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Biomedical subjects

A H Johnson

Publications and source records attributed to A H Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Development of a malaria T-cell vaccine for blood stage immunity.

We have defined a strategy for the development of a T-cell vaccine for blood stage immunity, taking into consideration the central role of T cells and MHC restriction in malaria immune responses. We have used the AMPHI computer algorithm to identify putative T-cell epitopes from conserved regions of 11 Plasmodium falciparum asexual stage proteins. Ten of the eleven proteins are currently candidates for vaccine development. Using this algorithm we selected 22 putative T-cell epitope peptides and 8 control peptides. These peptides were used to test the T-cell responses of three defined populations of Caucasians who have (1) recovered from P. falciparum malaria, (2) been exposed, but never clinically infected, (3) never been exposed or infected. Preliminary analysis of our data shows population differences in T-cell responses to putative T-cell epitope peptides. Ultimately, these studies will help to identify those T epitopes that can be incorporated into a T-cell vaccine for protective immunity.

Animals↗
PubMed1992

Alterations in cellular cholesterol metabolism following administration of 6-hydroxydopamine to rabbits.

1. The role of adrenergic mechanisms in the regulation of cholesterol metabolism was investigated by studying the effects of 6-hydroxydopamine (6-OHDA) on serum cholesterol levels and on the activities of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, acyl coenzyme A: cholesterol-O-acyl-transferase (ACAT) in the livers and intestines, and cholesterol 7 alpha-hydroxylase in the livers of male New Zealand White rabbits. 2. Total serum cholesterol levels were significantly reduced (P less than 0.01) in 6-OHDA-treated animals. This was reflected in the very low density lipoprotein, low density lipoprotein and high density lipoprotein fractions. The reduction in lipoprotein cholesterol levels reflected reduced cholesterol proportions in the lipoprotein fractions. 3. The 6-OHDA-treated animals also had significantly lower activities of intestinal (P less than 0.001) and hepatic (P less than 0.01) HMGCoA reductase. The specific activities of intestinal ACAT, hepatic ACAT and cholesterol 7 alpha-hydroxylase were comparable in both groups. 4. In contrast to the results observed in vivo, 6-OHDA did not have any in vitro effect on cholesterol biosynthesis in cultured human leucocytes. 5. This latter finding suggests that the effects of 6-OHDA on cellular cholesterol biosynthesis in vivo are indirect, possibly resulting from the known toxic effect of this drug in sympathetic nerve terminals, and imply a potential role for the sympathetic nervous system in the regulation of cellular cholesterol biosynthesis in vivo.

Animals↗
PubMed1991

Mutations affecting antigen processing impair class II-restricted allorecognition.

Both exogenously derived and endogenously derived Ag generally require processing for their optimal binding and presentation by class I and class II major histocompatibility proteins. It is not known whether steps involved in Ag processing also affect the recognition of alloreactive T cells. We have recently described B cell mutants which have general defects in the processing and presentation of a variety of exogenous Ag to class II restricted T cells. In this report we have studied the ability of these processing mutants to stimulate a set of anti-DR3-specific alloreactive T cells clones. These processing/presentation mutants express normal MHC class II molecules, both in terms of primary sequence and cell surface abundance, but they appear unable to generate effective peptide-MHC complexes. When tested for their ability to stimulate MHC class II alloreactive T cell clones, only one of four T cell clones was stimulated by these mutants; the other three alloreactive T cell clones were not stimulated by either of two different mutants. Both of these mutants express normal levels of the accessory molecules, LFA-3 and ICAM-1. The inability of these mutants to stimulate three of four alloreactive clones indicates that the capacity to be recognized by many alloreactive T cells is linked to the Ag processing capacity of a stimulator cell.

Antigen-Presenting Cells↗
PubMed1991

Heterogeneity of the T-cell receptor beta gene rearrangements generated in myelin basic protein-specific T-cell clones isolated from a patient with multiple sclerosis.

Seventeen T-cell clones derived from the peripheral blood of a patient with multiple sclerosis and reactive with a synthetic peptide corresponding to residues 152-170 of the human myelin basic protein molecule were previously shown to be cytotoxic for myelin basic protein-coated target cells. Genetic restriction studies have now demonstrated that these clones recognize myelin basic protein in association with human leukocyte antigen DRw13. Studies of the T-cell receptor beta gene rearrangements generated by these clones demonstrated 12 different patterns, as evaluated by Southern blot analysis. Thus, the human T-cell response to myelin basic protein is exceedingly heterogeneous, even among T cells that recognize the same small fragment of the molecule in association with the same class II restriction element.

Clone Cells↗
PubMed1991

Serum lipoproteins and cholesterol metabolism in two hypercholesterolaemic rabbit models.

Serum lipoproteins and key hepatic and intestinal enzymes regulating cholesterol synthesis, esterification and catabolism, namely 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, acyl coenzyme A: cholesterol-o-acyltransferase (ACAT) and cholesterol 7 alpha-hydroxylase respectively, were compared in two hypercholesterolaemic rabbit models - the cholesterol-fed animal and the hypercholesterolaemic diabetic animal. Hypercholesterolaemia in the cholesterol-fed animals was reflected in the VLDL and LDL fractions, whereas VLDL and HDL2 cholesterol levels were elevated in the diabetic animals. The lipoproteins of the cholesterol-fed animals were enriched with cholesterol but the lipoprotein fractions in the diabetic animals were enriched with triacylglycerol. While hepatic HMGCoA reductase activity was significantly reduced in both groups, the activities of hepatic ACAT and cholesterol 7 alpha-hydroxylase were significantly increased in the cholesterol-fed animals and significantly reduced in the diabetic animals compared with controls. In the intestine, the activity of HMGCoA reductase was increased and ACAT reduced in the diabetic animals. By contrast, in the cholesterol-fed group. HMGCoA reductase activity was lower and ACAT activity was higher in comparison with the control group. These differences in lipoproteins and cellular cholesterol metabolism between the hypercholesterolaemic rabbit models may explain the differences in susceptibility to atherosclerosis, previously reported in these two animal models.

Animals↗
PubMed1991

DRw8 microvariation: a new DRB1 allele identified in association with DQw7 in American blacks.

In the American black population, DRw8 is commonly found in association with DQw7 and an undefined HLA-D specificity. Polymerase chain reaction amplification was used to obtain DRB1 cDNA clones from two unrelated individuals expressing this haplotype. The DRB1 sequence is most similar to a sequence found in cells expressing DRw8, DQw4, Dw8.2 differing at the protein level by a single amino acid substitution at position 86.

Alleles↗
PubMed1991

DRw11 haplotypes: continuum of DRB1 diversity augmented by unique DQ/DRw52 associations.

cDNA sequencing of the first domains of DRB1, DRB3, DQA1, and DQB1 alleles was used to examine the extent of diversity in American black individuals expressing several DRw11 haplotypes. In addition to previously described DRw11 alleles, DRB1*1102 and DRB1*1103, two new DRB1 alleles, DRB1*11012 and DRB1*11042, were identified which differ from previously described alleles at the nucleic acid but not at the protein level. Gene conversion-like events have likely generated the DRw11 microvariation resulting in the merging of DRw11 with the DRw13 allele family. The DRw11 alleles are associated with various DQ alleles: DQw1 (DQw5 and DQw6), DQw7, and a serologically undefined DQ allele. This undefined DQ molecule, comprised of a DQ alpha/beta combination encoded by a DQw7 alpha gene (DQA1*0301) and a DQw2 beta gene (DQB1*0201), was previously observed in some DR7 and DR9 haplotypes. DRw11 haplotype diversity is augmented by the association of one of the DRw11 alleles with the DRw52c allele in contrast to the more common DRw11, DRw52b association. The extensive diversity exhibited by the DRw11 and DRw13 family of haplotypes coupled with their high frequency in populations of African ancestry suggest that the DRw11/w13 allele family may be very old and/or that these haplotypes carry some selective advantage.

Amino Acid Sequence↗
PubMed1991

The impact of naturally occurring DR3 microvariants, DRw17 and DRw18, on T-cell allorecognition.

The limited amino acid sequence differences between the DR3 microvariants, DRw17 and DRw18, are found in the second variable region of the DR beta chain (residues 26 and 28) as well as in framework residues 47 and 86. Using selected responder/stimulator combinations, alloproliferative T-lymphocyte clones (TLC) were generated which recognize either a supertypic DR3-related determinant(s) or only those T-cell recognition determinants created by the four amino acids which differ between DRw17 and DRw18. Results indicate that the microvariation creates potent T-cell recognition determinants while leaving the DR3-related determinant(s) unaffected. Several TLC were generated which recognize the DRw18 molecule strongly and the DRw52c molecule weakly reflecting the sequence similarity between these molecules. In addition, one TLC was generated which recognizes DRw18 and DRw14,Dw9 but not DRw14,Dw16 molecules, a result not predicted by linear amino acid sequence comparisons. The intricate and sometimes unpredictable allorecognition patterns observed demonstrate that the molecular context of a specific amino acid sequence is as important as the actual sequence in forming a T-cell recognition site and, thus, in shaping the immune response profile of a given allele.

Antibodies, Monoclonal↗
PubMed1990

Two divergent routes of evolution gave rise to the DRw13 haplotypes.

The HLA class II genes and haplotypes have evolved over a long period of evolutionary time by mechanisms such as gene conversion, reciprocal recombination and point mutation. The extent of the diversity generated is most clearly evident in an analysis of the HLA class II alleles present within DRw13 haplotypes. This study uses cDNA sequencing to examine the first domains of DRB1, DRB3, DQA1, and DQB1 alleles from several American black individuals expressing seven different DRw13 haplotypes, five with undefined HLA-D specificities (i.e., not Dw18 or Dw19). Two new DRw13 alleles described in this study are the first examples of convergent evolution of DR alleles in which gene conversion has apparently combined segments of DRB1 alleles encoding DRw11 and DRw8 to generate two new DRB1 alleles, DRB1*1303 and DRB1*1304, that encode molecules bearing serologic determinants of a third allele, DRw13. These new DRw13 alleles are found embedded in haplotypes of DRw11 origin distinct from haplotypes encoding previously identified DRw13 alleles, DRB1*1301 and DRB1*1302. These data suggest that two evolutionary pathways may have given rise to two subgroups of alleles encoding molecules that share DRw13 serologic determinants yet which possess different structural and, likely, functional motifs. Reciprocal gene recombination events resulting in different DR, DRw52 and DQ allele combinations also appear to have played a crucial role in augmenting the level of diversity found in DRw13 haplotypes. Recombination has resulted in the association of one of the new DRw13 alleles with a DQw2 allele normally found associated with DR7 and the association of the DRw52c-associated DRw13 allele (DRB1*1302) with three different DQw1 alleles. The seven DRw13 haplotypes that have resulted from the effect of recombination on haplotypes formed by the two pathways of DRw13 allelic diversification have resulted in different repertoires of class II molecules and, most likely, different immune response profiles in individuals with these haplotypes.

Alleles↗
PubMed1990

Complotypes in individuals of African origin: frequencies and possible extended MHC haplotypes.

We analyzed the frequency distribution of 106 complotypes [four allele sets of the major histocompatibility complex (MHC) genes for the complement proteins factor B, C2, C4A, and C4B] from 32 Black families residing in Boston and Washington, DC. Twenty-five different complotypes were identified, among which there were four complotypes that had not been previously observed in our large database of complotypes compiled from family studies of Boston Caucasians and that are, presumably, unique to individuals of African origin. These four African-derived complotypes are FC(1,90)0, FC63, S1C2, 17, and SC(3,2,90)0. The frequencies of two of these four unique Black complotypes, FC(1,90)0 and FC63, were increased significantly when compared to Caucasians (pcorr less than 0.00042, pcorr = 0.00294, respectively). The complotype FC(1,90)0 was in positive linkage disequilibrium with HLA-DR3 haplotypes containing the B locus antigens Bw42, Bw52, Bw53, and Bw58, while FC63 was associated with HLA-Bw70, -DR5. These findings demonstrate the extensive polymorphism of complotypes in Blacks, and also suggest that it may be possible to define unique extended haplotypes of African origin.

Alleles↗
PubMed1990

The complexity of DRw6 and DR5 haplotypes in American blacks demonstrated by serology, cellular typing, and restriction fragment length polymorphism analysis.

This study describes the diversity of DRw6 and DR5 haplotypes in the American black population using serology, cellular typing, and restriction fragment length polymorphism (RFLP) analysis. DRw6 (DRw13 and DRw14) and DR5 (DRw11 and DRw12) haplotypes are observed at a high frequency in this population (DRw6: 32%, DR5: 30%). Many of these haplotypes express undefined HLA-D specificities and unusual DQ and DRw52 associations which previously have not been well characterized or reported (e.g., DRw13, DQw5, DRw52c, D-; DRw13, DQw2, DRw52a, D-; DRw11, DQw5, DRw52c, D-). Serologic analysis of class II alleles in American blacks suggests the presence of DRw13, DRw11 and DQw6 allelic variants and demonstrates the difficulty in defining DRw6 and DR5 in this population. The class II genes from four American black families expressing many of the novel DRw13, DRw14, DRw11, and DRw12 haplotypes defined by serology and mixed leukocyte culture were further characterized by RFLP analysis. The data presented here along with other published data identify at least eight DRw13 haplotypes (DRw13A-DRw13H) in the human population. Five of these haplotypes exhibit an undefined HLA-D specificity. Three DRw14 haplotypes (DRw14A-DRw14C) and eight DR5 haplotypes (DRw11A-DRw11E and DRw12A-DRw12C) were also identified. The novel DRw6 and DR5 haplotypes observed in American blacks may arise from differences in DRB1, DQA1, and DQB1 genes as well as from differences in the combinations of alleles of these genes encoded by a haplotype. The serologic and RFLP analyses suggest that some DRw13 and DRw11 haplotypes represent transitional steps between DRw13 and DRw11 in the evolutionary pathway which generated the DRw52 family.

Antibodies, Monoclonal↗