Soluble FcγR (sFcγR): Detection in Biological Fluids and Production of a Murine Recombinant sFcγR Biologically Active in vitro and in vivo

Soluble forms of receptors for the Fc portion of IgG (sFcγR) were detected in biological fluids from mice and humans. In mouse bearing tumors, circulating amounts of sFcγR increased concurrently with tumor growth. Tumors secreting IgG2a, IgG2b or IgG3 led to a 5- to 10-fold increase in serum sFcγR levels whereas tumors secreting IgG1, IgGA or other types of tumors (non Ig B cell tumors, T cell lymphoma and a melanoma) increased 2- to 3-fold the levels of circulating sFcγR. In the human, sFc7#x03B3;R were also detected in whole unstimulated saliva. Levels of sFcγRII and of sFcγRIII were variable and did not seem to depend on the dental status of the individuals. Finally, a murine recombinant sFcγR (rsFcγR) composed of the two extracellular domains of Fcγ RII was produced by culture of transfected L cells in bioreactors. The purified rsFcγR was found to inhibit antibody production in vitro in anti-SRBC responses and by cultures of small B cells stimulated by anti-IgM antibodies in the presence of IL-4 and IL-5. Moreover, the i.p. injection of this material into adult mice immunized with SRBC led to a decrease of IgG antibody production by splenocytes, as measured by a hemolytic plaque assay, and in serum, as measured by antigen-specific ELISA.