[Selective binding in vitro of a modified form of the C3 component of complement to human erythrocytes]. / Fixation sélective in vitro d'une forme modifiée du composant C3 du complément sur des érythrocytes humains.

C3 was bound to human erythrocytes from autologous plasma or from serum brought to low ionic strength (mu less than or equal to 0.03) and pH between 4.0 and 5.0, then subsequently incubated with erythrocytes (50/1, v/v) for 20 min at 0 degree C. This capacity was preserved up to 72 h by prolonged incubation at 20, 25 or 37 degrees C, whereas it was quickly lost by incubation at 0 degree C. C3 binding did not require complement activation and was not observed with neuraminidase-treated erythrocytes. Crossed immunoelectrophoretic analysis of the pretreated serum or plasma revealed that a fraction having more cathodal migration than that of native C3 was generated upon incubation in the above-mentioned conditions. This fraction appeared able to selectively bind to the erythrocytes. Cell-bound C3 reacted positively to antisera against C3a, C3c, C3d or native C3; they rosetted positively with EAC3b, clearly showing that this C3 binding was not dependent on the proteolysis of C3 and that it concerned the acceptor sites on the cells, since C3b receptors were free. The functional significance of this C3 binding was also investigated: EC3 were not able to lyse through the alternative pathway, whereas lysis clearly increased when C3 was found to AET-treated erythrocytes. This finding, together with the modulation in the capacity of EC3 or E(AET)C3 to form an alternative pathway convertase by antibodies to C3c or C3d, strongly suggests a contribution of bound C3 to such a convertase. In contrast to "C3b-like" C3, this modified C3 was able to bind to acceptor sites on erythrocytes but, like the former, it retained the capacity to form an alternative pathway convertase. In this light, it may represent an intermediate between C3 and "C3b-like" C3.

[Serum immune complexes in rheumatoid arthritis (a study of 100 cases). Comparison of the results obtained by four different detection techniques]. / Les complexes immuns dans le sérum au cours de la polyarthrite rhumatoïde. A propos de 100 cas. Comparaison des résultats obtenus par quatre techniques de détection différentes.

The detection of serum immune complexes in cases of rheumatoid arthritis (RA) was performed using four different detection techniques: cryoglobuline (CG), the polyethylene glycol C1q test (PEGC1q), the 125I labelled C1q test (C1qBA) and the detection of anticomplement power (ACP). CG, PEGC1q, and C1qBA are more often positive in cases of sero-positive RA than in sero-negative RA (p less than 0,001 for each test). There are significant and relatively concordant correlations between the positivity of these three tests and certain clinical and laboratory parameters in particular, the level of rheumatoid factor (p less than 0,001) and the presence of extra-articular manifestations. When ACP is found in cases of RA of recent onset, it is associated, in sero-positive cases of RA, with the presence of immune complexes and a more severe form of the disease.