[Immunity of the skin--infection and percutaneous immunization of rabbits with E. coli ATCC 13676].

After intracutaneous infection of rabbits with a suspension of E. coli which was followed by a transient local inflammation, the local and systemic immune responses were determined using the lymphocyte stimulation test (LTT) and the hemolysis plaque assay (HPA). Lymphocytes of the lymphatic system draining the infected skin area and blood lymphocytes were used. With lymphocytes derived from the local lymph nodes, a substantial increase of specific stimulation in the LTT was detected beginning at day 3 after infection and lasting up to the termination of the experiment (3 weeks). Blood lymphocytes were stimulated at a lower level: The activity showed a peak at day 4 and an elevated level only during a 10-day period. After the intracutaneous infection with E. coli, increasing numbers of antibody-releasing lymph node cells were detected in the HPA. The antibody-secreting cells of the IgM and IgG classes clearly showed an increasing specificity for E. coli lipopolysaccharide coupled to sheep red blood cells. As with the LTT, the highest activities (values of specificity and number of plaque-forming lymphocytes) were observed at the end of the experimental period. An emulsified preparation of a heat-inactivated E. coli culture (E. coli-BKS) which had been applied locally onto the artificially altered skin evoked a similar immunological response after a 2 or 3-weeks treatment. In such animals an increased activity of lymph node cells could be registered by LTT and HPA as compared to reactions from placebo-treated control animals. However, the topical immunization with nonviable E. coli stimulated not only lymphocytes which produced antibodies directed specifically against E. coli lipopolysaccharide as demonstrated by the HPA. An increased number of lymphocytes reacted even with native sheep red blood cells. This observations is discussed in respect of a polyclonal B-cell activation by lipopolysaccharide of the E. coli-BKS.