Biomedical subjects

L A Worfolk

Publications and source records attributed to L A Worfolk.

4 recordsLinked to original sources

PubMed1996

Monocyte/macrophage regulation of coagulant events.

Monocytes/macrophages actively regulate both the assembly and function, as well as the substrate specificity, of various coagulation enzymes at their membrane surface. Regulation is effected through a variety of mechanisms, not limited to, but including the expression of receptors (or 'binding sites') for the various protein constituents of the complexes, the expression of different receptors which may alter the function of the protease, and the expression of membrane proteases which may affect protein cofactor function. Monocyte stimulation with various agonists modulates many of these responses as does their adherence to and differentiation on various substrates.

Blood Coagulation↗

PubMed1993

Procoagulant activities expressed by peripheral blood mononuclear cells.

These combined data support the concept that the procoagulant response elicited by mononuclear cells, particularly monocytes, is accomplished through regulated binding site-mediated (or perhaps "receptor"-mediated) assembly of proteolytic activities at their membrane surface. Because the work of several laboratories indicate that the monocytes provide the appropriate membrane surface for the assembly and function of all the coagulation complexes required for thrombin production in vivo, monocytes may provide a unique opportunity to investigate how coagulant reactions are regulated on cell surfaces through both receptor-mediated events as well as by channeling a product of one reaction to serve as a mediator of a second reaction.

Cell Separation↗

PubMed1992

Factor Xa interacts with two sites on monocytes with different functional activities.

Studies were performed to elucidate the functional significance of factor Xa interactions at the monocyte membrane in the presence and absence of factor Va, with respect to prothrombin and factor IX cleavage. Factor Xa-catalyzed prothrombin activation at the monocyte surface was absolutely dependent on the addition of factor Va, indicating that thrombin was generated solely by a membrane-bound complex of factors Va and Xa. In contrast, in the absence of added factor Va, factor Xa bound to monocytes catalyzed the cleavage of factor IX to the nonenzymatic intermediate factor IX alpha through a reaction that was dependent on both monocyte and factor Xa concentration. At limiting factor Xa concentration, added factor Va inhibited the factor Xa-catalyzed cleavage of factor IX, suggesting that a monocyte-bound complex of factors Va and Xa did not recognize factor IX as a substrate. These combined data suggest that factor Xa interacts with the monocyte through two sites which can be distinguished by their requirement for added factor Va and their expression of different functional activities. Both functional sites could be distinguished also by their differential susceptibility to inhibition by a monoclonal antibody directed against the light chain of factor Va (alpha-HFV1). At the monocyte surface, the factor Va/Xa-catalyzed activation of prothrombin was maximally inhibited with 0.25 mumol/L alpha-HFV1, whereas 1.0 mumol/L alpha-HFV1 was required to effect 50% inhibition of the factor Xa-catalyzed cleavage of factor IX. The ability of factor Va to modulate factor Xa substrate specificity was investigated further. Factor Xa bound to thrombin-activated platelets either through platelet-released factor Va or added factor Va did not cleave factor IX. Consistent with this result, a plasma concentration of factor IX had no effect on thrombin generation catalyzed by a platelet-bound complex of factors Va and Xa. In marked contrast, factor Xa bound to phospholipid vesicles either independently or in complex with factor Va catalyzed factor IX cleavage with equal efficiency. These combined data indicate that factor Va bound to cell surfaces modulates factor Xa substrate specificity, whereas no discriminatory effect is conferred by factor Va bound to phospholipid vesicles. Thus, by providing two distinct sites at its membrane surface, the monocyte modulates factor Xa binding and the functional activity expressed by the bound enzyme, depending on the availability of factor Va.

Antibodies, Monoclonal↗

PubMed1991

The detection of platelet alloantibodies by flow cytometry.

A flow cytometric procedure was investigated for its ability to detect antibodies directed against blood group A, HLA, and PlA1 (HPA-1a) antigens. When type O sera were tested against platelets from blood group A donors, only 9 of 14 positive reactions were observed. Furthermore, the expression of blood group A varied more than 100-fold on platelets derived from individual donors. When anti-HLA-A2 and -B7 were evaluated, 11 of 11 individuals with HLA-A2 and -B7 antigens reacted. In contrast, when platelets from donors whose HLA antigens included HLA-B8 or -B12 were tested with anti-HLA-B8 or -HLA-B12, respectively, positive reactions were observed in only 3 of 7 instances, despite the fact that the lymphocytes reacted strongly. Platelets from 10 HLA-A2-positive donors, which had been stored for up to 20 months at -70 degrees C, were studied. In all cases, frozen-stored platelets reacted well with an anti-HLA-A2. Limited testing with an anti-PlA1 (anti-HPA-1a) showed equal reactivity with fresh and frozen platelets. Finally, the method was compared to a visual immunofluorescence assay using sera from patients who were refractory to platelet transfusions. The results agreed in 30 of 37 comparisons, and most discrepancies were resolved in favor of flow cytometry. It is concluded that flow cytometry is useful for detecting platelet alloantibodies and possibly for prospective platelet crossmatching, as HLA- and platelet-specific antibodies can be identified by using platelets stored frozen for several months.

ABO Blood-Group System↗