Effect of skin painting with oxazolone on the local extravasation of mononuclear cells in sheep.

A characteristic feature of the induction of cell-mediated delayed hypersensitivity reactions by chemicals such as oxazolone is the enlargement of lymphocyte traffic areas in the paracortices of regional lymph nodes. In sheep oxazolone is a powerful immunogen but the cellular changes in lymph efferent from nodes draining areas of oxazolone-painted skin do not differ significantly from responses to conventional antigens. Specific complement-binding antibodies appear in the plasma of sensitized sheep, which respond to secondary challenges with an immediate Arthus reaction. In studies of peripheral lymph from areas of skin painted with oxazolone the number of mononuclear cells in the lymph increased 10--50-fold two days or so after skin painting. Most of these cells were small lymphocytes lacking surface immunoglobulin (presumptive 'T' cells). This big increase in lymphocyte traffic through the skin may be a consequence of the binding to local structural proteins of myriads of oxazolone epitopes. If so, and bearing in mind the large doses of immunogen used in experiments on mice, it is easy to envisage how the traffic areas of lymph nodes expand and become congested with lymphocytes after being flooded with a highly immunogenic and reactive chemical like oxazolone. Whether this is relevant to the induction of cell-mediated immunity is unknown.