The lupus anticoagulant. High incidence of 'negative' mixing studies in a human immunodeficiency virus-positive population.

We identified 100 patients (51 males and 49 females) as having the lupus anticoagulant. The following diagnoses were found in the patient population: human immunodeficiency virus positivity, 20%; systemic lupus erythematosus, 10%; prolonged preoperative activated partial thromboplastin time (APTT), 10%; procainamide hydrochloride-induced inhibitor, 9%; deep vein thrombosis, 6%; seizure disorders/epilepsy, 5%; and miscellaneous conditions, 40%. Identification was based on a prolonged APTT (> 40 seconds) that normalized with increased phospholipid concentrations and/or a prolonged Russell viper venom clotting time patient-control ratio of 1.20 or greater. In 68 cases (group 1), patient plasma prolonged the APTT of normal plasma in a 1:1 mixing study. However, in 32 cases (group 2), no such prolongation was observed. There was a significant difference between presenting APTTs in patients from group 1 (mean +/- SD, 58.29 +/- 13.30 seconds) compared with that in group 2 (mean +/- SD, 47.93 +/- 5.09 seconds). Furthermore, 66% of group 1 patients had elevated anticardiolipin antibody titers compared with only 41% in group 2. Of the 32 patients in group 2, 16 (50%) were positive for human immunodeficiency virus. We concluded that the investigation of a lupus anticoagulant should not be abandoned because patient plasma does not prolong the APTT of normal plasma in a mixing study, especially in a human immunodeficiency virus-positive population.

Cryopreservable neutrophil surrogates. Stored cytoplasts from human polymorphonuclear leukocytes retain chemotactic, phagocytic, and microbicidal function.

Cryopreservation of polymorphonuclear leukocytes (PMN) has largely failed, probably because of their rich content of granular (lysosomal) enzymes. We have been developing granule-poor cytoplasts (anucleate fragments) from PMN which retain motile functions of the parent cell. The two types studied here were induced either by brief heating on surfaces (cytokineplasts) or by discontinuous gradient centrifugation (Ficoll) without heat or drugs (U-cytoplasts). Freshly made, these cytoplasts respond chemotactically to formyl peptide (fMet-Leu-Phe), and they take up and kill roughly half as many Staphylococcus aureus as their (larger, granular) parent PMN. Unlike their parent cells, after cryopreservation both cytoplasts remain chemotactic, and in matched experiments they take up and kill staphylococci with undiminished avidity. These findings are the first indications that PMN cytoplasts suitable for clinical use may be feasible.