Search

Madam P, 77 years old, consulted in the hemostasis department after a coagulation anomaly was discovered during her preoperative test for a total hip prosthesis. After confirmation of a persistent and increased aPTT, additional tests were performed and showed the presence of antiphospholipid antibodies. Factor VIII level could be corrected after the plasma dilution to 1/40(th). But successive dilutions were not enough to obtain a correct factor IX (FIX) and factor XI (FXI) level. FIX level was obtained by chromogenic method in order to avoid the interferences caused by the antibodies. Finally, despite the change of reagents and dilutions up to 1/160(th), the FXI level couldn't be determined. Despite these results and those of the thrombin generation assay, the surgery was successfully done without specific treatment thanks to the absence of hemorrhagic history. This observation highlights the diagnostic and monitoring difficulties for uncommon clotting factor deficit. The development of interference free test could increase the support for these patients.

In this paper, we report an inhibitor antibody to factor XI (FXI) in a woman with severe inherited FXI deficiency, induced by FXI present in an Rh immune globulin preparation. The patient is homozygous for the Glu117Stop mutation, associated with a FXI level of less than 1 U/dL. Unlike all previously described patients with severe FXI deficiency and an inhibitor, the patient had never been exposed to blood products. Following 3 injections of Rh immune globulin during pregnancy, she developed an inhibitor to FXI (8 Bethesda units) that was shown to bind specifically to FXI and inhibit factor IX cleavage by purified FXIa. The administered Rh immune globulin and 2 other similar products were shown to contain FXI. Clinicians should be aware of the potential for immunization of severely FXI-deficient patients by FXI present in Rh immune globulin preparations.

Factor XI deficiency, an injury-related bleeding disorder, is rare worldwide but common in Jews in whom 2 mutations, Glu117Stop (type II) and Phe283Leu (type III), prevail. Mean factor XI activities in homozygotes for Glu117Stop and for Phe283Leu are 1 and 10 U/dL, respectively. Inhibitors to factor XI in patients with severe factor XI deficiency have been reported in a small number of instances. This study was undertaken to determine the prevalence of acquired inhibitors against factor XI in patients with severe factor XI deficiency, discern whether these inhibitors are related to specific mutations, and characterize their activity. Clinical information was obtained from unrelated patients with severe factor XI deficiency, and blood was analyzed for factor XI activity, inhibitor to factor XI, and causative mutations. Immunoglobulin G purified from patients with an inhibitory activity was tested for binding to factor XI, effects on activation of factor XI by factor XIIa and thrombin, and activation of factor IX by exogenous factor XIa. Of 118 Israeli patients, 7 had an inhibitor; all belonged to a subgroup of 21 homozygotes for Glu117Stop who had a history of plasma replacement therapy. Three additional patients with inhibitors from the United Kingdom and the United States also had this genotype and were exposed to plasma. The inhibitors affected factor XI activation by thrombin or factor XIIa, and activation of factor IX by factor XIa. The results imply that patients with a very low factor XI level are susceptible to development of an inhibitor following plasma replacement.

Inhibitors against factor XI (FXI) have been frequently described in patients who acquired inhibitors (due to auto-immune disorders, malignancies or infections), but less often in those with a congenital deficiency of this factor, who had received plasma infusions. The present report concerns one such inhibitor found in the plasma of a patient with chronic myelomonocytic leukaemia and infected by B19 parvovirus, who was neither a heterozygote nor a homozygote for FXI deficiency, and who had no bleeding tendency despite a very low FXI level. Taking this case into account, we discuss and present the clinical and biological features of acquired FXI deficiency caused by an inhibitor.

Cattle, homozygous for the genetic disorder of factor XI (FXI) deficiency, exhibit less than 2% of normal plasma FXI activity, display an increased bleeding tendency and are more prone to infectious diseases. FXI is one of the protein components of the contact activation system of coagulation that assembles on the surface of circulating neutrophils. Because of the central role of neutrophils in inflammation, the in vitro responses of neutrophils from normal and FXI deficient cattle were compared. Neutrophil degranulation was evaluated by measuring the release of myeloperoxidase and alkaline phosphatase, and the respiratory burst was evaluated by determining superoxide anion production. Neutrophils from FXI deficient animals exhibited a significant increase (P < 0.05) in the spontaneous release of granule contents compared to the cells from normal cattle. Following stimulation with C5a complement derived from normal serum, the neutrophils from the FXI deficient animals exhibited a greater increase (P < 0.05) in both alkaline phosphatase release and superoxide production. In these neutrophils, following stimulation with C3b complement from normal serum, the relative increase in myeloperoxidase release compared to the unstimulated neutrophils was lower than that observed in the neutrophils from normal animals. There was minimal superoxide production in unactivated neutrophils from either normal or FXI deficient cattle and the response to phorbol ester stimulation was similar in both groups of animals. The C5a complement from FXI deficient serum was more effective (P < 0.05) in stimulating alkaline phosphatase release and superoxide production in normal neutrophils than the equivalent fraction from FXI deficient serum while the C3b complement from the FXI deficient serum was less effective than the normal serum fraction at inducing myeloperoxidase release from normal neutrophils. The results indicate that the differences in the in vitro neutrophil function are likely related to a variation in the function of the contact activation system on the neutrophil surface between normal and FXI deficient animals.

The results of studies in a patient with congenital deficiency of Factor XI who developed an inhibitor are presented. The patient presented with a severe, apparently spontaneous bleed into the thigh, which progressed despite infusion of fresh frozen plasma, but which responded promptly to activated prothrombin complex. During therapy with plasma his clotting time and Factor XI level were unresponsive and a Factor XI inhibitor titer of 6,000 U/ml was attained. The inhibitor was isolated and found to be polyclonal immunoglobulin G (IgG), predominantly of subclass 4. The specificity of the antibodies for Factor XI was shown by the ability of isolated inhibitor bound to polyacrylamide beads to remove Factor XI selectively from normal plasma. The binding of (125)I-labeled factor XI to the inhibitor was studied and an affinity constant of 1.65 x 10(10) liter/mol was found. Complexing of the antibodies with Factor XI was shown to block multiple activities of the clotting factor. Factor XI complexed with antibody did not bind to high molecular weight kininogen or undergo activation and cleavage by two-chain Factor XII. The complex of activated Factor XI with inhibitor prevented the cleavage and activation of Factor IX. Hence the inhibitor appears to act by binding to multiple sites on the Factor XI molecule and preventing its interaction with other molecules. Clinically these interactions of the inhibitor with Factor XI result in a state of severe Factor XI deficiency. The clinical circumstances of the case, with severe hemorrhage refractory to plasma infusion but readily responsive to an alternate clot-promoting agent, suggest that a defect of intrinsic system activation was critical, supporting the inference that Factor XI does participate in normal hemostasis. The clinical course of this patient, who has only had two documented hemorrhages in the presence of the inhibitor, is not as severe as that of patients with severe Factor VIII or IX deficiency. This suggests that physiologic activation of Factors XI and IX does not occur exclusively in series because deficiency of factors XII, XI, VIII, and IX should then have similar hemostatic consequences. We propose that independent mechanisms for bypass of Factors XII and XI are important in physiologic activation of coagulation.

A relatively potent antiserum against highly purified, unactivated human factor XI antigen was raised in a rabbit. This antiserum, after concentration, neutralized 50% of the factor XI clotting activity of a standard normal plasma at an antiserum dilution of 1/900. The antiserum was used in a neutralization-inhibition assay to study the relation between factor XI clotting activity and factor XI antigen in plasma from ten unrelated patients with homozygous factor XI deficiency and from 12 heterozygous family members of these patients. No evidence of factor XI antigen significantly in excess of factor XI activity was found in either group. All data to date have been consistent with the hypothesis that hereditary factor XI deficiency represents a genetic disorder resulting from the absence of factor XI molecule. Severity of bleeding in factor XI deficiency could not be correlated with the level of factor XI activity or factor XI antigen.

A homozygous factor XI-deficient girl, who appeared to be positive for cross-reacting material (CRM+) was studied for clarification. Factor XI antigen (F XI:Ag) was measured by radial immunodiffusion using monospecific, heterologous anti-factor XI antibodies. Factor XI coagulant activity (F XI:C) was determined in a modified activated partial thromboplastin time (APTT) test. The ratio of F XI:C to F XI:Ag was 0.04 for the proposita, as compared with 0.7 to 0.74 in the other family members. In contrast, 12 normal individuals had ratios of F XI:C to F XI:Ag of 1.04 +/- 0.15. F XI esterolytic activity was clearly higher than F XI:C in the proband, but not in her relatives. Immunoblotting studies demonstrated F XI CRM in the patient's plasma. Chromatography on diethylaminoethanol (DEAE)-Sephadex at pH 8.4 led to an almost complete removal of F XI from the plasma. The defective F XI was not bound to a negatively charged kaolin surface due to an abnormal interaction with high-mol-wt kininogen (HMWK).

Antibodies against the human T-leukemia virus III (HTLV III) were detected by immunofluorescence in the sera of 17 out of 48 hemophiliacs (35.4%) without AIDS or ARC, frozen in 1983-84. Immunological data collected at that time were re-evaluated by separating HTLV III-positive and negative subjects. HTLV III positive patients had significantly reduced OKT4 cells (both in %: 26.1 +/- 10.9 vs 41.2 +/- 15.2; P less than 0.01; and in absolute numbers: 469 +/- 291 vs 1,038 +/- 541; P less than 0.005) and OKT3 lymphocytes (in absolute numbers: 1,234 +/- 550 vs 2,050 +/- 1,067; P less than 0.01). Subpopulations identified by other monoclonal reagents (OKT8, Leu 7, OKM1, anti-Tac) showed no significant differences between the two groups. Patients subsequently found to be seropositive had significantly more frequent anergy to skin tests to recall antigens and often an impairment of in vitro response to phytohemagglutinin A. Despite these relevant defects of some tests of cell-mediated immunity, in HTLV III-positive cases no clinical progression toward AIDS-related complex was observed in a mean period of follow-up of more than 1.5 years.