Current concept of allergic skin reactions

Synopsis On the basis of literature and experimental work the present views on the mechanism of the development of allergic skin reactions of the contact type are reviewed. Precursors of effector cells originating from stem cells are stimulated by the antigenic complex formed by the application of the hapten to the skin. Autologous skin proteins and macrophages play an important role in this preparatory and antigen recognition phases. Activated T lymphocytes proliferate in the draining lymph node and differentiate into effector and memory cells. The former react to a repeated application of the hapten with release of mediators inducing a skin inflammatory reaction. The latter produce further effector cells thus enhancing the degree of contact sensitivity (booster effect). The hapten application also activates a specific control mechanism consisting of lymphocytes with the same specificity but adverse activity. These cells, called suppressors, restrict the development of further effector cells thus limiting the degree of contact sensitivity. Elimination of suppressor cells leads to an enhancement of the degree of contact sensitivity whereas an intended extreme activation of these cells induces a state of specific immunological unresponsiveness (tolerance).