Histopathological studies of reactions in mice injected with aluminum-adsorbed tetanus toxoid.

Histopathological observations of changes at the injection site in mice were made for 20 weeks after a single intramuscular (im) injection of aluminum hydroxide-adsorbed tetanus toxoid (Alum-TT), plain tetanus toxoid (TT), or aluminum adjuvant (Alum alone). Marked injury to muscle fibers and infiltration of neutrophils around the aluminum remnants were observed, and some microabscesses were occasionally formed, after im injection of Alum-TT. Some mature alum-granulomas were seen in the Alum-TT group, while the Alum alone group had only a few immature alum-granulomas. The TT group showed only slight injury to muscle fibers and acute inflammation at an early stage. In the Alum-TT group, well-developed lymphold tissues and granulomatous lesions were still observable even 20 weeks after the injection; however, these changes had already diminished in the Alum alone group by that time. These findings could serve as good models for undesirable local reactions to aluminum-adjuvanted vaccines.