Degranulation of Basophilic Leukocytes in Allergic Contact Dermatitis Reactions in Man

Abstract

Basophilic leukocytes participating in allergic contact dermatitis in man underwent progressive degranulation over the course of several days after skin test. Less than 10% of basophils were degranulated in 24-hr reactions, but more than 60% were degranulated by 72 hr. In the electron microscope individual basophil granules developed looser packing of their constituent particles, focal replacement of particles by finely granular material, and eventual loss of all visible granule contents, changes that were progressive between 2- and 3-day reactions. However, granules undergoing these changes retained their limiting membranes as well as their identity in the cytoplasm. Empty granules appeared as membrane-bound vacuoles having the size and shape of intact basophil granules. In contrast to the findings in a case of basophilic leukemia, communication of granules with each other was extremely rare and communication of granules with the plasma membrane was not observed. However, membranebound vesicles, the size of pinocytotic vesicles and larger, were abundant in these basophils. Many vesicles were observed free in the cytoplasm, but others were in communication with the cytoplasmic granules or with the plasma membrane. Vesicles often contained finely granular material of the type occurring in altered granules and rarely contained material morphologically similar to the particles of intact granules. These vesicles may provide a transport mechanism for piecemeal release of basophil granule contents, in addition or as an alternative to the commonly accepted exocytotic pathway of basophil degranulation.