A study of cells present in lymph draining from a contact allergic reaction in pigs sensitized to DNFB.

Pigs were skin-painted with the contact sensitizing agent 1-fluoro 2,4 dinitrobenzene (DNFB) and lymph cells coming from the site were collected. Half the animals were sensitive to DNFB and half were normal controls. Special attention was paid to cells belonging to the veiled cell series. At 20 hr after DNFB application, some blast cells--on morphological grounds belonging to the veiled cell series--could be observed in the lymph of presensitized animals. But the most predominant finding in these pigs was that, approximately 30 hr after painting, the total cell output began to increase, reaching 10 times the normal level at 70 hr. The increase in the output of lymphoblasts was the most marked, suggesting peripheral sensitization. Such changes were not observed in normal animals. Here the most striking alterations were seen in the veiled cells. Some of these cells were moving ponderously about, apparently in pursuit of other lymph-borne cells, and this activity resulted in the formation of large cellular aggregates. Since it is known that veiled cells are involved in antigen handling, this behaviour probably facilitates the induction of the T-cell immune response. By contrast, the veiled cells from presensitized animals behaved in a more normal manner and the proportion found in aggregates was only briefly increased. In these animals lymphocytes were seen to interact with veiled cells in a manner reminiscent of peripolesis, apparently recognizing antigenic signals on the surface of the veiled cells. It is discussed that this might result in deletion of the antigen-presenting veiled cells, thus controlling the magnitude of the immune response.