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Biomedical subjects

T Browning

Publications and source records attributed to T Browning.

6 recordsLinked to original sources
PubMed1995

Aminopeptidase-N (CD13; gp 150): contrasting patterns of enzymatic activity in blood from patients with myeloid or lymphoid leukemia.

We have investigated the compartmentalization of aminopeptidase-N-like activity in various blood fractions obtained from patients with acute lymphoid (ALL) or myeloid (AML) leukemia. The primary difference appears not to be the absolute level of overall activity, but rather the relative proportions of the different forms of activity detected. Thus, despite similar levels of total aminopeptidase-N-like activity detected in cells from different leukemic groups, true aminopeptidase-N/CD13 activity was only detected in cells derived from AML patients. Even in these patients, however, most of the detected aminopeptidase-N-like activity ( > 80%) could not be attributed to aminopeptidase-N/CD13. In marked contrast, plasma from leukemic patients also contained substantial total aminopeptidase-N-like activity, of which (irrespective of leukemic group) most could be attributed to aminopeptidase-N/CD13. Whilst slightly higher levels of total activity were obtained in plasma from AML patients compared to ALL patients, there was no difference in the relative proportion attributable to aminopeptidase-N/CD13 (approximately 80% of total aminopeptidase-N-like activity). Evaluation of total aminopeptidase-N-like activity present in whole blood gave differential patterns, and whilst only a proportion (20-40% of total aminopeptidase-N-like activity) could be attributed to true aminopeptidase-N/CD13, blood from patients with CD13+ AML showed the greatest activity so attributable. In total, our results outline the complexities of peptidase activities present within blood of leukemic individuals, and may, in part, explain the variability of previous studies attempting to associate prognostic features with phenotypic expression of CD13.

Antibodies, Blocking↗
PubMed1995

Functional and phenotypic upregulation of CD13/aminopeptidase-N on precursor-B acute lymphoblastic leukemia after in vitro stimulation.

Acute lymphoblastic leukemia (ALL) cells of precursor-B type were assessed for expression of the cell surface peptidase CD13 (aminopeptidase-N) after 72 hours' culture in 10% B cell growth factor (BCGF), TPA, or medium alone. CD13 was analyzed phenotypically using a specific monoclonal antibody (mAb) by flow cytometry, and also with a spectrophotometric enzyme assay to measure the cleavage of specific peptide substrates. CD13 antigen was induced in all 10 cases of precursor-B ALL after culture with BCGF, with weaker expression seen in cells incubated with TPA or in medium alone. Aminopeptidase-N-like enzymatic activity was also demonstrated in cultured cells, particularly after BCGF exposure. Using the mAb WM-15, which specifically inhibits aminopeptidase-N function, we demonstrated that induction of true aminopeptidase-N activity was largely restricted to BCGF-treated cells, in which approximately 20% of total aminopeptidase activity was due to aminopeptidase-N. Phenotypic expression of the peptidase CD10 (neutral endopeptidase) was not altered on cultured cells. These findings indicate that CD13 expression can be selectively upregulated on ALL cells in response to proliferative stimuli. This peptidase, in cooperation with CD10 and perhaps other surface enzymes, may act to regulate the concentration of molecules at the cell surface which influence the growth of precursor-B ALL cells.

Adolescent↗
PubMed1993

The hepatobiliary disease marker serum alanine aminopeptidase predominantly comprises an isoform of the haematological myeloid differentiation antigen and leukaemia marker CD-13/gp150.

In clinical chemistry, determination of serum alanine aminopeptidase (AAP) levels has been found to be useful for detecting or confirming biliary obstructions from either intra- or extra-hepatic disorders. In haematology, 'gp150' is a surface-expressed protein molecule, recognised by monoclonal antibodies belonging to the so-called 'Cluster of Differentiation' (CD-) 13, which has independently been found to be a useful marker of myeloid leukaemia in addition to providing potential prognostic value. The current report links these two independent research streams and provides evidence that the hepatobiliary disease marker, serum AAP, predominantly comprises a circulating isoform of 'gp150'. Thus, a (CD-13) monoclonal antibody raised to, and specifically reactive with, cell surface myeloid 'gp150' is able to specifically and almost completely block serum (or plasma) AAP activity otherwise observed in its absence. This holds true for serum (or plasma) derived both from normal individuals or from patients suffering hepatic dysfunction, with or without associated biliary obstruction. In the case of patients with obstructive jaundice, raised levels of AAP are observed, which fall to near normal levels following preincubation with this monoclonal antibody. In addition, data are presented to support the view of varying isoforms of AAP within flowing blood. Finally, preliminary data is provided on AAP activity in cases of leukaemia. These studies should thus prove of use to clinical laboratories investigating the involvement of AAP activity in various pathological processes.

Aminopeptidases↗
PubMed1993

CD13 (GP150; aminopeptidase-N): predominant functional activity in blood is localized to plasma and is not cell-surface associated.

This study is the first to report the presence of CD13/glycoprotein 150 (GP150)/aminopeptidase-N activity in cell-free plasma. We have determined that aminopeptidase-N in plasma provides, quantitatively, aminopeptidase-N's predominant functional activity within flowing blood. Thus, while aminopeptidase-N activity observed in whole blood can be partly, but significantly, blocked by the CD13 monoclonal antibody (MAB) WM15, the magnitude of such inhibition is low (< 25%) and similar to that observed using washed cell fractions selectively enriched for neutrophils (30.6% inhibition) or monocytes (21.8% inhibition). Plasma, free of cell components, possesses substantial aminopeptidase-N activity that is largely inhibitable (> 70%) by WM15. Blood collected into heparin or citrate yields similar data, while blood collected into EDTA gives rise to reduced CD13/aminopeptidase-N activity, consistent with inhibition of the known heavy-metal ion association necessary for proper functioning of this molecule. Although monocyte- and granulocyte-enriched cell fractions possess aminopeptidase-N activity significantly inhibitable by CD13 antibodies, lymphocyte-enriched cell fractions also possess aminopeptidase-N-like activity; however, in the latter case, this activity is not inhibitable by CD13 antibodies. Immunoaffinity isolation of plasma aminopeptidase-N has also been carried out; further characterization using functional studies and sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) electrophoresis indicates that CD13 MABs can completely clear plasma of aminopeptidase-N activity and that the purified protein has similar electrophoretic characteristics to cell-derived material. These data, therefore, provide evidence for the presence within blood both of a soluble (that is, non-cell-associated) form of CD13/GP150/aminopeptidase-N localizable to plasma and of cell-associated, aminopeptidase-N-like proteins other than CD13/GP150. These findings have significant implications for our understanding of the many functions of this molecule in blood.

Aminopeptidases↗