Comparative histology of the mouse bladder following initial infection and re-infection with Escherichia coli.

The present study continues our investigation of the bladder antimicrobial mechanisms following bacterial infection. Since the process of spontaneous clearance of bacteria (E. coli) from the mouse bladder is greatly accelerated upon re-infection, a histopathological comparison was made of initially infected (II) versus re-infected (RI) mice. It was reconfirmed that the spontaneous clearance upon re-infection is indeed much faster than after the initial infection. There were morphological differences between these two courses of infection, as well as in the localization and composition of the inflammatory response. Thus cellular infiltration was more evident in the epithelium of the II mice, whereas the RI animals displayed increased cellular exudation in the lamina propria. It was also found that the dominant cell in the II mouse is the granulocyte and in the RI mouse--lymphocytes, macrophages and plasma cells. This last finding is suggestive of a local immunological process. The overall results are consistent with the notion that a local immune response develops in the infected bladder and participates in the enhanced clearance in RI animals.