Major histocompatibility complex (MHC) class I polymorphisms influence outcomes in a number of infectious diseases, cancers and inflammatory diseases. In human immunodeficiency virus (HIV) infections, among all genetic factors known to influence progression to acquired immunodeficiency syndrome (AIDS), the strongest associations link to human MHC class I genes. MHC class I molecules bind to peptide antigens and present these antigens to CD8 T cells. MHC class I molecules are also ligands for inhibitory receptors of NK cells Three sets of genes encode human MHC class I molecules which are the human leukocyte antigens (HLA) A, B and C. These genes are highly polymorphic, with the HLA-B genes being the most variable. It is generally assumed that HLA-disease associations link to the peptide binding characteristics of individual HLA class I molecules. However, it remains largely unknown whether and how differences in assembly characteristics or stabilities of HLA class I molecules influence immunological outcomes. A set of objectives of this application is to examine such influences. A central hypothesis is that the observed assembly and stability differences between HLA-B allotypes influence their cell surface expression, and their abilities to mediate CD8 T cell and NK cell responses.
In Aim 1, we show that dependence on the assembly factor tapasin is quite variable among HLA-B molecules. Tapasin-dependent assembly is highly prevalent within the HLA-Bw4 serotype, whereas many HLA-B molecules of HLA-Bw6 serotype are tapasin-independent for their assembly. HLA-Bw4 molecules but not HLA-Bw6 molecules are ligands for inhibitory receptors of natural killer (NK) cells, which are responsive to cell surface expression densities of MHC class I molecules. To further examine whether the HLA-Bw4/HLA- Bw6 segregation in tapasin dependence reflects altered cell surface expression of different allotypes, quantitative flow cytometry will be used to compare cell surface expression densities of HLA-B molecules in primary human CD4 T cells under basal conditions, and following infections with HIV-1.
In Aim 2, we show varying conformational stabilities of soluble peptide-deficient HLA-B molecules during their refolding, and variable levels of expression of HLA-B molecules on cells deficient in the transporter associated with antigen processing (TAP). Based on these findings, we will examine variable recognition of HLA-B molecules by endoplasmic reticulum (ER) quality control factors, and differing requirements for other assembly factors. The molecular basis for stability differences of the empty HLA-B proteins will be elucidated.
In Aim 3, we will examine whether the observed HLA-B assembly and stability differences influence the breadth and stability of peptide selection by HLA-B molecules. These analyses will be undertaken by comparing different HLA-B- restricted CD8 T cell responses against peptide antigens spanning the HIV proteome. Taken together, these studies are significant towards defining variations in immune functions of different HLA-B molecules, which are relevant towards vaccine design and infectious disease outcomes.
The studies described in this proposal are significant towards understanding how variations in human leukocyte antigens (HLA)-B influence their structure, cell surface expression and immune responses. These studies will ultimately be important towards vaccine design and immunotherapy that is individualized and based on the HLA genotype.
|Rizvi, Syed Monem; Salam, Nasir; Geng, Jie et al. (2014) Distinct assembly profiles of HLA-B molecules. J Immunol 192:4967-76|
|Rizvi, Syed Monem; Del Cid, Natasha; Lybarger, Lonnie et al. (2011) Distinct functions for the glycans of tapasin and heavy chains in the assembly of MHC class I molecules. J Immunol 186:2309-20|
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|Rizvi, Syed Monem; Raghavan, Malini (2006) Direct peptide-regulatable interactions between MHC class I molecules and tapasin. Proc Natl Acad Sci U S A 103:18220-5|
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|Thammavongsa, Vilasack; Raghuraman, Gayatri; Filzen, Tracy M et al. (2006) HLA-B44 polymorphisms at position 116 of the heavy chain influence TAP complex binding via an effect on peptide occupancy. J Immunol 177:3150-61|
|Thammavongsa, Vilasack; Mancino, Laura; Raghavan, Malini (2005) Polypeptide substrate recognition by calnexin requires specific conformations of the calnexin protein. J Biol Chem 280:33497-505|
|Yang, Tianyu; Lapinski, Philip E; Zhao, Haotian et al. (2005) A rare transporter associated with antigen processing polymorphism overpresented in HLAlow colon cancer reveals the functional significance of the signature domain in antigen processing. Clin Cancer Res 11:3614-23|
|Lapinski, Philip Edward; Raghuraman, Gayatri; Raghavan, Malini (2003) Nucleotide interactions with membrane-bound transporter associated with antigen processing proteins. J Biol Chem 278:8229-37|
|Raghuraman, Gayatri; Lapinski, Philip Edward; Raghavan, Malini (2002) Tapasin interacts with the membrane-spanning domains of both TAP subunits and enhances the structural stability of TAP1 x TAP2 Complexes. J Biol Chem 277:41786-94|
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