Study on local immune response in Escherichia coli-induced experimental urinary tract infection in mice--infiltration of Ia-positive cells, macrophages, neutrophils, T cells and B cells

We studied the local immune response in a mouse experiment with acute ascending cystitis and pyelonephritis. The experimental infections were induced in BALB/c female mice by transurethral instillation of Escherichia coli O6. Immune response cells were stained, including Ia-positive cells, macrophages, neutrophils, T cells (CD4+ and CD8+) and B cells (IgA, IgM, IgG-positive B cell). They were stained by the immunohistochemical method (ABC method) using monoclonal antibodies against lineage specific antigens except for neutrophils that were readily identified by the standard hematoxylin-eosin. Even in the control mice having no evidence of the infection, mucosa associated lymphoid tissue (MALT) consisted of macrophages, Ia-positive cells and T cells that were sparingly found in the urinary tract tissue and renal parenchyma. Ia-positive cells, macrophages, neutrophils, T cells (CD4+, CD8+) and IgA positive B cells were significantly infiltrated in the bladder submucosa from 6 hours after bacterial inoculation. The infiltration of similar immune response cells was found in the submucosa of the renal pelvis, except for IgA positive B cells that appeared one day after the induction of the infection. In renal parenchyma, Ia-positive cells appeared at 6 hours after introduction of the infection, followed by an infiltration of neutrophils, macrophages and T cells (CD4+, CD8+) at the first day, and IgA positive B cells at the third day. These results are summarized as follows. When microbes invaded the urinary tract tissue, a significant number of Ia-positive cells infiltrated, which were initially present in normal urinary tract tissue. Subsequently, neutrophils, macrophages and T cells (CD4+, CD8+) appeared in the lesion followed by a delayed occurrence of IgA positive B cells.