Direct correlation between delayed footpad reaction and resistance to local bacterial infection.

The resistance to bacteria was studied at the site of delayed footpad reaction in mice immunized with Listeria monocytogenes. When a challenge injection of listeria was given into the footpad of immune mice, no enhancement of bacterial elimination was observed before the generation of delayed footpad reactivity. After the generation of delayed reactivity, an enhanced elimination of listeria or Salmonella typhimurium was observed only at the site of strongly positive delayed footpad reaction elicited with listerial antigen. Such an enhancement in bacterial elimination was also found at the site of delayed footpad reaction induced by immunization with heterologous erythrocytes. Both delayed footpad reaction and local resistance could be transferred locally by immune spleen cells in a dose-dependent fashion, but were completely abrogated when recipient mice were treated with carrageenan or whole-body X irradiation. Macrophage accumulation was an important factor in the expression of resistance at the reaction site. These results suggest that the delayed footpad reaction contributes to host defense by enhancing the local resistance to bacteria.