The haptoglobin-gene deletion responsible for anhaptoglobinemia.

We have found an allelic deletion of the haptoglobin (Hp) gene from an individual with anhaptoglobinemia. The Hp gene cluster consists of coding regions of the alpha chain and beta chain of the haptoglobin gene (Hp) and of the alpha chain and beta chain of the haptoglobin-related gene (Hpr), in tandem from the 5' side. Southern blot and PCR analyses have indicated that the individual with anhaptoglobinemia was homozygous for the gene deletion and that the gene deletion was included at least from the promoter region of Hp to Hpr alpha but not to Hpr beta (Hpdel). In addition, we found seven individuals with hypohaptoglobinemia in three families, and the genotypes of six of the seven individuals were found to be Hp2/Hpdel. The phenotypes and genotypes in one of these three families showed the father to be hypohaptoglobinemic (Hp2) and Hp2/Hpdel, the mother to be Hp2-1 and Hp1/Hp2, one of the two children to be hypohaptoglobinemic (Hp2) and Hp2/Hpdel, and the other child to be Hp1 and Hp1/Hpdel, showing an anomalous inheritance of Hp phenotypes in the child with Hp1. The Hp2/Hpdel individuals had an extremely low level of Hp (mean+/-SD = 0.049+/-0. 043 mg/ml; n=6), compared with the level (1.64+/-1.07 mg/ml) obtained from 52 healthy volunteers having phenotype Hp2, whereas the serum Hp level of an individual with Hp1/Hpdel was 0.50 mg/ml, which was approximately half the level of Hp in control sera from the Hp1 phenotype (1.26+/-0.33 mg/ml; n=9), showing a gene-dosage effect. The other allele (Hp2) of individuals with Hp2/Hpdel was found to have, in all exons, no mutation, by DNA sequencing. On the basis of the present study, the mechanism of anhaptoglobinemia and the mechanism of anomalous inheritance of Hp phenotypes were well explained. However, the mechanism of hypohaptoglobinemia remains unknown.     

Isolation and characterization of bovine haptoglobin from acute phase sera

A macromolecular hemoglobin-binding protein, which was not detectable in normal bovine sera but appeared during acute phase inflammation, was purified, characterized, and designated as bovine haptoglobin (Hp). The purified protein had a molecular mass of 1,000-2,000 kDa, and was composed of two kinds of peptides, a 20-kDa peptide (alpha chain) and a 35-kDa glycopeptide (beta chain) linked by disulfide bonds. Amino acid composition and N-terminal sequence analyses revealed that both peptides were homologous to each counterpart of human Hp. Studies using some reducing reagents proved that highly polymerized Hp in serum was composed of 2-20 polymerized forms of alpha 2 beta 2 tetramer. Hp could bind one molecule of hemoglobin/alpha 2 beta 2 unit. Hp with smaller sizes obtained from native Hp by partial reduction with cysteine showed almost the same Hb-binding capacity.     

Cloning and expression of human haptoglobin subunits in Escherichia coli: delineation of a major antioxidant domain

Human plasma haptoglobin (Hp) comprises alpha and beta subunits. The alpha subunit is heterogeneous in size, therefore isolation of Hp and its subunits is particularly difficult. Using Escherichia coli, we show that alpha1, alpha2, beta, and alpha2beta chain was abundantly expressed and primarily present in the inclusion bodies consisting of about 30% of the cell-lysate proteins. Each cloned subunit retained its immunoreactivity as confirmed using antibodies specific to alpha or beta chain. By circular dichroism, the structure of each expressed subunit was disordered as compared to the native Hp. The antioxidant activity was found to be associated with both alpha and beta chains when assessed by Cu(2+)-induced oxidation of low density lipoprotein (LDL). Of remarkable interest, the antioxidant activity of beta chain was extremely potent and markedly greater than that of native Hp (3.5x), alpha chain (10x) and probucol (15x). The latter is a clinically proved potent compound used for antioxidant therapy. The "unrestricted" structure of beta subunit may therefore render its availability for free-radical scavenge, which provides a utility for the future design of a "mini-Hp" in antioxidant therapy. It may also provide a new insight in understanding the mechanism involved in the antioxidant nature of Hp.     

Clearance of certain modified haptoglobins from the rabbit circulation

1. Human haptoglobin (Hp) type 2-1 was subjected to the sulfanilazo-modification of tyrosine and histidine residues, the removal of sialic acid, and the reduction of disulfide bonds (isolation of alpha 2, alpha 1, beta subunits), respectively. Radioactively labeled preparations were administered intravenously to rabbits. 2. Human Hp and isolated beta (heavy) chain disappeared from the circulation somewhat faster (half-lives = 72 and 67 h, respectively), than homologous rabbit Hp (half-life = 96 h). Hp light chains (alpha 2, alpha 1), devoid of oligosaccharide showed shorter half-lives of 27-19 h. 3. Treatment of Hp with diazotized sulfanilic acid resulted in an appreciable reduction of half-life to 21-11 h, as dependent on the number of modified residues. 4. Asialo-Hp, asialo-beta chain, and asialo-sulfanilazo-Hp were cleared rapidly from the circulation with half-lives of 5.5, 5.0, and 4.2 h, respectively. 5. These results suggest that in different pathways of Hp catabolism in vivo, polypeptide recognition markers in addition to carbohydrate ones, are involved.     

Studies on free or haptoglobin-bound hemoglobin and derivatives (semihemoglobins and porphyrinated semihemoglobins). Some aspects of their peroxidatic activity.

The peroxidatic activity of hemoglobin (Hb) is known to be enhanced when this hemoprotein is bound to haptoglobin (Hp). The peroxidatic reaction (H2O2, guaiacol as donor) has been kinetically studied (Steady-state) in the presence of free or rabbit-haptoglobin bound human hemoglobin and some of its derivatives, all in ferricyano-form. With free Hb+ CN, we observed linearity of Lineweaver and Burk plots in a wide range of concentrations, the donor's behaviour was therefore assumed to obey the Michaelis-Menten mechanism. When Hp-Hb+ CN is the enzyme, the donor's behaviour is more complicated, analysis shows the existence of two kinds of donor's binding sites. The possibility whether this behaviour might correspond to the intrinsic properties of Hb chains, as revealed after combination with Hp, was examined. The peroxidatic activity of free and Hp-bound alpha and beta chains of Hb were studied. The alpha chains of Hb combine with Hp whereas the beta chains fail to do so. In order to make useful comparisons, the peroxidatic activity of Hp-bound alpha and beta chains were studied by the use of Hp-semihemoglobin complexes where the semihemoglobins carried heme on only one type of chain (alpha or beta). Results did not show an evident correlation between the activities of the two free or bound types of chains and those of the two classes of binding sites revealed in Hp-Hb+ CN. Moreover, it appeared that the heme-free complementary chain might influence the activity of the heme-carrying alpha or beta chain in semihemoglobins and Hp-semihemoglobin complexes. The binding or protoporphyrin on free and Hp-bound semihemoglobins leads to species which exhibit structures close to that of Hb and Hp-Hb complex respectivley. Results of studies on these derivatives brought up new interesting data : when the porphyrin ring alone is bound to the heme deficient chains (alpha or beta), in Hp-semihemoglobin complexes, the same peculiar behaviour, already observed with Hp-Hb complex, is found again. The structural implications of these results are discussed.     

Molecular cloning of human haptoglobin cDNA: evidence for a single mRNA coding for alpha 2 and beta chains

Human haptoglobin (Hp) is a plasma glycoprotein composed of alpha and beta polypeptide chains that are covalently associated by disulfide bonds. It had been suggested that alpha and beta polypeptides could be synthesized via a common precursor polypeptide. We report the molecular cloning of DNA complementary to human Hp mRNA. One of the clones, pULB1148, carries a full length copy coding for both alpha 2 and beta polypeptides. In vitro translation of human liver mRNA hybridizing with this cDNA gives a protein mol. wt. of 49000 daltons. The sequence of the alpha 2 beta cDNA shows the presence of a single Arg residue between Gln 142 of the alpha 2 chain and Ileu 1 of the beta chain. With a few minor exceptions, the DNA sequence fits the previously published amino acid sequences. The differences are the presence of an Asp residue at position 52 of alpha 2 instead of Asn, the existence in beta of only one Lys residue between Gly 65 and the following Gln, the presence of Ser and Cys at positions 218-219 instead of Cys-Ser, and of Asp residues at positions 205 and 235 instead of Asn.     

Haptoglobin polymorphism--not only a genetic marker]

The biological activities of the haptoglobin polymorphism are controlled by continuous DNA sequences coding for the HP alpha and Hp beta polypeptide chains and forming with a linked Hp related gene the haptoglobin gene complex on chromosome 16. Probably, this DNA domain originates from the gene family of the serine proteases after having lost the informations for the proteolytic functions. Instead of this, the haptoglobins have acquired other qualities, among them the hemoglobin binding capacity, inserted into the Hp beta chain. The Hp polymorphism is constituted by the evolutionary progressive DNA sequences for the Hp alpha chains, which probably have activation functions. The haptoglobins display immunoregulative abilities, which can be immunosuppressive by inhibition of the lymphocyte reactivity or immunoinductive by influencing the IgM biosynthesis, adapted to the functional requirements. In this field, Hp 2-2 has a stronger effect than the two other Hp types. Moreover, the haptoglobins inhibit the prostaglandin synthesis and protect against harmful oxidation processes. These qualities are based on the hemoglobin binding ability and can be realized by Hp 1-1 with the comparatively highest efficacy. Further on, the haptoglobins are protease inhibitors. Finally, Hp 2-2 is associated with higher albumin and ceruloplasmin serum levels than Hp 2-1 and Hp 1-1. Evidently, the haptoglobins are inserted into a widely ramified network of biological functions. The selective advantages and disadvantages of the Hp polymorphism are noticeable under pathological conditions in case of malignant tumors, inflammations, autoimmune diseases, allergic illness, affective psychoses and affective lability favouring addiction.     

Determination of haptoglobin genotype in an Iranian population with idiopathic generalized epilepsy

Background:

Haptoglobin (Hp) is a plasma α₂-sialoglycoprotein that contains alpha and beta chains. It displays in three common phenotypes, Hp1-1, Hp2-1, and Hp2-2. Proteins expressed by polymorphic genes have grossly different molecular sizes resulting in different diffusion rates in the brain. Haptoglobin expressed by the Hp2-2 genotype has lower hemoglobin-binding capacity than Hp1-1 or Hp2-1 and is associated with idiopathic generalized epilepsy.

Methods:

To determine polymorphism in haptoglobin genes in patients with idiopathic generalized tonic-clonic seizures, 42 men, 42 women, and 50 controls were selected for this study. Genomic DNA was extracted from blood and studied by polymerase chain reactions (PCR).

Results:

The amplified fragments for the Hp1-1 and Hp2-2 genotypes were 1757 and 3481 base pairs (bp) respectively, and the Hp2-1 genotype had both fragments, in addition to a 349-bp fragment. The distribution of the three major Hp phenotypes in epilepsy patients was 28.6 (1-1), 38.1 (2-1), and 33.3% (2-2) in the men, and 31 (1-1), 40.5 (2-1), and 28.6% (2-2) in the women. The distribution of Hp genotypes in controls was 22 (1-1), 40 (2-1), and 38% (2-2).

Conclusion:

We show that all Hp genotypes participate in idiopathic generalized epilepsy.Key Words: Epilepsy, Haptoglobin, Iran     

Evolution of haptoglobin: comparison of complementary DNA encoding Hp alpha 1S and Hp alpha 2FS.

Haptoglobin is a transport glycoprotein which removes free hemoglobin from the circulation of vertebrates. In human populations haptoglobin is polymorphic due to three alleles, Hp alpha 1F, Hp alpha 1S and Hp alpha 2. The Hp alpha 2 allele is roughly twice the length of the Hp alpha 1 alleles and is the product of a partial gene duplication possibly resulting from an unequal crossover event in a heterozygous genotype Hp alpha 1F/Hp alpha 1S. In the study described here we compare the cDNA encoding Hp alpha 1S to that encoding Hp alpha 2FS . Both have a leader sequence followed by the genotypic alpha chain sequence, a beta sequence and an untranslated sequence in the 3' end. The cDNA encoding Hp alpha 2FS is composed of alpha 1F and alpha 1S domains differing by four nucleotide replacements. Hp alpha 1S cDNA contains the same replacement site mutations found in the alpha 1S domain of Hp alpha 2FS , indicating that this coding region has sustained few, if any, mutations since its incorporation into the Hp alpha 2FS gene.     

Hemoglobin-binding site on human haptoglobin. Identification of lysyl residues participating in the binding.

The locus of human haptoglobin (Hp) molecules that interacts with human hemoglobin (Hb) was examined by the differential labeling technique. First, amino groups of Hp were extensively labeled with ethyl acetimidate (EAI) either in the free state (experiment A) or in the equimolar complex with Hb (experiment B). Each of the labeled Hp samples was reduced and S-carboxymethylated, and the remaining amino groups were then allowed to react with trinitrobenzenesulfonic acid (TNBS) under denatured conditions. Only 0.6 mol/mol of the trinitrophenyl (TNP) group was introduced into the heavy chain of Hp in experiment A, whereas 2.5 mol/mol of TNP groups were into the same chain in experiment B. The extent of TNP modification for the light chain was very low in either of the experiments. The amino acid residues carrying TNP groups in the heavy chain were identified by the peptide mapping procedure. They were Ile1, Lys136, and Lys218 in experiment B, and only Ile1 in experiment A. These findings suggest that epsilon-amino groups of Lys136 and Lys218 in the heavy chain are both situated within the Hb-binding locus of Hp, and that the alpha-amino group of Ile1 is buried inside the molecule either in the presence or absence of Hb.     

Structure and evolution of artiodactyla haptoglobins.

1. Artiodactyla haptoglobins (Hps), goat, sheep and cattle (family Bovidae), and pig (family Suidae) were structurally characterized. 2. The polymeric Hp systems of goat, sheep and cattle were similar to the polymeric human Hp system, while the monomeric system of pig was more comparable to the monomeric human form. 3. All members of the Artiodactyla (family Bovidae) examined exhibited a large polypeptide subunit, comparable to that of the beta subunit of human Hp. 4. In addition, a small subunit, similar in molecular weight to the human alpha 2 subunit, was demonstrated. Pig Hp was shown to have two subunits, one slightly larger than the human beta subunit and the other intermediate in size to the human alpha 1 and alpha 2 subunits. 5. Immunoelectrophoretic and immunodiffusion studies indicated complete cross reactivity among the polymeric Artiodactyla Hps. 6. The polymeric Hps do not, however, cross react with the monomeric pig Hp.     

Evidence of tandem repeat and extra thiol-groups resulted in the polymeric formation of bovine haptoglobin: a unique structure of Hp 2-2 phenotype

Human plasma Hp is classified as 1-1, 2-1, and 2-2. They are inherited from two alleles Hp 1 and Hp 2, but there is only Hp 1 in almost all the animal species. Hp 2-2 molecule is extremely large and heterogeneous associated with the development of inflammatory-related diseases. In this study, we expressed entire bovine Hp in E. coli as a alphabeta linear form. Interestingly, the antibodies prepared against this form could recognize the subunit of native Hp. In stead of a complicated column method, the antibody was able to isolate bovine Hp via immunoaffinity and gel-filtration columns. The isolated Hp is polymeric containing two major molecular forms (660 and 730 kDa). Their size and hemoglobin binding complex are significantly larger than that of human Hp 2-2. The amino-acid sequence deducted from the nucleotide sequence is similar to human Hp 2 containing a tandem repeat over the alpha chain. Thus, the Hp 2 allele is not unique in human. We also found that there is one additional -SH group (Cys-97) in bovine alpha chain with a total of 8 -SH groups, which may be responsible for the overall polymeric structure that is markedly different from human Hp 2-2. The significance of the finding and its relationship to structural evolution are also discussed.     

Purification of human plasma haptoglobin by hemoglobin-affinity column chromatography

Haptoglobin (Hp) is an acute-phase protein; its plasma levels increase consistently in response to infection and inflammation. The concentration of human plasma Hp is ranged between 1 and 1.5 mg/ml. Similar to blood type, individual human Hp is classified as Hp 1-1, 2-1, or 2-2. The structural and functional analysis of the Hp, however, has not been studied in detail due to its difficult isolation procedure. Previously, we reported a single step for the purification of porcine Hp. In this study, we established a purification method using a high capacity hemoglobin-affinity column. Briefly, DEAE-purified human hemoglobin was first coupled to Sepharose 4B to prepare an affinity column in a 15-ml bed volume. Following a flow through of human plasma and an extensive wash, the bound material was eluted with a solution of 0.15 M NaCl, pH 11 (adjusted by ammonium), to remove low-affinity bound proteins. The high-affinity bound Hp was then eluted with 0.15 M NaCl containing 5 M urea, pH 11, and collected in tubes containing 100 microl of 1 M Tris buffer, pH 7.0. The biological activity of dialyzed Hp was retained as it formed a complex with hemoglobin on a sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Using this procedure, approximately 10 mg of Hp 1-1, with homogeneity greater than 96%, was obtained from 15 ml of human plasma. Affinity purified Hp 2-1 or 2-2, however, contained trace amounts of apoA-I with the similar approach. The Hp could be further purified by HPLC using a Superose 12 gel-permeation chromatography, if desired, to achieve 100% purity. All the phenotypes of purified Hp consisted of alpha and beta chains on SDS-PAGE in the presence of a reducing reagent, further confirmed by a Western blot analysis. We conclude that human hemoglobin-affinity column was most suitable for the isolation of Hp 1-1 in large quantities. Whereas, one additional step using a gel-permeation was necessary for that of Hp 2-1 and 2-2.     

Amino acid sequence and disulfide-bridge location of canine haptoglobin.

The complete amino acid sequence and disulfide-bridge location of canine haptoglobin (Hp) were determined by analyzing various fragments produced chemically and/or enzymatically. Canine Hp consists of two light (L) and two heavy (H) chains with 83 and 245 amino acid residues, respectively. It has three potential oligosaccharide-binding sequences, Asn-X-Ser/Thr, one in the L chain and two in the H chain. All of them are glycosylated. Comparison of the amino acid sequences between canine Hp and human Hp shows 68 and 85% homology for L chains and H chains, respectively. About 20% of the canine L chain still retains a carboxyl-terminal arginine residue, which is completely removed during maturation in human L-chain. The half-cystine residue at position 15 in the L chain, which participates in the inter-L chain disulfide bridging in human Hp, has been replaced by a leucine residue in canine Hp. Therefore, an LH unit in canine Hp may be joined to another LH unit by a noncovalent (mainly hydrophobic) interaction to form the complete molecule. The disulfide bridges in canine Hp link Cys-34L to Cys-68L, Cys-72L to Cys-105H, Cys-148H to Cys-179H, and Cys-190H to Cys-220H, as in the case of human Hp.     

A polymeric form of haptoglobin in the gamma-irradiated Spanish goat

The haptoglobins (Hp) of control and gamma-irradiated Spanish goats were examined. Polyacrylamide gel electrophoresis and Sephadex G-200 chromatography of sera demonstrated that unirradiated controls were ahaptoglobinemic, while irradiated animals developed high Hp levels. An electrophoretic comparison with human Hp phenotypes revealed that goat Hp more closely resembled human Hp 2 than the other two human phenotypes. No electrophoretic band comparable to human Hp 1 appeared in the goat electrophoretic pattern. When goat Hp was tested by immunodiffusion with antiserum to human Hp, no reactivity was observed; however, goat Hp and the three human Hps bound goat, human, and chicken hemoglobins with equal specificity, indicating some degree of structural homology between human and goat Hp. Suggestions as to the effects of irradiation to augment Hp synthesis and speculations about the chain composition and molecular weights of goat Hp are presented.     

Induction of haptoglobin by all-trans retinoic acid in THP-1 human monocytic cell line

Haptoglobin (Hp) is one of the acute-phase proteins and is mainly synthesized in the liver. During our study on the differentiation of leukemia cells, we have found that Hp is synthesized in human monocytic cells by all-trans retinoic acid (ATRA). The synthesis of Hp by ATRA is induced in a dose- and time-dependent manner. Hp cDNA cloned from ATRA-treated THP-1 cells corresponds to the Hp alpha 2(FS)-beta form. Whereas ATRA acted as a strong inducer in THP-1 cells, IL-1 beta, TNF-alpha, IL-6, and LPS had little effect on Hp gene expression in these cells. These findings suggest that THP-1 cells express the Hp gene through a signal pathway different from hepatocytes, and that ATRA is a potent Hp-inducer in these cells.     

Purification of human haptoglobin 1-1, 2-1, and 2-2 using monoclonal antibody affinity chromatography

Similar to blood type, human plasma haptoglobin (Hp) is classified as 3 phenotypes: Hp 1-1, 2-1, or 2-2. The structural and functional relationship between the phenotypes, however, has not been studied in detail due to the complicated and difficult isolation procedures. This report provides a simple protocol that can be used to purify each Hp phenotype. Plasma was first passed through an affinity column coupled with a high affinity Hp monoclonal antibody. The bound material was washed with a buffer containing 0.2M NaCl and 0.02 M phosphate, pH 7.4, eluted at pH 11, and collected in tubes containing 1M Tris-HCl, pH 6.8. The crude Hp fraction was then chromatographed on a HPLC Superose 12 column in 0.05 M ammonium bicarbonate at a flow rate of 0.5 ml/min. The homogeneity of purified Hp 1-1, 2-1, or 2-2 was greater than 95% as judged by SDS-polyacrylamide gel electrophoresis. Essentially, each Hp isolated was not contaminated with hemoglobin and apolipoprotein A-I as that reported from the other methods, and was able to bind hemoglobin. Neuraminidase treatment demonstrated that the purified Hp possessed a carbohydrate moiety, while Western blot analysis confirmed alpha and beta chains corresponding to each Hp 1-1, 2-1, and 2-2 phenotype. The procedures described here represent a significant improvement in current purification methods for the isolation of Hp phenotypes. Circular dichroic spectra showed that the alpha-helical content of Hp 1-1 (29%) was higher than that of Hp 2-1 (22%), and 2-2 (21%). The structural difference with respect to its clinical relevance is discussed.     

Haptoglobin in Carnivora: a unique molecular structure in bear, cat and dog haptoglobins

Haptoglobin (Hp), a hemoglobin-binding protein in plasma, consists of α and β subunits and has a tetra-chain arrangement (β-α-α-β) connected by disulfide bridges in most mammals so far examined. Dog Hp has been reported to be unique compared with other Hps in respect that (1) the two αβ units are joined by a non-covalent interaction rather than a disulfide bridge and (2) the α chain has an oligosaccharide-binding sequence (Asn-X-Ser/Thr) and is glycosylated. To determine whether the unique structures of dog Hp are common in the Carnivora, we purified Hps from sera of bear and cat, and analyzed their subunit structure and partial amino acid sequences. The analyses by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under both reducing and non-reducing conditions, revealed that bear and cat Hps have similar subunit arrangements to dog Hp, suggesting the absence of a disulfide bridge between two α chains. This was confirmed by amino acid sequence analysis of the α chains: that is, Cys₁₅ participating in the inter-α chain disulfide bridge was replaced by Val in bear or Leu in cat and dog. Thus, the unique subunit arrangement of Hp reported in dog may be common in the Carnivora. In contrast to dog Hp, however, α chains of bear and cat Hps were found not to have the typical oligosaccharide binding sequence on their α chains and were not glycosylated.     

DNA polymorphisms in the controlling region of the human haptoglobin genes: a molecular explanation for the haptoglobin 2-1 modified phenotype.

A haptoglobin 2-1 modified (Hp2-1mod) phenotype results when the amount of Hp2 polypeptide synthesized in Hp2/Hp1 heterozygotes is less than that of Hp1 polypeptide. Cloned Hp2 DNA from an individual with the Hp2-1mod phenotype is here shown to have a C in place of the normal A at nucleotide position -61 in one of the interleukin-6 (IL-6) responsive elements of the haptoglobin promoter region. Direct sequencing of the haptoglobin promoter region, amplified by PCR, from DNA from unrelated American blacks showed a C at -61 in all of 10 individuals with the Hp2-1mod phenotype, in two of four with a "possible Hp2-1mod" phenotype, but in none of 15 with the Hp2-1 phenotype. Thus the -61C mutation in the Hp2-61C allele is strongly associated with the Hp2-1mod phenotype. Sequencing results also show that there are three other promoter sequences in the population studied; each can be associated with either Hp2 or Hp1. The variability seen in the Hp2-1mod phenotype, a variability which ranges from close to Hp2-1 to close to Hp1-1, can be explained, in part, by the existence of several Hp2 alleles differing in their promoters--and possibly, in part, by differences in the promoters of the accompanying Hp1 allele. A further part of the variability may be the consequence of differences in the way that the Hp2-61C and the Hp2 alleles respond to the IL-6-dependent factor during an acute-phase response.     

Proteomic analysis of plasma from patients with systemic lupus erythematosus: increased presence of haptoglobin alpha2 polypeptide chains over the alpha1 isoforms

In the present study plasma samples from 15 systemic lupus erythematosus (SLE) patients and 16 healthy controls of initially unknown haptoglobin (Hp) phenotype were separated by 2-DE, and tryptic digests of the excised Hpalpha polypeptide chain spots were analyzed by MALDI-TOF-MS. Selected tryptic peptides were sequenced by nano-(n)ESI-IT MS/MS. The six major Hp phenotypes were present, although with distinct frequencies in controls and SLE patients. Thus, there were an increased proportion of SLE patients with Hp 2-2, or Hp 2-1S phenotypes. The Hp phenotype distribution resulted in allele frequencies of 0 625 (Hp(2)), 0.281 (Hp(1S)), and 0.093 (Hp(1F)) in healthy controls, correlating fairly well with the allele frequencies of European populations. In contrast, the Hp allele frequencies of the SLE patients were 0.733 (Hp(2)), 0.233 (Hp(1S)), and 0.033 (Hp1(1F)), which clearly indicated an increased frequency of Hp(2), a similar proportion of Hp(1S) and a diminished proportion of Hp(1F) in SLE patients compared with that in healthy controls. Preferential Hpalpha2 expression in SLE patients may contribute to some of the clinical manifestations of the disease such as hypergammaglobulinemia, systemic vasculitis, and cardiovascular disorders.