Summary
The high prevalence of free protein S deficiency in human immunodeficiency virus (HlV)-infected
patients is poorly understood. We studied 38 HIV seropositive patients. Free protein
S antigen values assayed using the polyethylene-glycol precipitation technique (PEG-fS)
were statistically lower in patients than in controls. These values using a specific
monoclonal antibody-based ELISA (MoAb-fS) and the values of protein S activity (S-act)
were not statistically different between patients and controls. C4b-binding protein
values were not different from control values. In patients, PEG-fS values were lower
than MoAb-fS values. Ten patients had a PEG-fS deficiency, 4 patients had a MoAb-fS
deficiency and 8 had a S-act deficiency. Protein S activity and MoAb-fS were lower
in clinical groups with poor prognosis and in patients with AIDS but PEG-fS was not.
A trend for reduced S-act/MoAb-fS ratios was observed in patients. PEG-fS was negatively
correlated with anticardiolipin antibody titers whereas MoAb-fS was not. The plasma
of PEG-fS deficient HIV-patients contained high amounts of flow cytometry detectable
microparticles which were depleted from plasma by PEG precipitation. The microparticles
were partly CD42b and CD4 positive but CD8 negative. These microparticles were labelled
by an anti free protein S monoclonal antibody. The observed differences between MoAb-fS
and PEG-fS values were correlated with the amount of detectable plasma microparticles,
just like the differences between MoAb-fS and S-act. Plasma microparticles correlated
with anticardiolipin antibody titers.
In summary, free protein S antigen in HIV infected patients is underestimated when
the PEG precipitation technique is used due to the presence of elevated levels of
microparticles that bind protein S. The activity of free protein S is also impaired
by high levels of microparticles. The prevalence of free protein S deficiency in HIV
positive patients is lower than previously published (4/38, -10%) and is correlated
with poor prognosis. By implication, use of a PEG precipitation technique might give
artefactually low free protein S antigen values in other patient groups if high numbers
of microparticles are present. In HIV patients, high titers of anticardiolipin antibodies
are associated with high concentrations of cell-derived plasma microparticles.