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As a result of a single intraperitoneal treatment with 1 mg/ml of Mannozym (M) the plasma fibronectin (FN) level was significantly increased both in germfree (Gf) and conventional (Cv) mice, and though it started from a lower value in Gf mice, it rose to a similar level to that of Cv animals. The maximum of FN level was observed on the first day after treatment both in Gf and Cv mice. It had returned to normal by the 7th day in Cv mice, but it was higher in Gf mice as compared to untreated controls even on the 14th day. Thus the increase of FN level was of higher degree and longer duration following M treatment in Gf mice than in Cv animals. In treated Gf mice the plasma FN concentration was in the same range as in untreated Cv mice even at the termination of experiment. Both in Gf and Cv mice, there was a relative spleen weight increase, the degree of which was similar, but the duration was longer in Gf mice than in Cv ones.

Binding of purified plasma fibronection to Crithidia luciliae kinetoplast DNA was demonstrated by fluorescence microscopy. The method was suitable for the detection of fibronectin in human plasma diluted 1:256 and 1 microgram/ml concentration of isolated fibronectin. Purified human Clq, monoclonal human myeloma proteins of IgG1 and IgG3 subclasses and calf thymus DNA inhibited the binding of fibronectin to kinetoplasts. The method can be used as a functional assay for fibronectin and for various materials containing fibronectin.

Lower plasma fibronectin (FN) levels were detected in C3H germfree (Gf) mice as compared to conventional (Cv) ones. FN levels increased with aging both in Gf and Cv mice. Stimulation of the immune system with live Newcastle disease virus (NDV) vaccine increased the FN levels in young germfree mice, but had no effect in conventionals.