The secondary immune response to Staphylococcus aureus vaccines in efferent popliteal lymph of sheep

The secondary immune response to live and killed Staphylococcus aureus vaccines was studied in efferent popliteal lymph of sheep. Animals were immunized with either live or killed S. aureus intracutaneously on the lateral hock, in an area draining into the popliteal lymph node. Six weeks later, an efferent popliteal lymphatic vessel in the vaccinated leg was cannulated, and 48 hr after surgery a second inoculation (identical to the primary) was placed in the skin adjacent to the primary vaccination lesion. A dramatic decrease in lymphocyte output ('cell shutdown') was observed in lymph collected from sheep given the secondary inoculation of live S. aureus during the first 8 hr after inoculation. However, only a moderate decrease in lymphocyte output occurred in lymph from animals receiving killed S. aureus or from control animals. The proportion of eosinophils in lymph collected from animals given live S. aureus increased to a peak (14% of total leucocytes in lymph) between 6 hr and 8 hr, and returned to prechallenge levels by 24 hr post-inoculation. The percentage of neutrophils in lymph peaked between 8 hr and 1 day after injection of live bacteria. This granulocyte response was not observed in animals given killed S. aureus or control animals. IgM-, IgG1- and IgG2- containing cells (-cc) in lymph were quantified by indirect immunofluorescence. Animals given live S. aureus produced lymph with greater numbers of Ig-cc of these isotypes than those given killed organisms. The ratio of IgG2-cc:IgG1-cc was significantly greater in lymph from animals given live S. aureus from Day 2 to Day 6 post-challenge. IgM and IgG1 anti-staphylococcal antibody levels increased in lymph collected from all vaccinated animals, but only sheep given live S. aureus showed any increase in levels of IgG2 antibody.