Studies were conducted to elucidate the immune cell response at infection sites by performing immunostaining of immune cells with a monoclonal antibody in an experimental Escherichia coli (E. coli) mouse uterine infection model. 1. The incidence of uterine infection by E. coli decreased with the passage of time: 4/4 on Day 1, 4/6 on Day 3, 2/6 on Day 7, and 1/6 on each of Days 14 and 21. It was surmised that clearance of the bacteria from the infection sites was being carried out by immune cells. 2. Beginning from infection Day 1, the infected uterine tissue was observed to undergo a moderate degree of invasion by neutrophils, macrophages, CD4+ T cells, CD8+ T cells and IgA+ B cells. Then, beginning from infection Day 3, there was a mild degree of invasion of the infected uterine tissue by IgM+ B cells and IgG+ B cells. The number of neutrophils in the tissue decreased beginning from infection Day 14, but the degree of invasion of the infected tissue by the other kinds of immune cells remained almost constant through infection Day 21. 3. A comparison was made of the immune responses to local infection by E. coli, and Chlamydia trachomatis (C. trachomatis), an intracellular parasite. It was found that the invasion of the infection site by immune cells occurred earlier in the case of E. coli infection than C. trachomatis infection. In addition, the C. trachomatis infection site was observed to contain greater numbers of macrophages and CD8+ T cells play important roles in the immune defense at sites of infection by C. trachomatis.