HIV-1 Tat dysregulation of lipopolysaccharide-induced cytokine responses: microbial interactions in HIV infection.
OBJECTIVE
To examine whether the HIV-1 Tat protein impairs the lipopolysaccharide (LPS)-induced cytokine responses.


METHODS
Concurrent infections with pathogens including bacteria and viruses are common in AIDS patients. However, cytokine and interferon responses during infection with or translocation from the gut of these pathogens in HIV-infected patients are not well studied. As HIV-1 Tat contributes partly to the HIV-induced immune dysregulation, we investigated whether the protein may play a role in perturbing the LPS-induced cytokine responses.


METHODS
Expression levels of cytokines in human primary blood monocytes/macrophages were determined by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Expression level of the cell surface Toll-like receptor 4 was examined by flow cytometry. Activations of signaling molecules were assayed by western blot and immunofluorescence.


RESULTS
We demonstrated that HIV-1 Tat downregulated the LPS-induction of IFN-beta and concomitantly upregulated IL-6 expression in primary blood monocytes/macrophages, whereas the viral protein had no significant effects on TNF-alpha expression. To delineate the underlying mechanism, we showed that Tat inhibited the LPS-activation of ERK1/2 but not the p38 mitogen-activated protein kinases. The viral protein suppressed the LPS-induced activation of NFkappaB p65 via its induction of IkappaBalpha expression, which resulted in retention of NFkappaB p65 in the cytosol.


CONCLUSIONS
These findings suggest that Tat may play a role in modulating the immune responses triggered by other coinfecting pathogens and thus providing a permissive environment for both HIV and other opportunistic microbes.
Yim
Howard C H
HC
Cytokine Biology Group, Department of Paediatrics and Adolescent Medicine, China bBio-Screening Unit, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
Li
James C B
JC
Lau
Jonathan S H
JS
Lau
Allan S Y
AS
D017088:AIDS-Related Opportunistic Infections / Q000276:immunology; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics; D015658:HIV Infections / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance; D016899:Interferon-beta / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D015850:Interleukin-6 / Q000096:biosynthesis; D018950:Lipopolysaccharide Receptors / Q000097:blood; D008070:Lipopolysaccharides / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology; D008264:Macrophages / Q000276:immunology; D009000:Monocytes / Q000276:immunology; D016328:NF-kappa B / Q000096:biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000276:immunology*
D016207:Cytokines; D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D016328:NF-kappa B; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D054322:tat Gene Products, Human Immunodeficiency Virus; D016899:Interferon-beta