Idiotypic interactions in type II mixed cryoglobulins.

An analysis of interactions between immunoglobulin molecules within cryoglobulins has been carried out in 18 patients with type II mixed cryoglobulinemia. In this series, there was a prevalence of VH I and VK I variable regions subgroups in the monoclonal IgM component. Our analysis of the IgG component indicated a particular selection of IgG molecules during cryoprecipitation. There was a prevalence of IgG3 and of the VH I subgroup and the isoelectrofocusing pattern revealed a very restricted spectrotype in two thirds of these IgG. These results which suggested a restricted reactivity between cryo-IgM and IgG fractions were confirmed by the analysis of the interaction between each IgG and each IgM from the cryoprecipitates. All IgM reacted with intact IgG or Fc fragments but another reaction was observed between cryo-IgM and Fab fragments from a limited number of cryo-IgG, with a pattern suggestive of idiotypic specificity. Results of the absorption of each cryo-IgM on Fc or on Fab fragments from the corresponding cryo-IgG also suggested the existence of a reaction between IgM and IgG Fab in addition to that involving IgM Fab and IgG Fc. The coexistence of the 2 reactions should confer a higher stability to the IgM-IgG complex. Therefore, it is possible that the proliferation of one clone of IgM-RF producing B cells would be followed in certain cases by a relatively restricted anti-idiotypic IgG response. The IgM-RF would preferentially react with these anti-idiotypic IgG.