Search PubMed⌕ Search

Biomedical subjects

P Parham

Publications and source records attributed to P Parham.

At least 289 records · Page 16Linked to original sources
PubMed1988

Nature of polymorphism in HLA-A, -B, and -C molecules.

Diversity in 39 HLA-A, -B, and -C molecules is derived from 20 amino acid positions of high variability and 71 positions of low variability. Variation in the structurally homologous alpha 1 and alpha 2 domains is distinct and may correlate with partial segregation of peptide and T-cell receptor binding functions. Comparison of 15 HLA-A with 20 HLA-B molecules reveals considerable locus-specific character, due primarily to differences at polymorphic residues. The results indicate that genetic exchange between alleles of the same locus has been a more important mechanism in the generation of HLA-A, -B, and -C diversity than genetic exchange events between alleles of different loci.

Amino Acid Sequence↗
PubMed1987

The ability of cytotoxic T cells to recognize HLA-A2.1 or HLA-B7 antigens expressed on murine cells correlates with their epitope specificity.

Two groups of human and murine cytotoxic T lymphocyte (CTL) clones specific for human leukocyte antigen (HLA)-A2 or -B7 can be distinguished based on their ability to kill murine transfectants expressing these molecules. The clones which do not recognize murine transfectants exhibited greatly reduced conjugate formation with these cells, indicating that the inability to lyse these cells occurs in recognition and binding. No systematic differences in inhibitory titer between the two types of CTL clones were seen with anti-CD8 (Lyt-2), anti-LFA-1, or monoclonal antibodies against HLA class I molecules. However, blocking with anti-HLA class I monoclonal antibodies suggested that different CTL clones recognized spatially separate epitopes on HLA-A2 and -B7. In addition, a correlation between the inability to recognize murine transfectants and fine specificity was seen. Eight of nine clones which did not lyse murine transfectants also failed to recognize human cells expressing HLA-A2.2 or -A2.3. In contrast only 5 of 12 clones which lysed transfectants failed to recognize the variant molecules. Analogous data were obtained with human CTL clones raised against HLA-A2.1. These findings suggest that CTL clones that do not lyse murine cells expressing appropriate antigens recognize epitopes that have been altered or lost as a consequence of expression on the murine cell surface. It is suggested that the loss of HLA-associated epitopes on the murine cell surface may be due to differences between mouse and human cells in the processing or presentation of class I-associated peptides.

Animals↗
PubMed1987

Multiple genetic mechanisms have contributed to the generation of the HLA-A2/A28 family of class I MHC molecules.

The genetic events that produce diversity in class I MHC genes and proteins has been investigated by using a family of closely related HLA-A alleles. Five genes coding for HLA-A2.2Y, HLA-A2.3, and HLA-Aw68.2 have been isolated. Exon sequences are compared with the known sequences for HLA-A2.1, HLA-A2.2F, HLA-A2.4, HLA-Aw68.1, and HLA-Aw69. Pairwise comparison of the eight unique sequences shows that point mutation, reciprocal recombination, and gene conversion have all contributed significantly to the diversification of this family of alleles. These results are compared with those of other studies that have emphasized the role of gene conversion. A predominance of coding substitutions in the alpha 1 and alpha 2 domains is found, consistent with positive selection for polymorphism being a major factor in the fixation of these alleles. In the three cases examined, genes for phenotypically identical proteins gave identical nucleotide sequences, indicating that most, if not all, of the class I polymorphism is detectable by immunological methods. The apparent stability of the sequences suggests that the events generating some of the alleles occurred before the origin of modern Homo sapiens.

Alleles↗
PubMed1987

In vitro mutagenesis at a single residue introduces B and T cell epitopes into a class I HLA molecule.

We have studied the interaction of HLA class I antigens with alloreactive cytotoxic T lymphocytes and monoclonal antibodies using site-directed mutagenesis and expression of an HLA-Aw68.1 gene. Two mutants containing distinct substitutions at polymorphic residues near the NH2-terminal end of the alpha 2 domain were made. One mutant with substitutions at positions 95 and 97 corresponding to residues found in HLA-A2.1 showed no alterations in binding of HLA-Aw68- or HLA-A2-specific monoclonal antibodies, but was reactive with some HLA-A2-specific CTL clones. A second mutant, in which glycine at position 107 was replaced with tryptophan found at that position in HLA-A2.1, was recognized by HLA-A2-specific CTL clones and HLA-A2, Aw69-specific monoclonal antibodies. Thus, substitution of a single amino acid residue at position 107 of the HLA-Aw68.1 molecule generates an allospecific determinant shared with HLA-A2.1 and recognized by both B and T lymphocytes.

Amino Acid Sequence↗
PubMed1987

Identification and characterization of two novel lymphocyte function-associated antigens, L24 and L25.

We describe the function and cell distribution of two novel cell surface antigens, L24 and L25. These antigens are broadly distributed on human lymphocytes. Monoclonal antibodies specific for these molecules block lysis by Class I- and II-specific cytotoxic T lymphocytes, but do not affect any other T cell functions tested. Anti-L24 antibody immunoprecipitates a molecule composed of two disulfide-linked monomers of 140 kd each. Anti-L25 antibody immunoprecipitates three proteins of 150, 85, and 75 kd. The study of these and other function associated molecules may provide insight into mechanisms of cytotoxic T lymphocyte recognition and/or function.

Antibodies, Monoclonal↗
PubMed1987

A transposable epitope of HLA-B7, B40 molecules.

The monoclonal antibody MB40.2 defines a novel subtype of HLA-B40 that is expressed by the Sweig cell line. This molecule, called HLA-B40, lacks an antigenic determinant that is common to HLA-B7 and the HLA-Bw60 subtype of HLA-B40. Genes encoding HLA-B40 and HLA-Bw60 have now been isolated and the amino acid sequences of these proteins compared with other HLA-B locus molecules. These results show that HLA-B40 is a unique protein which differs from HLA-Bw60 by eight amino acid substitutions. Comparison of the sequences for HLA-B40, -Bw60, and -B7 localizes the MB40.2 epitope to a cluster of three substitutions at positions 177, 178, and 180 at the end of the alpha 2 domain. Gene conversion or reciprocal recombination are postulated to have transferred this cluster of substitutions, and their associated epitope, during the evolution of HLA-B locus genes. The epitope may consist of an alpha helical segment which is exclusively found on MB40.2-positive molecules.

Amino Acid Sequence↗
PubMed1986

The primary structure of HLA-A32 suggests a region involved in formation of the Bw4/Bw6 epitopes.

All HLA-B locus molecules have either the Bw4 or Bw6 epitopes. In addition, the Bw4 epitope is found on HLA-Aw23, Aw24, and A32, and Bw6 is also found on HLA-Cw3. The structural basis for these determinants and the evolution of their distribution among products of the HLA-B locus has been a long standing puzzle. To identify residues that may be involved in these determinants, we have cloned a gene for A32 and sequenced the protein encoding exons. Comparison of the predicted protein sequence with other HLA-A,B,C sequences identified residues 79 through 83 of the alpha 1 domain as having a pattern of polymorphic substitution that correlates with the presence and absence of the Bw4 and Bw6 epitopes.

Amino Acid Sequence↗
PubMed1986

Amino acid residues 56 to 69 of HLA-A2 specify an antigenic determinant shared by HLA-A2 and HLA-B17.

The mouse monoclonal antibody MA2.1 was previously used to define an epitope shared by native HLA-A2 and HLA-B17 molecules and amino acid sequence comparison of nine HLA-A,B,C molecules identified residues 62 to 65 as the region most likely to form this epitope. An unabsorbed rabbit antiserum raised against a peptide corresponding to residues 56 to 69 of HLA-A2 gives highly specific reactions with HLA-A2 and HLA-B17 heavy chains in Western blots. No interactions with native HLA-A2 and B17 molecules were detected in a variety of assays. Although the topographic relationship between the epitopes recognized by the rabbit antiserum and the monoclonal antibody could not be determined, the results show that residues 56 to 69 of HLA-A2 can form epitopes with specificity for HLA-A2 and HLA-B17.

Amino Acid Sequence↗
PubMed1986

Function and cell distribution of KC-1, a novel natural killer cell-associated antigen.

Natural killer (NK) cell have been implicated in immune responses to tumor and viral antigens. We describe here a monoclonal antibody, anti-KC-1, that blocks lysis of NK targets by fresh but not activated NK cells. Anti-KC-1 has no effect on cytotoxic T lymphocyte activity or on antibody-dependent cellular cytotoxicity. This antibody may be useful in the analysis of NK cell activation and the mechanism of lysis.

Animals↗
PubMed1986

Further studies on the epitopes of HLA-B7 defined by murine monoclonal antibodies.

Monoclonal antibodies reactive with polymorphic epitopes of HLA-B7 were analyzed by direct and indirect cytotoxicity assays on established panels of HLA typed lymphocytes. This permitted further refinement of their specificity and the identification of various novel reactions. The topographic relationship of polymorphic epitopes on the surface of the B7 molecule was assessed with various serological assays using cell surface B7 or papain solubilized B7 as the antigenic target. These studies focused on monoclonal antibodies recognizing B27 and B7. The results, in combination with those of previously published studies, are used to provide a current assessment of the epitope map of HLA-B7 as defined with mouse monoclonal antibodies. This is compared to the results obtained with alloantisera.

Animals↗
PubMed1985

Determinants recognized by human cytotoxic T cells on a natural hybrid class I HLA molecule.

The major histocompatibility complex class I HLA molecules are the primary determinants recognized by allogeneic cytotoxic T lymphocytes (CTL), and serve as restricting elements for CTL recognition of viral, chemical, or minor histocompatibility antigens. HLA-Aw69 is a naturally occurring hybrid class I molecule that we have used to investigate the regions of class I antigens involved in human CTL recognition. HLA-Aw69 appears to have resulted from an exon shuffle between two closely related class I genes: the alpha 1 domain of HLA-Aw69 is identical to that of HLA-Aw68, while the alpha 2 and alpha 3 domains are identical to HLA-A2. The determinants recognized by human allogeneic CTL clones specific for HLA-A2, -Aw68, and/or -Aw69 fall into three patterns: (a) CTL determinants are located on both the alpha 1 and alpha 2 domains; (b) interaction of the alpha 1 and alpha 2 domains results in new combinatorial determinants; (c) interaction of the alpha 1 and alpha 2 domains in the hybrid molecule results in the loss of CTL determinants that are present on both parental molecules. Thus, using human CTL clones, target cells, and HLA molecules, we show that the interaction of the alpha 1 and alpha 2 domains alters CTL determinants in ways not directly predictable from primary structure.

Amino Acid Sequence↗
PubMed1985

The complete primary structure of HLA-Bw58.

Serological studies indicate that HLA-B17 molecules are unusually cross-reactive with products of the HLA-A locus. In particular, a mouse monoclonal antibody MA2.1 defines an epitope that is shared by HLA-A2 and the two subtypes (Bw57 and Bw58) of B17. To investigate these relationships at the structural level, we have isolated a gene coding for Bw58 from the WT49 B cell line. The gene was transfected into mouse L cells and its protein product was characterized with a panel of monoclonal anti-HLA antibodies. The nucleotide sequence of 3520 base pairs of DNA encompassing the seven exons coding for Bw58 and associated introns was determined. The deduced protein sequences for Bw58 and eight other HLA-A,B,C molecules were compared. In the first polymorphic domain (alpha 1), Bw58 is unusual in that it is as homologous to HLA-A locus products as to HLA-B locus products. In the second polymorphic domain (alpha 2), Bw58 has greater homology to B locus products. In the alpha 1 domain of Bw58, small segments of amino acid and nucleotide sequence homology with A2 (residues 62-65) and with Aw24 (residues 75-83) are found in the major region of polymorphic diversity (residues 62-83). These similarities provide structural correlates for the serological relationships between Bw58 and A locus molecules, with residues 62-65 possibly being involved in the MA2.1 epitope. From comparisons of four HLA-A and four HLA-B sequences, there is a difference in the patterns of variation for A and B locus molecules. For B locus molecules there is greater variation in the alpha 1 domain than in the alpha 2 domain. For A locus molecules, variation in the two domains is similar and like that for B locus alpha 2 domains. In comparison to other HLA-A,B,C genes, novel inverted repeat sequences were found in the nucleotide sequence of HLA-Bw58. These sequences flank the putative RNA splicing sites at the 3' end of the exons encoding the alpha 2 and alpha 3 protein domains.

Amino Acid Sequence↗
PubMed1985

Importance of immunoglobulin isotype in human antibody-dependent, cell-mediated cytotoxicity directed by murine monoclonal antibodies.

Using the fluorescence activated cell sorter to select rare IgG2a- and IgG2b-producing variants, we developed switch variant families of hybridomas from IgG1-producing hybridomas, ME1 and MA2.1. The IgG2a and IgG2b antibodies produced by such switch variants have the same binding activities for HLA as the IgG1 antibodies produced by the parent hybridomas. Using these antibodies, we directly compared the IgG1, IgG2a, and IgG2b murine Ig isotypes for their capacities to direct human peripheral blood lymphocytes (PBL) in antibody-dependent cell-mediated cytotoxicity (ADCC) against a B lymphoblastoid cell line. We demonstrate that, for antibodies of identical binding affinity and specificity, the murine IgG2a isotype is the most effective in directing ADCC by human effector cells. The murine IgG2b directs intermediate levels of ADCC activity while IgG1 is inactive. We identified the effector cells in human PBL that mediate IgG2a or IgG2b ADCC as nonadherent killer (K) cells. These cells express the C3bi receptor and have cytolytic activity which is specifically blocked by a monoclonal antibody (anti-Leu-11a) that binds the Fc receptor (FcR) of such cells. Finally, FcR-bearing K cells bind to target cell-bound, rather than free, IgG2a or IgG2b molecules.

Animals↗