Experimental allergic gingivitis: II. Development of chronic gingivitis or local non‐reactivity after multiple challenges in the rat

Immunized and non‐immunized rats were given 6 or 8 intragingival injections of bovine serum albumin or saline at intervals of 7, 3, 2 or 1 days. Biopsies of the gingiva were ob tained one day after the last challenge. The severity of inflammation in the oral mucosa decreased with increasing intervals between injections. Gingivitis did not develop in con trol rats, the mucosa of which was punctured 8 times without injection of solution. It is suggeseed that intragingival challenges give rise to the appearance of inhibitory factors, which are operative only when injections are administered at long spaced intervals.