Resorption of insoluble, heterologous, fluorescein-collagen sponges in sensitized and non-sensitized rats.

Sponges of insoluble bovine collagen were slowly resorbed over a 35-day period when implanted under the back skin of rats. The cellular picture was typical of a mild foreign-body reaction. The reaction to fluorescein-labelled collagen sponges was similar but there was evidence also of a weak immunological response. An acute inflammatory reaction with massive oedema was elicited when fluorescein-labelled collagen sponges were implanted in rats previously sensitized to either fluorescein-collagen or fluorescein-bovine serum albumin. The early invasion by PMN leucocytes subsided after 4 days and caused no observable breakdown of the sponge. The implanted material was rapidly encapsulated by fibrous tissue which was then resorbed along with the sponge between the 7th and 12th day. Macrophages were very active in the sponge at this time, sometimes forming giant cells. Fibroblasts were invading from the periphery with the development of the granulation tissue. The small residue which remained after this time was overrun by granulation tissue and was slowly resorbed up to the 35th day. Throughout the period of study there was only a weak local immunological response after the 28th day. The level of circulating antibodies against the fluorescein hapten was high, but the titre for the antibodies against bovine collagen remained low. The significance of these findings in the pathological destruction of connective tissue is discussed.