HIV antigen-induced release of histamine from basophils from HIV infected patients. Mechanism and relation to disease progression and immunodeficiency

A novel humanized mouse model for HIV and tuberculosis co-infection studies

Background

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), continues to be a major public health problem worldwide. The human immunodeficiency virus (HIV) is another equally important life-threatening pathogen. HIV infection decreases CD4+ T cell levels markedly increasing Mtb co-infections. An appropriate animal model for HIV/Mtb co-infection that can recapitulate the diversity of the immune response in humans during co-infection would facilitate basic and translational research in HIV/Mtb infections. Herein, we describe a novel humanized mouse model.

Methods

The irradiated NSG-SGM3 mice were transplanted with human CD34+ hematopoietic stem cells, and the humanization was monitored by staining various immune cell markers for flow cytometry. They were challenged with HIV and/or Mtb, and the CD4+ T cell depletion and HIV viral load were monitored over time. Before necropsy, the live mice were subjected to pulmonary function test and CT scan, and after sacrifice, the lung and spleen homogenates were used to determine Mtb load (CFU) and cytokine/chemokine levels by multiplex assay, and lung sections were analyzed for histopathology. The mouse sera were subjected to metabolomics analysis.

Results

Our humanized NSG-SGM3 mice were able to engraft human CD34+ stem cells, which then differentiated into a full-lineage of human immune cell subsets. After co-infection with HIV and Mtb, these mice showed decrease in CD4+ T cell counts overtime and elevated HIV load in the sera, similar to the infection pattern of humans. Additionally, Mtb caused infections in both lungs and spleen, and induced granulomatous lesions in the lungs. Distinct metabolomic profiles were also observed in the tissues from different mouse groups after co-infections.

Conclusion

The humanized NSG-SGM3 mice are able to recapitulate the pathogenic effects of HIV and Mtb infections and co-infection at the pathological, immunological and metabolism levels and are therefore a reproducible small animal model for studying HIV/Mtb co-infection.

A Novel Humanized Mouse Model for HIV and Tuberculosis Co-infection Studies

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), continues to be a major public health problem worldwide. The human immunodeficiency virus (HIV) is another equally important life-threatening pathogen. Further, co-infections with HIV and Mtb have severe effects in the host, with people infected with HIV being fifteen to twenty-one times more likely to develop active TB. The use of an appropriate animal model for HIV/Mtb co-infection that can recapitulate the diversity of the immune response in humans would be a useful tool for conducting basic and translational research in HIV/Mtb infections. The present study was focused on developing a humanized mouse model for investigations on HIV-Mtb co-infection. Using NSG-SGM3 mice that can engraft human stem cells, our studies showed that they were able to engraft human CD34+ stem cells which then differentiate into a full-lineage of human immune cell subsets. After co-infection with HIV and Mtb, these mice showed decrease in CD4+ T cell counts overtime and elevated HIV load in the sera, similar to the infection pattern of humans. Additionally, Mtb caused infections in both lungs and spleen, and induced the development of granulomatous lesions in the lungs, detected by CT scan and histopathology. Distinct metabolomic profiles were also observed in the tissues from different mouse groups after co-infections. Our results suggest that the humanized NSG-SGM3 mice are able to recapitulate the effects of HIV and Mtb infections and co-infection in the human host at pathological, immunological and metabolism levels, providing a dependable small animal model for studying HIV/Mtb co-infection.

Alterations in mast cell function and survival following in vitro infection with human immunodeficiency viruses-1 through CXCR4

HIV-1 infection leads to a disease that attacks the central regulatory mechanisms of the immune response. As mucosal tissue is one of the primary sites infected with HIV in vivo, we examined the effects of HIV exposure on human mast cells, important components of mucosal defense. Using the human mast cell line, HMC-1, which expresses CXCR4 but not CCR5 on the cell surface, we found that several HIV-1 X4 tropic lab (IIIB, RF) and primary isolates but not R5 (BAL, ADA) isolates productively infected these cells. Furthermore, stem cell factor-dependent mast cells derived from primary fetal liver or cord blood cultures were also productively infected with both X4 and R5 HIV-1 strains. Infection was blocked at the level of viral entry using monoclonal antibodies to CXCR4 and CD4. Treatment of HMC-1 with TNF-alpha and TGF-beta stimulated cell surface expression of CCR5 and up-regulated expression of both CCR5 and CXCR4 on primary mast cells, leading to increased susceptibility to both X4 and R5 viral isolates. HIV-1 infection also resulted in histamine release from these mast cells, most due in part to HIV-mediated cell death. These results demonstrate that X4 viruses can use CD4 and the CXCR4 receptor to infect mast cells, suggesting that mast cell-T cell interactions may contribute to HIV mediated immune dysfunction in the mucosa.

The immunoglobulin superantigen-binding site of HIV-1 gp120 activates human basophils

OBJECTIVE

To investigate the mechanism whereby HIV-1 envelope glycoprotein gp120 from four different isolates obtained in three different countries induces proinflammatory mediator release from normal human basophils.

METHODS

Histamine, cysteinyl leukotriene C4 (LTC4) and interleukin 4 (IL-4) release into the supernatant was measured in gp120-stimulated peripheral blood basophils from HIV-1 and HIV-2 negative subjects.

RESULTS

The HIV glycoprotein was a potent stimulus for release of these mediators in basophils purified from donors negative for HIV-1 and HIV-2. There was also a correlation (r = 0.58; P < 0.01) between the maximum IL-4 release from basophils induced by gp120 and by anti-IgE. Basophils from which IgE had been dissociated by brief exposure to lactic acid no longer released histamine in response to gp120 and anti-IgE. Anti-IgE specifically desensitized basophils to a subsequent challenge with anti-IgE and gp120. Human monoclonal IgM carrying the VH3 domain, but not that carrying the VH6 domain, inhibited gp120-induced secretion of histamine from basophils in a concentration-dependent manner. Synthetic peptides identical to regions distant from the N- and C-termini of gp120MN inhibited its activating capacity.

CONCLUSIONS

gp120 acts as a viral superantigen interacting with the VH3 domain of IgE to induce the release of preformed and de novo synthesized mediators from human cells carrying the Fc fragment Fc epsilonRI receptor.

HIV-1 gp120 induces IL-4 and IL-13 release from human Fc epsilon RI+ cells through interaction with the VH3 region of IgE

HIV-1 glycoprotein (gp) 120 from different clades is a potent stimulus for IL-4 and IL-13 release from basophils purified from healthy individuals seronegative for Abs to HIV-1 and HIV-2. IL-4 mRNA, constitutively present in basophils, was increased after stimulation by gp120 and was inhibited cyclosporin A and tacrolimus. IL-4 and IL-13 secretion from basophils activated by gp120 was not correlated. There was a correlation between the maximum gp120- and anti-IgE-induced IL-4 release from basophils. The average t1/2 gp120-induced IL-4 release was lower than for IL-13 release. Basophils from which IgE had been dissociated by brief exposure to lactic acid no longer released IL-4 in response to gp120 or to anti-IgE. The response to a mAb cross-linking the alpha-chain of high-affinity receptor for IgE (Fc epsilon RI) was unaffected by this treatment. Three human VH3+ monoclonal IgM inhibited gp120-induced secretion of IL-4 from basophils. In contrast, VH6+ monoclonal IgM did not inhibit the release of IL-4 induced by gp120. Synthetic peptides distant from the NH2 and COOH termini of gp120MN inhibited the activating property of gp120MN. These results indicate that gp120, which acts as a viral superantigen, interacts with the VH3 region of IgE to induce the release of IL-4 and IL-13 from human Fc epsilon RI+ cells.

Levels of gamma interferon and interleukin-4 are inversely related to the levels of their corresponding autoantibodies in patients with lower respiratory tract infection

To study the involvement of cytokines and their corresponding autoantibodies (Aabs) in inflammatory mechanisms in patients with lower respiratory tract infections, blood samples were taken from patients at the time of admission to the hospital and before treatment. Cell-released capturing enzyme-linked immunosorbent assay was used to measure the levels of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) produced spontaneously by peripheral mononuclear cells (PMNC). ELISA was used to measure Aabs to these cytokines in sera. The levels of both cytokines were inversely related to the levels of their corresponding Aabs. While a high level of IFN-gamma was observed together with a low level of anti-IFN-gamma Aab, decreased IL-4 levels were observed with increased levels of Aabs to IL-4. Immunoglobulins were purified, digested to obtain Fab fragments, and tested for specificity and cross-reactivity. The Aabs and their Fab fragments were tested in cytokine biological assays and showed neutralizing effects. Our data demonstrated increased levels of the proinflammatory cytokine IFN-gamma and decreased release of the anti-inflammatory cytokine IL-4 during early presentation of lower respiratory tract infection. The levels of these cytokines were inversely related to the levels of their corresponding Aabs that exhibited regulatory effects on the cytokine biological function in vitro.

Elevated IgE level in relationship to nutritional status and immune parameters in early human immunodeficiency virus-1 disease

Elevation of IgE has been associated with T-cell dysregulation and with the occurrence of opportunistic infections in patients with acquired immunodeficiency syndrome. The precise cause of IgE overproduction during the early stages of human immunodeficiency virus (HIV)-1 disease, however, has not been established. In light of reports demonstrating that IgE production may be affected by vitamin E levels in an animal model, we evaluated nutritional status in relationship to plasma IgE levels and immune parameters in 100 asymptomatic HIV-1-seropositive and 42 HIV-1-seronegative homosexual men. Approximately 18% of the HIV-1-seropositive population demonstrated biochemical evidence of plasma vitamin E deficiency (< 5 micrograms/ml). Subsequent analysis of available samples indicated a dramatic elevation of IgE levels (308 +/- 112 IU/ml) in vitamin E-deficient seropositive subjects (n = 9) as compared with age and CD4-matched HIV-1-seropositive persons with adequate vitamin E levels (n = 16, 118.1 +/- 41.1 IU/ml) and significantly lower levels (59.5 +/- 15.7 IU/ml) in HIV-1-seronegative men (n = 20, p = 0.01). This effect, which was independent of CD4 cell count, did not appear to be influenced by atopic or gastrointestinal parasitic disease. The low plasma vitamin E levels were related at least in part to dietary intake (r = 0.552, p = 0.01), suggesting that supplementation may be warranted in HIV-1-infected persons in whom vitamin E deficiency develops. Analysis of covariance revealed a strong relationship between IgE levels and CD8 cell counts (p < 0.006), and between IgE level and vitamin E deficiency (p < 0.039).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant CD4-IgE, a novel hybrid molecule, inducing basophils to respond to human immunodeficiency virus (HIV) and HIV-infected target cells

Basophils and mast cells, as the main effector cells in IgE-mediated type I hypersensitivity, are involved in the elimination of parasites and, according to recent findings, may also play an important role in the defense against bacterial and viral infections. Using a genetic engineering approach we wanted to redirect this potent IgE-mediated defense system against intruding human immune deficiency virus. We constructed a recombinant CD4-IgE molecule, consisting of the two N-terminal domains of CD4 and the CH2-4 domains of the IgE heavy chain, thus providing the IgE with specificity for the gp120 of human immunodeficiency virus (HIV). The binding properties of hybrid CD4-IgE to the high-affinity receptor for IgE (Fc epsilon RI) on basophils as well as to the low-affinity receptor (Fc epsilon RII or CD23) for IgE on lymphoid cells were found to be similar to those of native IgE. At the same time, the CD4 domains of the recombinant molecule retained the gp120 binding specificity with an affinity similar to that of the native CD4. By functional tests, we demonstrated that CD4-IgE armed basophils can be triggered by free HIV and by HIV-infected cells to release their mediators. We further show that HIV-triggered basophils lead to a decreased replication of HIV in susceptible T cells. We, therefore, conclude that the type I hypersensitivity effector cells can be engaged in the elimination of HIV-infected cells, at least in vitro. Because of the strong binding of the CD4-IgE construct to the Fc epsilon RI, we assume that CD4-IgE has a short t1/2 in serum, but may similarly to IgE exhibit prolonged resident time on basophils and mast cells, which are located close to mucosal surfaces or in the connective tissue. Thus CD4-IgE could play an important role in the elimination of HIV also in vivo.