A critical role for conserved residues in the cleft of HLA-A2 in presentation of a nonapeptide to T cells.

The peptide binding cleft of the class I human histocompatibility antigen, HLA-A2, contains conserved amino acid residues clustered in the two ends of the cleft in pockets A and F as well as polymorphic residues. The function of two conserved tyrosines in the A pocket was investigated by mutating them to phenylalanines and of a conserved tyrosine and threonine in the F pocket by mutating them to phenylalanine and valine, respectively. Presentation of influenza virus peptides and of intact virus to cytolytic T lymphocytes (CTLs) was then examined. The magnitude of the reduction seen by the mutation of the two tyrosines in the A pocket suggests that hydrogen bonds involving them have a critical function in the binding of the NH2-terminal NH3+ of the peptide nonamer and possibly of all bound peptide nonamers. In contrast, the mutations in the F pocket had no effect on CTL recognition.

Identification of the nonamer peptide from influenza A matrix protein and the role of pockets of HLA-A2 in its recognition by cytotoxic T lymphocytes.

Influenza matrix peptide 58-66 is shown to be the optimal nonamer for binding to HLA-A2 and presentation to cytotoxic T lymphocytes (CTL). If titered out to 2 x 10(-10) - 4 x 10(-10) M in CTL-mediated lysis assays and to 3 x 10(-9) M in an HLA-A2 assembly-stabilization assay in cell lysates. The peptide was shown to make probable contacts with its carboxy terminus close to residue 116 in the floor of the cleft of HLA-A2, close to the F pocket. The side chain of the amino-terminal amino acid was unimportant, but its free amino and carbonyl groups in the A pocket appeared important in optimizing peptide presentation. The B pocket probably accommodates the side chain of residue 2 (isoleucine) and was shown to be critical in peptide presentation.

Positioning of a peptide in the cleft of HLA-A2 by complementing amino acid changes.

Several mutant HLA-A2 molecules have been constructed and expressed in the mutant human B-cell line C1R, which lacks HLA-A and HLA-B antigens, and examined for presentation of a previously defined peptide epitope derived from the influenza matrix protein to appropriate human cytotoxic T-lymphocyte lines. When leucine residue 66 in this matrix peptide containing residues 57-68 (matrix peptide 57-68) was replaced by arginine, the resulting matrix peptide 57-68 R66 was not presented to HLA-A2, but the mutation Y116D (tyrosine to aspartic acid at residue 116) in the floor of the peptide binding cleft near its right end dramatically restored peptide presentation. A similar result was obtained by substitution of ornithine for leucine at residue 66. These data provide strong support for a model in which the peptide is orientated with its amino terminus at the left end of the cleft of HLA-A2 and its carboxyl terminus at the right.

Transcriptional control of MHC class II gene expression during differentiation from B cells to plasma cells.

In this study we investigated the molecular mechanisms responsible for the extinction of the constitutive MHC class II gene expression of human B cells on somatic cell hybridization with murine plasmocytoma cells. We found that this event is due to trans-acting suppressor functions of mouse origin pre-existing in the plasmocytoma cells and acting at transcriptional level. Transcription of the entire family of human class II genes is suppressed, including genes as DO beta for which a distinct regulation of expression in B cells had been previously demonstrated. Suppression appears specific for class II genes because in the hybrids expression of MHC class I genes of mouse is unaffected and of human only partially reduced. Interestingly, also murine invariant chain gene is expressed in both parental plasmocytoma and hybrid cells although at reduced amounts as compared to a murine class II positive B cell line. The class II negative phenotype of hybrid cells and parental plasmocytoma cells is highly stable and unaffected by treatment with protein synthesis inhibitors, suggesting that the transcriptional suppressor function is not mediated by rapid, labile turning-over proteins. Possible mechanisms responsible for transcriptional regulation of MHC class II gene expression during terminal differentiation of B cells to plasma cells are discussed.

Active suppression of major histocompatibility complex class II gene expression during differentiation from B cells to plasma cells.

Constitutive expression of major histocompatibility complex class II genes is acquired very early in B-cell ontogeny and is maintained up to the B-cell blast stage. Terminal differentiation in plasma cells is, however, accompanied by a loss of class II gene expression. In B cells this gene system is under the control of several loci encoding transacting factors with activator function, one of which, the aIr-1 gene product, operates across species barriers. In this report human class II gene expression is shown to be extinguished in somatic cell hybrids between the human class II-positive B-cell line Raji and the mouse class II-negative plasmacytoma cell line P3-U1. Since all murine chromosomes are retained in these hybrids and no preferential segregation of a specific human chromosome is observed, the results are compatible with the presence of suppressor factors of mouse origin, operating across species barriers and inhibiting class II gene expression. Suppression seems to act at the level of transcription or accumulation of class II-specific mRNA, since no human, and very few murine, class II transcripts are detectable in the hybrids.

Immunochemical characterization of the human blood cell membrane glycoprotein recognized by the monoclonal antibody 12E7.

The 12E7 murine monoclonal antibody recognizes a protease-sensitive component of human red cells, platelets and lymphocytes which could not be detected on granulocytes. Scatchard analyses indicated that the 125I-labelled antibody binds to 1000, 4000 and 27,000 antigen sites on each red cell, platelet and lymphocyte respectively, with a binding constant ranging from 4 x 10(7) to 9 x 10(7) M-1. The membrane components recognized by the monoclonal antibody were characterized by immunostaining on nitrocellulose sheets. A 28 kDa sialoglycoprotein was visualized following electrophoretic transfer of the red cell and lymphocyte membrane proteins separated by SDS/polyacrylamide-gel electrophoresis. Another component of 25 kDa was also clearly identified in the lymphocyte and platelet lysates, but was barely detectable in the red cell membrane preparations. Enzyme treatment of intact platelets, as well as analysis of the membrane and cytosolic preparations from these cells, have shown that the 25 kDa component was of cytoplasmic origin. The mobility of the 28 kDa membrane component is decreased following neuraminidase treatment of intact blood cells, but these cells still react normally with the monoclonal antibody, indicating that sialic acids are not required for binding. The 28 kDa component is present on red cell membranes prepared from S-s-U-, En(a-) and Gerbich(-) individuals, demonstrating that it is a new sialoglycoprotein not derived from glycophorins A, B, C or D. The 28 kDa component was totally solubilized with 0.1% Triton X-100 from red cell membranes and behaves like the other red cell membrane sialoglycoproteins since it was extracted in the aqueous phase following chloroform/methanol/water or butanol/water partitionings. The 28 kDa component could be partially purified by h.p.l.c. gel permeation chromatography and preparative SDS/polyacrylamide-gel electrophoresis. The material finally obtained strongly inhibits the 12E7 monoclonal as well as human anti-Xga antibodies, suggesting either that the 28 kDa glycoprotein carries both antigens or that the 12E7 and Xga-active molecules copurified.

Glycophorins B and C from human erythrocyte membranes. Purification and sequence analysis.

We have developed methods for the preparative purification of two sialoglycoproteins (glycophorins B and C) from human erythrocyte membranes by high-performance ion exchange and gel permeation chromatography in the presence of Triton X-100. Glycophorin B was obtained without any detectable contaminants, and glycophorin C exhibited a purity of about 90-95%. The amino acid sequence of the intramembranous domain (residues 36-71) of glycophorin B was determined and found to be similar to that of the hydrophobic region of the major sialoglycoprotein (glycophorin A). The amino acid sequence of the hydrophobic domain (residues 49-88) of glycophorin C, that was also determined, agreed completely with the structure recently deduced from cDNA sequencing.

Evidence of a preferential inactivation of the paternally derived X chromosome in a 46,XX true hermaphrodite.

The pattern of inheritance of several X polymorphic markers is studied in the pedigree of a 46,XX true hermaphrodite. The results of the Xga, 12E7, and G6PD segregation analysis favour the hypothesis of a preferential inactivation of the paternally derived X chromosome.

[Genetic, biochemical and functional study of the H-Y antigen in man]. / Etude génétique, biochimique et fonctionnelle de l'antigène H-Y chez l'homme.

H-Y antigen, first described as a male minor transplantation antigen, is unvarying associated with testicular differentiation, more than the presence of Y chromosome. The weak reactivity of anti H-Y serum needs quantitative and very sensitive tests to detect presence or absence of H-Y. This antigen may act as an hormone, to induce testicular differentiation of target cells, bearing a specific receptor at their surface. The relationship between an H-Y molecule immunologically defined by its antigenicity and H-Y factor defined by its function to induce testicular organogenesis must be determined.