Detection, by an enzyme linked immunoadsorbant assay (ELISA), of IgM, IgG and IgA rheumatoid factors in patients with essential mixed cryoglobulinemia.

In order to investigate on some yet unclear aspects of the relationship between Rheumatoid Factor (RF) activity, cryoprecipitation and clinical features of Essential Mixed Cryoglobulinemia (EMC), we determined, by an ELISA technique, the IgM, IgG and IgA RF in 16 patients with EMC, 16 patients affected with seropositive Rheumatoid Arthritis (AR), taken as a reference, and 16 young, normal controls. For IgM RF a high rate of incidence of positive samples (11/16 = 69%) from the EMC group was found, with mean values significantly higher than controls (p less than 0.001) and quite similar to those of the RA group. The ELISA assay was performed at room temperature (RT) and at 37 degrees C, and only a slight increase of adsorbance values in the latter condition was observed. On the contrary, temperature revealed to be a critical experimental condition for the detection of IgG RF. In fact at 37 degrees C the mean values of EMC patients were similar to those of RA and control groups, while at RT a marked increase of adsorbance values was observed, in spite of the inactivation of IgMRF due to the preliminary pepsin digestion of the samples. More interesting are our results concerning IgA RF. In fact a high incidence of overnormal values (9/16 = 56.2%) were found in the EMC group, similar to those of RA patients, with mean values which significantly differ from the normal subjects (p less than 0.01). No relevant differences derived from the temperature at which the test was carried out. The relationship between IgA RF and clinical course of EMC seems to be a very stimulating aim for further investigations.