Effects of cryoglobulins and aggregated IGG on in vitro monocyte phagocytosis.

Monocyte yeast cell phagocytosis (YCP) was low in presence of cryoglobulins(CG) from 7 of 7 patients with SLE and RA with vasculitis and from 2 of 5 patients with essential cryoglobulinaemia. IgM and C3 were detected only in CG associated with low YCP. Furthermore, low YCP was only found with CG isolated from hypocomplementaemic sera. The results also showed low YCP when heat-aggregated IgG (HAG) greater than or equal to 19S was added to the culture medium. In the presence of HAG or SLE-sera, preopsonized yeast cells could be adequately phagocytosed by monocytes whereas, in parallel cultures, the phagocytosis of untreated yeast cells was low. It is possible that CG and HAG impair YCP in the same way as SLE-sera. The nature of this presumed common mechanism has not been clarified in this limited study. The findings are, however, compatible with the possibility that immune complexes may interfere with the opsonization of the yeast cells, possibly through inactivation of complement components.