenesis.

Expression of simian immunodeficiency virus nef in immune cells of transgenic mice leads to a severe AIDS-like disease

In order to study the functions of simian immunodeficiency virus (SIV) Nef in vivo in a small-animal model, we constructed transgenic (Tg) mice expressing the SIV(mac)239 nef gene in the natural target cells of the virus under the control of the human CD4 gene promoter (CD4C). These CD4C/SHIV-nef(SIV) Tg mice develop a severe AIDS-like disease, with manifestations including premature death, failure to thrive or weight loss, wasting, thymic atrophy, an especially low number of peripheral CD8+ T cells as well as a low number of peripheral CD4+ T cells, diarrhea, splenomegaly, and kidney (interstitial nephritis, segmental glomerulosclerosis), lung (lymphocytic interstitial pneumonitis), and heart disease. In addition, these Tg mice fail to mount a class-switched antibody response after immunization with ovalbumin, they produce anti-DNA autoantibodies, and some of them develop Pneumocystis carinii lung infections. All these results suggest a generalized Nef-induced immunodeficiency. The low numbers of peripheral CD8+ and CD4+ T cells are likely to reflect a thymic defect and may be similar to the DiGeorge-like "thymic defect" immunophenotype described for a subgroup of human immunodeficiency virus type 1-infected children. Therefore, it appears that SIV Nef alone expressed in mice, in appropriate cell types and at sufficient levels, can elicit many of the phenotypes of simian and human AIDS. These Tg mice should be instrumental in studying the pathogenesis of SIV Nef-induced phenotypes.