Detection of fungal carbohydrate antigens by high-performance immunoaffinity chromatography using a protein A column with covalently linked immunoglobulin G

Exploration of peptides bound to MHC class I molecules in melanoma

Advancements in high-resolution HPLC and mass spectrometry have reinvigorated the application of this technology to identify peptides eluted from immunopurified MHC class I molecules. Three melanoma cell lines were assessed using w6/32 isolation, peptide elution and HPLC purification; peptides were identified by mass spectrometry. A total of 13,829 peptides were identified; 83-87% of these were 8-11 mers. Only approximately 15% have been described before. Subcellular locations of the source proteins showed even sampling; mRNA expression and total protein length were predictive of the number of peptides detected from a single protein. HLA-type binding prediction for 10,078 9/10 mer peptides assigned 88-95% to a patient-specific HLA subtype, revealing a disparity in strength of predicted binding. HLA-B*27-specific isolation successfully identified some peptides not found using w6/32. Sixty peptides were selected for immune screening, based on source protein and predicted HLA binding; no new peptides recognized by antimelanoma T cells were discovered. Additionally, mass spectrometry was unable to identify several epitopes targeted ex vivo by one patient's T cells.

Quantitative and qualitative influences of tapasin on the class I peptide repertoire

Tapasin is critical for efficient loading and surface expression of most HLA class I molecules. The high level surface expression of HLA-B*2705 on tapasin-deficient 721.220 cells allowed the influence of this chaperone on peptide repertoire to be examined. Comparison of peptides bound to HLA-B*2705 expressed on tapasin-deficient and -proficient cells by mass spectrometry revealed an overall reduction in the recovery of B*2705-bound peptides isolated from tapasin-deficient cells despite similar yields of B27 heavy chain and beta(2)-microglobulin. This indicated that a proportion of suboptimal ligands were associated with B27, and they were lost during the purification process. Notwithstanding this failure to recover these suboptimal peptides, there was substantial overlap in the repertoire and biochemical properties of peptides recovered from B27 complexes derived from tapasin-positive and -negative cells. Although many peptides were preferentially or uniquely isolated from B*2705 in tapasin-positive cells, a number of species were preferentially recovered in the absence of tapasin, and some of these peptide ligands have been sequenced. In general, these ligands did not exhibit exceptional binding affinity, and we invoke an argument based on lumenal availability and affinity to explain their tapasin independence. The differential display of peptides in tapasin-negative and -positive cells was also apparent in the reactivity of peptide-sensitive alloreactive CTL raised against tapasin-positive and -negative targets, demonstrating the functional relevance of the biochemical observation of changes in peptide repertoire in the tapasin-deficient APC. Overall, the data reveal that tapasin quantitatively and qualitatively influences ligand selection by class I molecules.

Survey of recent advances in analytical applications of immunoaffinity chromatography

Methods that use immunoaffinity chromatography (IAC) for sample preparation or detection are becoming increasingly popular as tools in the analysis of biological and nonbiological compounds. This paper presents an overview of immunoaffinity chromatography and examines some recent developments of this technique in analytical applications. The emphasis is placed on HPLC-based IAC methods or those that combine IAC with other instrumental techniques; however, novel approaches that employ low-performance IAC columns for chemical quantitation are also considered. Particular applications that are examined include (1) the use of IAC in the direct detection of analytes, (2) the extraction of samples by IAC prior to on- or off-line detection by other methods, (3) the use of IAC in chromatographic-based immunoassays, and (4) the development of postcolumn reactors based on IAC for the detection of analytes as they elute from other types of chromatographic columns. The advantages and limitations for each approach are considered. In addition, a summary is provided of reports in the literature that have used IAC for these various formats.

Molecular orientation distributions in protein films: III. Yeast cytochrome c immobilized on pyridyl disulfide-capped phospholipid bilayers

Molecular orientation in a hydrated monolayer film of yeast cytochrome c, immobilized via disulfide bonding between Cys-102 and a pyridyl disulfide-capped phospholipid bilayer deposited from an air-water interface onto glass substrates, was investigated. The orientation distribution of the heme groups in the protein film was determined using a combination of absorption linear dichroism, measured in a planarintegrated optical waveguide-attenuated total reflection geometry- and fluorescence anisotropy, measured in a total internal reflection geometry. A gaussian model for the orientation distribution was used to recover the mean heme tilt angle and angular distribution about the mean, which were 40 and 11 degrees, respectively. Additional experiments showed that a large fraction of the cytochrome c was disulfide bonded to the bilayer, which correlates with the high degree of macroscopic order in the protein film. However, a subpopulation of yeast cytochrome c molecules in the film (approximately 30% of the total) appeared to be nonspecifically adsorbed. The orientation distribution of this subpopulation was found to be much broader than the specifically bound fraction.