Two young girls with type IIa homozygotic familial hypercholesterolemia were treated by plasma exchange to reduce circulating cholesterol levels, values prior to treatment being abnormally elevated (greater than 10 mmol/l). Simultaneous determination of membrane fluidity (by fluorescence polarization) of erythrocytes and lymphocytes showed marked decreases due principally to an increase in the intramembrane cholesterol/phospholipid ratio. Values after treatment showed a tendency to return to physiologic levels without, however, attaining normal values. In vitro studies of cholesterol incorporation in these membranes demonstrated the primordial role of cholesterol in these processes of membrane rigidity, and their reversibility. It is suggested that certain physical membranal properties could provide a useful index to assess need for more or less frequent plasma exchanges.

Neonatal alloimmune thrombocytopenia (NAITP) is primarily due to a foeto-maternal incompatibility of a specific platelet alloantigen. When the PLA1 antigen [1] is involved, its incidence has been recently evaluated to 1/3000 births [2]. The PLA1 antigen has been located on the platelet membrane glycoprotein Ilia [3]. This glycoprotein is mainly involved in the platelet aggregation system. The Glanzmann thrombasthenia is due to a lack of this protein [4] and in this disease patients can have severe hemorrhages. In vitro it was shown that the platelets were unable to adhere after activation [5]. Von dem Borne et al. [6] have shown that the antibody anti-PLA1 interacts in the normal platelet aggregation process. So it was of interest to study the effect of the interaction of such an antibody on the membrane platelet fluidity and order. For this purpose fluorescence polarization was used. The method allows a submacroscopic level of investigation in membrane fluidity studies which is directly correlated with physicological events [7].

The authors report on the case of a 12 year old girl, presenting with severe systemic lupus erythematosus. Skin, joints and kidney were involved. The treatment associated steroids, plasma exchanges and cyclophosphamide. Remission has been obtained and remains one year later.