Functional characteristics of veiled cells from canine prenodal lymph.

The surgical interruption of afferent lymphatics in the hind limb of dog leads to peripheral lymph stasis. The stagnated lymph contains large numbers of immunocompetent cells originating solely from the skin. This experimental model allows a study of the functions of the afferent skin-draining lymph cell population, the recovery and assessment of the lymphokines and other mediators liberated by these cells during the culture, and the production of anti-sera against different types of lymph cells. In the present study, we focused on the functional, morphological and cytochemical evaluation of the non-lymphoid cells, isolated from the whole lymph cell population by means of the gradient centrifugation technique. The non-lymphoid cells were large, with an irregularly-shaped nucleus and numerous cytoplasmic projections, giving them a "veiled" cell (VC) appearance. All VC were strongly positive for DLA-class II antigens and membrane-associated ATP-ase, and 60% of them exhibited the activity of non-specific esterase. In the functional assays, VC displayed the potent accessory-cell activity in the mitogen-induced response of autologous blood- and lymph-derived lymphocytes. In the mixed leukocyte cultures, VC acted as stimulators of the allogeneic and autologous lymphocyte proliferation. The high spontaneous and mitogen-induced responsiveness of the whole lymph cell population was found to be dependent on the presence of VC. The small number of VC (5% of cultured cells) was sufficient to produce the above-mentioned effects. These results indicate that VC is a cell responsible for the antigen presentation in the skin-associated immune reactions in dog, which is relevant to the observations on similar cells from the other species.