The mechanism of loss of CR1 during maturation of erythrocytes is different between factor I deficient patients and healthy donors.

During the in vivo maturation of erythrocytes, the number of CR1 per cell decreases by approximately two-thirds in 30 days. The CR1 loss is enhanced in several diseases such as SLE, AIDS, and particularly in factor I deficiency. Microvesicles enriched in CR1 and DAF are released from erythrocytes matured in vitro, leading to the same loss of both molecules. When comparing reticulocytes and erythrocytes, CR1 and DAF were lost similarly in 15 normal individuals, suggesting that vesiculation may be at the origin of CR1 loss in vivo. However, the enhanced loss of CR1 in 3 patients with factor I deficiency was contrasted with a normal loss of DAF, raising the possibility that, in this pathological condition, CR1 might be proteolytically cleaved, leaving small CR1 fragments on the erythrocytes. To answer this question, a rabbit polyclonal antibody was raised against the cytoplasmic (tail) domain of CR1, which recognised specifically CR1 of erythrocytes and urinary vesicles on Western blots. However, no CR1 fragments could be detected on erythrocytes of the factor I deficient patients although this antibody was able to recognise CR1 fragments after treatment of normal erythrocytes or urinary vesicles with elastase. These data suggest that cell surface domains rich in CR1, but not in DAF, are specifically lost in factor I deficiency.

Association of a pool of HIV-1 with erythrocytes in vivo: a cohort study.

BACKGROUND: Treatment of HIV-1-infected individuals with antiretrovirals can result in sustained suppression of plasma viral RNA at concentrations below the detection limit of available assays. However, continuing virus replication has been detected in patients with viral RNA in plasma suppressed for months to years, and many cell types are known to act as reservoirs or carriers for the virus. In vitro, erythrocytes bind HIV-1 immune complexes, so we tested for a circulating pool of HIV-1 associated with erythrocytes in people with HIV-1 infection. METHODS: We investigated 82 chronically HIV-1-infected individuals. Plasma, white cells, and erythrocytes were tested for HIV-1 RNA by RT-PCR. FINDINGS: Erythrocyte-associated HIV-1 RNA was detected in 80 of 82 individuals. In 23, plasma HIV-1 RNA had been undetectable (<20 copies/mL) for up to 32 months; in corresponding erythrocyte samples, there were up to 82878 HIV-1 RNA copies per mL whole blood. HIV-1 associated with erythrocytes in vivo was shown to be infectious. Within the subgroup of patients with undetectable plasma viral load, higher numbers of HIV-1 associated with erythrocytes were correlated with a history of advanced clinical stages of HIV-1 infection (p=0.014). INTERPRETATION: A pool of HIV-1 is associated with erythrocytes even after long-term suppression of viral RNA in plasma. This finding is direct evidence for continuing virus replication or release in these individuals. Quantification of this viral pool may help to judge suppression of HIV-1 replication in individuals with undetectable plasma HIV-1 RNA.

Distinct forms of DAF in urine and blood.

DAF is a GPI-anchored protein expressed on all blood cells and most other cell types. This complement regulatory protein functions intrinsically in cell membranes to protect host cells from autologous complement attack. A soluble form is found in body fluids. In human urine, two forms of DAF have been described. Here we report that these two forms correspond to soluble DAF and to DAF bound onto urinary vesicles. With a newly established, highly sensitive ELISA, the proportion of these two forms could be quantified in healthy individuals and patients having renal disorders. This ELISA allowed us to measure DAF on blood cells and also in plasma. In contrast to urine, human plasma contained only soluble DAF when the plasma was thoroughly depleted of platelets. The concentration of soluble DAF in human serum was always lower than in the corresponding plasma, suggesting that this form might adhere to the clot during the coagulation process.