Research Summary

Our research program is focused on biology and function of MHC class I proteins in antigen presentation in tissue transplantation and during infection. This program has four areas of interest discussed below.

Mechanisms of release of soluble MHC class I. In mammals, MHC class I molecules are expressed on the surface of nearly all nucleated cells as integral membrane proteins and also as soluble proteins in many body fluids. The majority of soluble MHC class I are released from cell surface via proteolytic cleavage mediated by A Disintegrin And Metalloprotease (ADAM) family member such as ADAM17. The metalloproteinase pathway of MHC class I release produces two types of proteins: soluble class I heavy chains without peptides and soluble MHC class I complexes with bound high-affinity peptides. Pro-inflammatory cytokines (IFNg and TNFa) stimulate constitutive release of soluble MHC class I proteins mediated by ADAM17 in various cell types. However, in professional antigen-presenting cells (macrophages and dendritic cells), the release of soluble MHC class I can also be induced by tissue-specific cytokine GM-CSF. The latter is mediated by another yet unidentified metalloproteinase. Interactions of ADAM17 with its substrate, MHC class I, requires translocation of cell surface proteins into intracellular compartments such as acidic endosomes via clathrin-coated pits.

Soluble MHC class I in alloantigen presentation. Accumulated evidence obtained, in part, in transplantation studies suggests an important role for soluble MHC class I in antigen presentation. Soluble MHC class I proteins can modulate host immune responses by entering the cross-presentation pathways and by interacting with T and B cell receptors. Additionally, soluble MHC class I can enter the indirect pathway of allorecognition, in which host T cells recognize foreign MHC class I peptides presented in the context of self MHC class II. Presentation of soluble MHC class I via the indirect allorecognition pathway can modulate activity of alloreactive CD4+ and CD8+ T cells and explain its involvement in the pathogenesis of allograft rejection. Therefore, understanding this process at the molecular level is important for transplantation therapy.

Th1 immunity in tuberculosis. Recent data suggest that Th1-type CTL responses against novel M. tuberculosis targets identified in our lab, alanine dehydrogenase (Rv2780) and glutamine synthetase (Rv2220), can be detected only in non-vaccinated, tuberculin skin test-positive asymptomatic individuals but not in active tuberculosis patients, while responses to superoxide dismutase (Rv3846) were present in both groups. This finding supports the notion that in humans the profile of antigen-specific responses associated with active disease differs from that observed during latent infection. Complex interactions between the bacterial pathogen and host immune system underline this dynamics. For example, selection of initial CTL targets and possible 're-targeting' in the course of infection may be related to certain profound changes in the program of mycobacterial gene expression during infection. Additionally, CTL responses are likely to be affected by the antigen load and presentation pathways. It is possible that in latent infections, when the pathogen antigen levels are quite low, soluble MHC class I can serve as enrichment mechanism for the pools of specific high-affinity peptides providing for CTL stimulation and/or memory maintenance via cross-presentation pathways. The latter cross-presentation mechanisms are the focus of this laboratory and may be evaluated in the mouse model of mycobacterial infection utilizing mice transgenic for human MHC class I.

Endothelial and antigen-presenting cell interactions in CMV infection. CMV infection drastically reduces the levels of MHC class I expression in infected endothelial cells (EC), impairs antigen presentation by dendritic cells and further modulates host immune responses by multiple but ill-defined mechanisms. Presently, we are focusing on the mechanisms altering expression of soluble MHC class I in CMV-infected cells. Current experiments with clinical isolates of human CMV suggest that transmission of infective particles from EC to macrophages requires cell-cell contact and has a profound effect on release of soluble MHC class I from both types of infected cells. The metalloproteinase pathway releasing soluble MHC class I proteins with high-affinity peptides is completely blocked by CMV infection. Instead, CMV induces the release of soluble class I-like and viral proteins (MICA, UL18) mediated by yet unidentified cellular protease. The signaling pathways activated by CMV in EC and antigen-presenting cells and the cellular receptors for these soluble proteins are being investigated.




Recent Articles


Mizrahi, S., Markel, G., Porgador, A., Bushkin, Y. and O. Mandelboim. (2007).
CD100 on NK cells enhance IFNg secretion and killing of target cells expressing CD72.
PLoS ONE. 2007 Sep 5;2(9):e818
PMID: 17786190

Dong, Y., Demaria, S., Sun, X., Santori, F.R., Jesdale, B,M., DeGroot, A., Rom, W.N. and Y Bushkin. (2004).
HLA-A2-restricted CD8+ cytotoxic T-cell responses to novel Mycobacterium tuberculosis targets superoxide dismutase, alanine dehydrogenase and glutamine sythetase.
Infect Immun. 2004 Apr;72(4):2412-5
PMID: 15039371
Abstract  |  Full Article

Dong Y, Lieskovska J, Kedrin D, Porcelli S, Mandelboim O, Bushkin Y. (2003).
Soluble nonclassical HLA generated by the metalloproteinase pathway.
Hum Immunol. 2003 Aug;64(8):802-10.
PMID: 12878359
Abstract  |  Full Article

Haynes L, Bushkin Y, Love R, Burlingham W. (2002).
Interferon-gamma drives the metalloproteinase-dependent cleavage of HLA class I soluble from primary human bronchial epithelial cells.
Hum Immunol 2002 Oct;63(10):893-901
PMID: 12368042
Abstract  |  Full Article

Mandelboim O, Lieberman N, Lev M, Paul L, Arnon TI, Bushkin Y, Davis DM, Strominger JL, Yewdell JW, Porgador A. (2001).
Recognition of haemagglutinins on virus-infected cells by NKp46 activates lysis by human NK cells.
Nature 2001 Feb 22;409(6823):1055-60
PMID: 11234016
Abstract  |  Full Article


PubMed Lisitings>




C.V.

Education
Latvian State University, Riga, Latvia, and Institute of Cytology, St. Petersburg, Russia, M.S., 1971 (Cytogenetics); Weizmann Institute of Science, Rehovot, Israel, Ph.D., 1978 (Cell Biol. and Genetics); Sloan-Kettering Institute for Cancer Research, New York, NY, Post Doc., 1977-1981 (Immunogenetics).

Positions
Sloan-Kettering Institute for Cancer Research, New York, NY, Research Associate, 1981-1986; New York University Medical Center, Research Associate Professor, New York, NY, Department of Pathology, 1989-present; PHRI, Associate, Department of Retroviral Biology, 1986-1988, Assistant Member, Head of the Laboratory of Molecular Immunology, 1988-1996, Associate Member, Head of the Laboratory of Molecular Immunology, 1996-present, University of Medicine and Dentistry, New Jersey Medical School, Adjunct Professor (Dept. of Medicine) 2006-present.