Ed Barker, PhD

Degrees and Certifications:
BS and PhD

Rank and Title:
Assistant Professor

Department:
Immunology/Microbiology

Endowed Professorship:

Office Location:
1735 W. Harrison
620 Cohn Bldg
Chicago, IL 60612

Laboratory Location:
1735 W. Harrison
653 Cohn Bldg
Chicago, IL 60612

Phone:
312-942-3136

Fax:
312-942-2808

E-mail:
Edward_Barker@rush.edu

Education:
Graduate: University of Illinois at Chicago, Chicago, IL 1984-1990
Postdoctoral Fellowship: Research Institute of Scripps Clinic, La Jolla, CA 1990-1992
Postdoctoral Fellowship: University of California, San Francisco, CA 1992-1996

Laboratory Techniques:
Cytokine Assessment
Flow Cytometry
Gene Transfection
Imaging Technology
PCR
Real-time PCR
si RNA
Tissue Culture (Primary, Cell Line)
Ultra centrifugation techniques
Western Northern Southern Blotting

Hyperlinks:

Documents:

Faculty/Staff Description:
HIV downregulates the classical MHC-I molecules, HLA-A and HLA-B, on the infected cell surface as a means to avoid destruction by HIV antigen-specific CD8+ cytotoxic T-lymphocytes (CTL). However, by reducing HLA-A and -B, the infected cells may become vulnerable to killing by natural killer (NK) cells that are negatively controlled by the presence of these MHC-I on the target cell. Despite HLA-A and -B down-modulation by HIV-1 Nef, HLA-C and -E remain on the infected cell surface and prevent NK cell killing by interacting with specific inhibitory (INH) receptors on NK. Although HLA-C and -E effectively inhibit NK responses when engaging their counterpart inhibitory receptors, only a subset of NK expresses the appropriate INH receptors for HLA-C and/or -E. Thus, a significant proportion of NK cells should be able to kill HIV-infected targets. Yet, we find that infected lymphocytes are largely refractory to killing by NK lacking INH receptors to HLA-C and -E. Therefore, we proposed that additional, unsuspected, factors must contribute to the protection of infected T-lymphocytes from recognition as targets by NK cells. We have recently identified another MHC class I molecule, HLA-G, as being a potent suppressor of NK cell activity against HIV-infected cells. HLA-G is normally expressed on trophoblasts and is thought to prevent maternal NK cells from attacking fetal tissue. HLA-G has never been reported to be expressed on the surface of CD4+ T-lymphocytes. Remarkably, we demonstrate that HIV infection induces surface expression of HLA-G on CD4+ T-cells. Moreover, we have observed that silencing HLA-G, via RNAi, leads to NK cell killing of otherwise resistant HIV-1 infected cells. The central hypothesis of this study is that HIV prevents NK from killing infected cells and controlling viral replication by inducing the expression of HLA-G. This constitutes another mechanism, in addition to Nef's downregulation of HLA-A and B, by which HIV renders infected cells resistant to immune surveillance.

Unlike cytotoxic T-lymphocytes, natural killer cells (NK) are not activated towards granule release by specific peptide antigens in the context of MHC Class I but rather by the presence of ligands on target cells recognized by germline encoded receptors, such as NKG2D and the natural cytoxicity receptors (NKp30, NKp44, and NKp46). However very little is know about what triggers NK cells to kill the infected cells. We sought to determine the presence or absence on HIV-1 infected cells of ligands to NK activating receptors (e.g. NCR's, NKG2D), and the NK activating coreceptors (e.g., NTB-A and 2B4), as well as their role in destruction of infected cells by NK. Three of the ligands for NKG2D; ULBP-1, -2, and -3, are expressed on CD4+ T-cells infected with X4 and R5 HIV strains, and are absent on mock-infected cells. These molecules trigger NK destruction of HIV-infected cells as demonstrated by the ability to significantly decrease killing of the infected cells when the interaction between NKG2D and its ligands is blocked. The identity of the ligands for the three NCRs are presently unknown, however, staining of HIV-1 infected cells with recombinant NCR-Fc fusion proteins has revealed that NKp44 ligand is present on the cell surface of HIV-1 p24 antigen negative cells of HIV-1 infected cells but not the p24 antigen positive cells. None of the NKp30 and NKp46 ligand(s) have been shown to be significantly upregulated on the surface of infected cells. NTB-A and 2B4 are NK cell coreceptors, as they have been shown to trigger NK target cell killing upon recognition of their ligands (NTB-A and CD48, respectively) when NKG2D or NCRs are also engaged by their ligands. We have shown that that the killing of HIV-1 infected cells by NK is NTB-A and 2B4 dependent, however, both CD48 and NTB-A are significantly downregulated from the surface of HIV-1 infected cells. The central hypothesis of this study is that HIV prevents NK from killing infected cells and controlling viral replication not only by altering MHC class I molecule expression but also by selectively modulating key activating ligands. This later observation may explain why HIV-infected cells lacking inhibitory receptors to HLA-C and -E do not kill HIV-infected cells to their fullest potential. In summary, HIV has the ability to modulate NK activating receptors that affects the capacity of NK to destroy infected cells.

Selected Publications: