Cellular basis for differences in humoral immune responses of sheep immunized with living or killed Staphylococcus aureus vaccines.

An immunohistological study was made of immunoglobulin-containing cells and antibody-containing cells in abscesses/granulomas which formed at the injection site, draining popliteal nodes and contralateral popliteal nodes of sheep given either a living Staphylococcus aureus vaccine (Group L), a killed S. aureus vaccine with Freund's complete adjuvant (FCA) (Group K) or FCA alone (Group C). The injections were made subcutaneously in the hind legs and second injections were given 4 weeks later in the same site. Very large numbers of IgM-containing cells were found in granulomas of Groups K and C at 1 week post-injection (PI) but by 2 weeks PI only small numbers were recorded. Following booster immunization, the numbers of IgM-containing cells were greater in abscesses from sheep in Group L than from granulomas from sheep in Group K. Levels for Group C remained low after 1 week PI. There was evidence that the very early IgM-containing cell response in Group K was largely unrelated to specific anti-staphylococcal antibody synthesis. The IgG2-containing cell response was significantly greater than the IgG1-containing cell response in abscesses and nodes in Group L. In contrast, for animals in Groups K and C the IgG1-containing cell response predominated over the IgG2-containing cell response in granulomas and draining nodes. There were generally greater numbers of cells containing anti-staphylococcal antibody in abscesses/granulomas and nodes in Group L than in Group K.