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Biomedical subjects

M A Kerr

Publications and source records attributed to M A Kerr.

At least 91 records · Page 5Linked to original sources
PubMed1987

Proteus mirabilis strains of diverse type have IgA protease activity.

A strain of Proteus mirabilis associated with chronic urinary tract infection was found to produce an EDTA-sensitive IgA protease that cleaved the IgA heavy chain into two fragments at sites different from those attacked by other microbial IgA1 proteases. Another 14 P. mirabilis strains of diverse type and from various clinical conditions also produced a similar IgA protease. This enzyme may be a virulence determinant of P. mirabilis.

Autoradiography↗
PubMed1987

Opsonization of yeast by human serum IgA anti-mannan antibodies and phagocytosis by human polymorphonuclear leucocytes.

The ability of sera from 72 patients with liver disease to opsonize yeast for phagocytosis by normal polymorphonuclear leucocytes has been studied. Seven showed defective opsonization. The opsonic activity of all but two sera was decreased markedly by heating at 56 degrees C for 1 h. When the two sera with heat stable opsonic activity were fractionated by gel filtration and by ion exchange chromatography, the activity copurified with IgA, not with IgG. The purified IgA, radiolabelled with 125I was shown to bind in a saturable manner to the yeast. Both sera had high levels of anti-yeast mannan IgA detected by an ELISA. In one case most of the anti-mannan activity was due to monomeric IgA, in the other it was dimeric. This was consistent with the observation of an apparent molecular weight of the opsonin of approximately 180 kD in one serum and 300-400 kD in the other.

Chromatography, Gel↗
PubMed1987

The mechanism of action of the factor in leprosy serum that inhibits the growth of mitogen-stimulated normal human lymphocytes.

A factor found in the serum of patients with leprosy that inhibits the growth of mitogen-stimulated normal peripheral blood lymphocytes has been studied. The inhibitor, previously identified as an IgG, has been shown to act by blocking the recruitment of lymphocytes into growth. It was not cytotoxic and did not inhibit the rate of growth of those lymphocytes that had been stimulated. The inhibitory activity was less potent if the serum was added after mitogen stimulation. The inhibitor, which could be absorbed by activated but not resting lymphocyte cultures, appeared to act by inhibition of an early event preceding the release of IL-2. The inhibition of mitogen stimulation was overcome by the addition of purified IL-2, although the inhibitor did not block the action of IL-2 on a long-term cultured IL-2-dependent cell line.

Adolescent↗
PubMed1987

Characterization of a factor in leprosy serum that inhibits the growth of mitogen-stimulated normal human lymphocytes.

A factor that inhibits the growth of mitogen-stimulated lymphocytes from normal donors has been detected in the sera of patients with chronic leprosy. The inhibitory activity was detected with similar frequency in patients with tuberculoid or lepromatous leprosy, although higher levels of activity were detected in the latter. The factor reduced the growth in volume of the lymphocytes in the first 24 hr after stimulation, the synthesis of RNA during the first 3 days of culture and the replication of DNA in 72-hr cultures. All the inhibitory activity co-purified with IgG on gel filtration, ammonium sulphate fractionation and ion exchange chromatography. The activity was stable to heating at 56 degrees but labile at 100 degrees and was absorbed from serum or from purified IgG preparations by staphylococcal protein A. On gel filtration of the sera on Sephadex G-200, none of the activity appeared in the void volume, indicating that it is not due to immune complexes. We conclude that the activity is due to an IgG antibody and suggest that it is an autoantibody since the sera inhibited the growth of all donor lymphocytes tested.

Adolescent↗
PubMed1986

Circulating immune complexes associated with decreased complement-mediated inhibition of immune precipitation in sera from patients with bacterial endocarditis.

The sera of patients with bacterial endocarditis frequently contain high levels of circulating immune complexes. In in vitro assays these sera have been shown to be deficient in the complement mediated inhibition of immune precipitation (immune complex solubilization) although C3 and C4 levels were often normal. The deficiency is due to the presence of a factor which also inhibits the ability of normal serum to solubilize immune complexes. This inhibitor is possibly rheumatoid factor which is frequently detected in endocarditis. Serial studies on 16 patients showed the levels of immune complexes, the ability to prevent immune precipitation and rheumatoid factor to correlate with disease activity. The similarity of the findings to those in rheumatoid arthritis are discussed.

Adult↗
PubMed1985

Expression in normal adult, fetal, and neoplastic tissues of a carbohydrate differentiation antigen recognised by antigranulocyte mouse monoclonal antibodies.

The distribution in paraffin fixed human tissues of a carbohydrate antigen defined by two monoclonal antibodies raised against human granulocytes has been studied by means of an immunoperoxidase technique. In addition to granulocytes, the antigen has been detected in adult tissues on identifiable cell types of the stomach, kidney, adrenal medulla, and brain and on the mucins of the gastrointestinal tract and other secretions. In fetal tissue, epithelial cells of the alimentary tract, lung, brain, and kidney express the antigen. Adenocarcinoma of the colon, stomach, breast, and lung are stained strongly, as are other types of lung cancer. The monoclonal antibodies give a staining pattern similar but not identical to other monoclonal antibodies raised against granulocytes or neoplastic cell lines which recognise the antigen 3-fucosyl N-acetyllactosamine. The use of antibodies against this oncofetal antigen in the study of differentiation and as tumour markers is discussed.

Adrenal Medulla↗
PubMed1985

Cleavage of the second component of complement by plasma proteases: implications in hereditary C1-inhibitor deficiency.

EDTA plasma from patients with hereditary angioedema (HAE), the genetic deficiency of C1-inhibitor, when incubated at 37 degrees produces a kinin-like activity which can induce contraction of oestrus rat uterus. The second component of complement (C2) has previously been suggested to be the source of this kinin-like activity, with the implication that C2-kinin is a normal product of complement activation. Our results show that purified human C2 is cleaved rapidly to C2a and C2b when added to HAE plasma, but not normal plasma or plasma from a danazol-treated HAE patient. However, the addition to HAE plasma of C2 at 20 X normal plasma concentration had no effect on the kinin activity generated on incubation at 37 degrees. In the presence of soya bean trypsin inhibitor, the rate of C2 cleavage and products were unaltered but no kinin activity was generated. C2 was cleaved by purified C1s to C2a and C2b. Incubation of C2 with trypsin resulted in cleavage to C2a and C2b followed by more extensive cleavage of both C2a and C2b. Kallikrein cleaved C2 to C2a and C2b but plasmin had no effect on C2. In no case was kinin activity generated. When C2 was cleaved by C1s to C2a and C2b then incubated with trypsin, kallikrein, or plasmin, no kinin activity was generated: only trypsin cleaved the C2 fragments further. The results suggest that C2 is not the source of the kinin-like activity generated in hereditary angioedema plasma.

Angioedema↗
PubMed1984

The effects of iodine and thiol-blocking reagents on complement component C2 and on the assembly of the classical-pathway C3 convertase.

I2 can react with complement component C2 in a two-stage process. In the first stage, a form of C2 with enhanced haemolytic activity is produced. This form of C2 is cleaved to C2a and C2b by C1s at the same rate as native C2. The enhanced C2 haemolytic activity correlates with the ability to form a stable fluid-phase C3 convertase on addition of the C2 to C4b and C1s. It reflects an increased affinity for C4b of C2a formed from I2-treated C2, although the affinity for C4b of I2-treated C2 itself is not markedly increased. The specific activity of C3 convertase formed from I2-treated C2 is the same as that formed from native C2. The second stage of the reaction with I2, which is favoured at high pH or in the presence of excess I2, inactivates C2 on production of a species that cannot be cleaved by C1s. The presence of a single free thiol group in C2, which is the site of modification by I2, was confirmed by titration with p-chloromercuribenzoate, iodoacetamide and 5,5'-dithiobis-(2-nitrobenzoic acid). A single thiol group is also present in Factor B, and the cysteine residue, like that in C2, requires denaturation of the protein before reaction with iodoacetamide and 5,5'-dithiobis-(2-nitrobenzoic acid) but not p-chloro- mercuribenzoate .

Chloromercuribenzoates↗
PubMed1983

The reaction of iodine and thiol-blocking reagents with human complement components C2 and factor B. Purification and N-terminal amino acid sequence of a peptide from C2a containing a free thiol group.

Human complement components C2 and Factor B each contain one free thiol group/molecule. Reaction with p-chloromercuribenzoate destroyed the haemolytic activity of C2 but had no effect on Factor B. Reaction of C2 with I2 gave a 16-fold enhancement of its haemolytic activity. The pH optimum for the reaction was 7.0. The I2 reacted at the thiol group in C2 with a stoicheiometry of 1 mol of I2/mol of C2. The product of the reaction was unaffected by millimolar concentrations of dithiothreitol; however, azide and cyanide were inhibitory. Reaction with azide did not result in re-expression of the thiol group. Mild oxidation of the thiol group with m-chloroperbenzoic acid did not enhance the haemolytic activity. The results suggest that reaction with I2 causes intramolecular covalent, but not disulphide, bond formation. I2 reacted with Factor B at the free thiol group without affecting the haemolytic activity. A CNBr-cleavage peptide from C2a (obtained by cleavage of C2 by subcomponent C1s) containing the free thiol group was isolated. Automated Edman degradation of the peptide showed that it was the N-terminal peptide of C2a. The free thiol group was identified at position 18.

Amino Acid Sequence↗
PubMed1983

The effect of C3 levels on yeast opsonization by normal and pathological sera: identification of a complement independent opsonin.

The ability of 150 normal and pathological sera to opsonize yeast for uptake by isolated human polymorphonuclear leucocytes has been studied. Phagocytosis was measured by an assay depending on electronic particle counting to measure yeast uptake and by a new fluorometric assay which is able to distinguish particle adherence from true phagocytosis. The opsonic activity of normal human serum was heat labile and depended markedly on C3 levels. The sera of 6% of healthy young adults (three from 45) and 8% of healthy donors aged 65-88 (four from 57) showed defective opsonization in spite of normal C3 and CH50 levels. Thirty-eight pathological sera with low C3 levels showed defective opsonization. However, three sera with low C3 levels showed apparently normal opsonic activity. The opsonin from two of these sera was characterized. It was heat stable, had apparent mol.wt of 400,000 and was active in serum free media. The opsonin was absorbed by immobilized Staphylococcus aureus and by gelatin-Sepharose, suggesting that it is related to fibronectin. Fibronectin from normal human sera prepared by affinity chromatography on gelatin-Sepharose was not opsonic in this system.

Adult↗
PubMed1982

The purification and properties of the second component of guinea-pig complement.

A method has been developed for the purification to homogeneity of guinea-pig complement component C2. Contrary to previous reports, guinea-pig C2 is a single polypeptide chain with apparent mol.wt. of 102000, the same as human C2. It is cleaved by C1s to yield fragments C2a (apparent molwt. 74000) and C2b (apparent mol.wt. 34000). The amino acid composition and N-terminal sequences of these fragments are similar to those of human C2a and C2b. Human and guinea-pig C2 show more extensive sequence homology to Factor B than previously identified. The known homology around the sites of cleavage by C1s and Factor D has now been extended by a stretch of ten identical or conservatively substituted residues. Sequence homology has now been identified at the N-terminal of C2b and Factor Ba. The properties of the classical-pathway C3 convertases assembled from human C4b, C1s and human or guinea-pig C2 have been compared. The rates of cleavage of human and guinea-pig C2 by C1s (and therefore the rates of assembly of the C3 convertases) are similar. The rate of decay of the activity of the C3 convertase formed from guinea-pig C2 is 10-fold lower than for human C2. This greater stability reflects a higher affinity of guinea-pig C2a for human C4b. The presence of C2b is not necessary for C3 convertase activity.

Amino Acid Sequence↗
PubMed1981

The separation of functionally distinct forms of the third component of human complement (C3).

Complement component C3 prepared by the method of Tack & Prahl [(1976) Biochemistry 15, 4513-4521] was found to contain the following trace contaminants: C3b, haemolytically inactive C3 with intact alpha- and beta-chains (C3u) and degraded C3 (apparent mol.wt. 140000) with an intact beta-chain but with a fragmented alpha-chain. The proportion of C3u in the C3 is increased on standing and by freezing and thawing. These contaminants could be separated from each other and from native C3 by chromatography on sulphated Sepharose. They have been characterized by their susceptibility to C3b inactivator in the presence of beta 1H, their ability to be cleaved by C3 convertase and their ability to form alternative-pathway C3 convertase in solution. Incubation of C3b or C3u with beta 1H and C3b inactivator resulted in cleavage of the C3 species; the alpha'-chain of C3b was cleaved to fragments of apparent mol.wts. 67000 and 43000, the alpha-chain of C3u was cleaved to fragments of apparent mol.wt. 75000 and 43000. Native C3 and degraded C3 were unaffected by incubation with beta 1H and C3b inactivator. C3u, unlike C3, was not cleaved to C3b by the classical- or alternative-pathway C3 convertase in solution. When C3b or C3 was incubated with factors B and D, forming C3 convertase, the initial rate of factor-B cleavage was several order of magnitude lower in the presence of C3 than in the presence of C3b. The slow rate observed for C3 could be decreased by preincubation with beta 1H and C3b inactivator or by rechromatography of the C3. The degraded C3 did not support factor-B cleavage by factor D.

Chromatography, Affinity↗
PubMed1981

Human factor B.

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Amino Acids↗
PubMed1980

The human complement system: assembly of the classical pathway C3 convertase.

The assembly of the classical pathway C3 convertase in the fluid phase has been studied. The enzyme is assembled from C2 and C4 on cleavage of these proteins by C1s. Once assembled, the enzyme activity decays rapidly. Kinetic evidence has been obtained that this decay is even more rapid than previously suggested (kdecay is 2.0 min-1 at 37 degrees C). As a result, optimal C3 convertase activity is only observed with high C1s levels, which result in rapid rates of cleavage of C2 and increased rates of formation of the C3 convertase. Using high concentrations of C1s at lower temperatures (22 degrees C) in the presence of excess substrate we have demonstrated kinetically that the enzyme comprises an equimolar complex of C4b and cleaved C2. We have obtained direct evidence from gel-filtration experiments for the role of C2a as the catalytic subunit of the enzyme. C2b appears to mediate the interaction between C4 (or C4b) and C2 at pH 8.5 and at low ionic strength where the interactions can easily be detected. It may therefore be important in the assembly of the enzyme, though it is not involved in the catalytic activity. The decay of the C3 convertase reflects the release of C2a from the C4b x (C2b) x C2a complex, and the stabilizing effect of iodine on the C3 convertase is therefore apparently one of stabilizing the C4b-C2z interaction, which is otherwise weak. C1s is not a part of the C3 convertase enzyme.

Chemical Phenomena↗